Class 8

Haryana State Board HBSE 8th Class Science Solutions Chapter 14 Chemical Effects of Electric Current Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 14 Chemical Effects of Electric Current

HBSE 8th Class Science Chemical Effects of Electric Current Textbook Questions and Answers

Question 1.
Fill in the blanks:
(а) Most liquids that conduct electricity are solutions of __________ and __________.
(b) The passage of an electric current through a solution causes __________ effect.
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the __________ terminal of the battery.
(d) The process of depositing a layer of any desired metal on another metafile object, by means of electricity, is called __________.
Answer:
(a) acids and bases
(b) chemical
(c) negative
(d) electroplating

Question 2.
When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection, dan yon explain the
Answer:
Yes, the solution is a good conductor of electricity. The reason is that tote solution is a good conductor of electricity, so the needle get deflected.

Question 3.
Name three liquids, which when tested in the manner shown in figure, may cause the magnetic needle to direct.
Answer:
Tap water, lime water, vinegar.

Question 4.
The bulb does not glow in the setup shewn in figure. List the possible reasons. Explain your answer.
Answer:
If the bulb does not glow it may be because of some reasons like the bulb may be fused. Replaced with a new bulb, if it still does not glow, it shows that the connection of wires may be loose. After tightening connetions if still the bulb does not glow, then it is for sure that the solution does not conduct electric current.

Question 5.
A tester is used to check the conduction of electricity through two liquids, labeled A and B. It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. You would conclude that
(i) liquid A is a better conductor than liquid B.
(ii) liquid Bis a better conductor than liquid
(iii) both liquids are equally conducting.
(iv) conducting properties of liquid cannot be compared in this manner.
Answer:
(ii) liquid A is a better conductor than liquid B.

Question 6.
Does pure water conduct electricity? If not, what can we do to make it conducting?
Answer:
Some salt can be added to it to make it a conductor.

Question 7.
In case of fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.
Answer:
Water is a good conductor of electric current. So, the firemen shut off the electric supply before spraying water to save themselves and other people from electrocution.

Question 8.
A child staying in the coastal region tests the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?
Answer:
Drinking water has been processed and purified before supplying it to the houses. Many salts and minerals have been removed from it, so it has decreased its conductivity. On the other hand the sea water is rich in salts, and other acids and basic substances, that is why it is a better conductor of electricity and deflects the needle more than the purified drinking water.

Question 9.
Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.
Answer:
No, it is highly dangerous to carry on electric repairs in water, as water is a good conductor of electricity. It can cause electrocution.

Question 10.
Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise she found that the compass needle showed deflection. What could be the reasons?
Answer:
While it rains, the raindrops get mixed with the suspended particles of the air. So, they do not remain pure. It becomes the mixture of salts and other impurities thus shows conduction of electricity.

Question 11.
Prepare a list of objects around you that are electroplated.
Answer:
Following objects around us are electroplated, rims of cycles, door handles, taps, showers, metallic pens, artificial jewellery, utensils, metallic almirahs, buckles of clothes and belts etc.

Question 12.
The process that you saw in Activity 14.7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transfered to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?
Answer:
The impure copper rod should be attached to the positive terminal because the free copper will get drawn towards the negative terminal to be get deposted, so the copper from impure rod will get collected in the pure copper plate.

Extended Learning – Activities and Projects

Question 1.
Test the conduction of electricity through various fruits and vegetables. Display your result in a tabular form.
Answer:
For self attempt.

Question 2.
Repeat the Activity 14.7 with a zinc plate in place of the copper plate connected to the negative terminal of the battery. Now replace zinc plate with some other metallic object and again repeat the activity. Which metal gets deposited over which other metal? Discuss your findings with your friends.
Answer:
For self attempt.

Question 3.
Find out if there is a commercial electroplating unit in your town. What objects are electroplated there and for what purpose? (The process of electroplating in a commercial unit is much more complex than what we did in Activity 14.7). Find out how they dispose off the chemicals they discard.
Answer:
For self attempt.

Question 4.
Imagine that you are an ‘entrepreneur’ and have been provided a loan by a bank to set up a small electroplating unit. What object you would like to electroplate and for what purpose? (Look up the meaning of‘entrepreneur’ in a dictionary).
Answer:
For self attempt.

Question 5.
Find out the health concerns associated with chromium electroplating. How are people trying to resolve them?
Answer:
For self attempt.

Question 6.
You can make a fun pen for yourself. Take a conducting metal plate and spread a moist paste of Potassium Iodide and starch. Connect the plate to a battery as shown in Fig. 14.11. Now using the free end of the wire, write a few letters on the paste. What do you see?

For more information on this topic visit:
www.tutorvista.com/content/physies/phys- ics-iv/thermalchemical-currents/chemical-ef- fects-current.php
www.physchem.co.za/Redox/ Electrolysis.htm
electronics .howstuffworks.com/3 ed ,htm
Answer:
For self attempt.

HBSE 7th Class Science Chemical Effects of Electric Current Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is electric current?
Answer:
Flow of electrons is called current.

Question 2.
How can we check current?
Answer:
By using a tester.

Question 3.
What are conductors?
Answer:
Substances which allow the electric current to pass through them are called conductors.

Question 4.
What are insulators?
Answer:
Substances which do not allow electric current to pass through them are called insulators.

Question 5.
Name any conductor.
Answer:
Copper.

Question 6.
Name any insulator.
Answer:
Plsatic.

Question 7.
Are liquids conductor of electricity?
Answer:
Yes, some liquids are conductors of electricity.

Question 8.
Name any liquid conductor.
Answer:
Tap water.

Question 9.
Can distilled water conduct electricity?
Answer:
No.

Question 10.
How can distilled water be made conductor of electricity?
Answer:
By adding some salt to it.

Question 11.
How can we check magnetic effects of electric current?
Answer:
By using magnetic compass.

Question 12.
How does magnetic compass show magnetic effect?
Answer:
By deflection.

Question 13.
What makes most of the liquids good conductors of electricity?
Answer:
Acids, bases and salts.

Question 14.
Name any two liquids except water which conduct electricity.
Answer:
Vinegar and lemon juice.

Question 15.
What is an electric circuit?
Answer:
Path of the flow of electric current is called electric circuit.

Question 16.
What in a electric circuit shows that current is passing through it?
Answer:
Glowing bulb.

Question 17.
Will a bulb glow when circuit is completed in an insulating solution?
Answer:
No.

Question 18.
Which effect of electric current causes the bulb, to glow?
Answer:
Heating effect.

Question 19.
What glows in a bulb?
Answer:
Filament

Question 20.
What is LED?
Answer:
LED is like a bulb which even glows at low or a small current.

Question 21.
What is full form of LED?
Answer:
Light Emitting Diode.

Question 22.
What are the better sources of light than bulbs and tubes?
Answer:
C.F.L.

Question 23.
What is used in CFLs?
Answer:
Mercury.

Question 24.
What other object can be used in place of bulbs to see the flow of electric current?
Answer:
Magnetic Compass.

Question 25.
What are the metal rods dipped in liquids to which cells are attached called?
Answer:
Electrodes.

Question 26.
What are the bubbles seen near electrodes after passing current through a conducting solution?
Answer:
Hydrogen and Oxygen gas.

Question 27.
When we pass current through a conducting solution of water, which gas bubbles will appear near positively charged electrode?
Answer:
Oxygen.

Question 28.
Which gas will accumulate near negative electrode when electric current is passed through a conducting solution of water?
Answer:
Hydrogen.

Question 29.
Name any chemical effect of electric current.
Answer:
Electroplating.

Question 30.
What is electroplating?
Answer:
Coating of a desired metal oft other metallic surface using electric current is Called electroplating.

Question 31.
To which terminal of the battery the metal meant for electroplating is attached?
Answer:
Negative terminal.

Question 32.
Which metal is plated on handlebars of cycles and rims of wheels?
Answer:
Chromium.

Question 33.
Which metal is plated on the iron to protect it from mist and corrosion, which is used in building bridges? .
Answer:
line.

Question 34.
Is air an insulator or conductor?
Answer:
Insulator.

Question 35.
In which direction does current flow?
Answer:
Current flows from negative terminal to the positive terminal.

Short Answer Type Questions

Question 1.
What is an electric Current?
Answer:
Plow of electrons is called electric current. Negatively charged electrons flow from negative terminal to the positive terminal and this is called electric current and the path through which it flows is called electric circuit.

Question 2.
What is a tester?
Answer:
Tester is an instrument which is Used to check the flow of electric current. It is attached to the terminal of the electric circuit, if the bulb attached to tester glows, it confirms the passage of current.

Question 3.
What are conductors?
Answer:
Substances which allow the electric current to pass through them are called conductors. Substances through which electric current passes easily are called good conductors and substances through which current passes partially or in small quantity they are called bad conductors. Substances like copper, iron, aluminium etc. are called conductors.

Question 4.
What are insulators?
Answer:
Substances which do not allow the electric current to pass through them are called insulators. Electric current do not pass through them and do not show any effect of electric current. Substances like wood, plastic, rubber* distilled water etc. are insulators.

Question 5.
Can electric current pass through liquids? Explain.
Or
Are liquids Conductor or insulator? Explain.
Answer:
Some liquids allow the electric current to pass through them and some liquids do not allow the electric current to pass through them. Mostly liquid conductors are solutions of acids, bases and salts. Liquids free from acids, bases and salts are insulators e.g. mineral water is pure form of water it is an insulator. Lemon juice vinegar are conductors.

Question 6.
You are given a solution containing lemon juice and salt.
You are told to check whether it is a conductor or insulator. How will you show it diagrammatically.
Answer:

Question 7.
You are given distilled water. Check if it is a conductor or insulator?
Answer:
Distilled water is taken in a Plastic container. The free ends of the tester are dipped in the container. After waiting for a few miniutes we will find that the bulb does not glow. It confirms that distilled water does not allow electric current to pass through it so it is an insulator.

Question 8.
What is magnetic effect of current?
Answer:
When current is passed through a coil it behaves like a strong permanent magnet. The strength of the magnet depends upon the current through the wire and number of turns of the coil. This coil will continue to behave like a magnet still the current passes through it.

Question 9.
Draw an electric circuit showing different components like a battery, conducting wire, bulb and free ends dipped in conducting solution.
Answer:

Question 10.
What is LED, why is it a most preferable source of light?
Answer:
LED means Light Emitting Diode. Ordinary bulbs do not glow when current is small. They need large supply of current to emit light. So, they consume more current, they thus prove to be costly. On the other hand LED can glow even at very small supply of electricity and consume small current. Thus it is economical.

Question 11.
Why does a bulb glow when electric current passes through it?
Answer:
When electric current passes through a bulb, the filament of the bulb starts heating up. This is called heating effect of current. The filament gets heated up to such a high temperature that it starts glowing.

Question 12.
How can we prove conduction of substances when current is very small and the bulb does not glow?
Answer:
When current passing through a conductor is very small, the bulb does not glow. In such case we use magnetic compass to know the conduction of current. Electric current has magnetic effect which deflects the magnetic compass proving that current is flowing around the compass.

Question 13.
Why do we need magnetic compass to test the conduction of electric current?
Answer:
Sometimes when we make to flow current through a conductor, the bulb does not glow. This is because the electric current flowing through conductor is so small, that the filament of the bulb does not get heated up to the temperature where it starts glowing. So, in case of small current we need magnetic compass to test the conduction. juice is mixed in distilled water it becomes conductor of electricity.

Long Answer Type Questions

Question 1.
What happens when we add a pinch of salt or some lemon juice in distilled water to test its conduction of electric current?
Answer:
Distilled water does not allow the electric current to pass through it. But when we add some salt or the lemon juice to it, it starts conducting electric current and shows deflection of magnetic compass because salts and acids are conductors of electric current when salt or lemon juice is mixed in distilled water it becomes conductor of electricity.

Question 2.
Why is it not advisable to touch any electrical appliance with wet hands?
Answer:
It is not advisable to touch electrical appliances with wet hands because it can send electric shock in our body. Water is conductor of electric current. It easily allows electric current to pass through it, so when we will touch the switch or electrical appliance with wet hands the water will alow the current to pass through it and electric current will reach our body giving us shocks. This can sometimes prove very dangerous even fatal.

Question 3.
What is Electroplating? How does it take place?
Answer:
Electroplating is the process of coating a desired metal on an undesired metal surface using electric current.

Metallic plate and the substance requiring coating are dipped in conducting solution with conducting wires. The object to be coated is attached to the negative terminal. When electric current is passed through the solution, the compounds of the conducting solution start breaking and free metallic particles get deposited on the object at negative terminal of battery. In this way we can get a coating of desired metal on any object by preparing suitable conducting solution and using suitable electrodes.

Question 4.
What are the advantages of electroplating?
Answer:
Electroplating has many advantages.

• It is used to coat metal surfaces with desired metal coatings.
• It saves metal surfaces from rusting
• It saves corrosion of surfaces of metals.
• Coating of chromium on metals give lustre to objects.
• Cheap metals like iron, aluminium etc. can be coated with costly metals like silver, gold etc. to give them rich look as in case of artificial jewellery.
• It can make reactive metals like iron etc. less reactive and they can be used for storing food items etc.

Question 5.
Show experimentally that a current carrying wire behaves like a magnet.
Answer:
As in figure shown below, a wire is fixed along the edge of a table. Place a magnetic compass near the wire. Connect the two ends of the wire to a battery cell. There is a deflection in the magnetic compass. Place the compass at different points on the table at varying distances from the wire. Observe the deflection in each case. We guess from this activity that a current carrying wire behaves like a magnet. When the current is stopped, the associated megnatic property also vanishes.

Question 6.
How can you prepare an electric pen?
Answer:
Take a filter paper and soak it into potassiumiodide and starch solution. Spread it on a metal sheet. Now join two connecting wires to the terminals of battery. Attach the wire

connected at positive end to plate. Now write on the sheet the wire attached to negative terminal. Wherever you will write blue coloured inck will appear. This happen due to electrolysis of potassium iodide solution which produces iodine. Iodine on reaction with starch produce ink of blue colour.

Chemical Effects of Electric Current Class 8 HBSE Notes

• Flow of electrons is called current.
• Those objects which allow the current to pass though them are called conductors.
• Those objects which do not allow the current to pass through them are called insulators.
• Objects like copper, aluminium etc. and almost all metals are good conductors of electricity.
• Objects like wood, plastic, rubber etc. do not allow electricity to pass through totem and are – thus bad conductors of electricity and are thus called insulators.
• liquids like’vinegar, lemon juice, tap water etc. are conductors of electricity and distilled water is an insulator. Salted distilled water becomes a conductor.
• Electric current has many chemical effects.
• Electric current when passed through a conducting solution causes different changes in it, these are called chemical changes.
• It may evolve gas after breaking the chemical solution into different elements. Chemical effects depend upon the conducting solution and the electrodes used.
• Electrodes are the rods of different metals immersed in conducting solution to complete the circuit and cause the flow of electrons.
• Electric current when passed through a conducting solution can cause electroplating.
• Electroplating is the process of depositing a layer of any suitable metal on another metal.

Haryana State Board HBSE 8th Class Science Solutions Chapter 15 Some Natural Phenomena Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 15 Some Natural Phenomena

HBSE 8th Class Science Some Natural Phenomena Textbook Questions and Answers

Question 1.
Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth.
Answer:
(b) A copper rod

Question 2.
When a glass rod is rubbed with a piece of silk cloth the rod
(a) and the cloth both acquire positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire negative charge.
(d) becomes negatively charged while the cloth has a positive charge.
Answer:
(b) becomes positively charged while the cloth has a negative charge.

Question 3.
Write T against true and F against false in the following statements:
(а) Like charges attract each other. (T/F)
(b) A charged glass rod attract a charged plastic straw. (T/F)
(c) Lightning conductor cannot protect a building from lightning. (T/F)
(d) Earthquakes can be predicted in advance. (T/F)
Answer:
(a) False
(b) True
(c) False
(d) False

Question 4.
Sometime, a crackling sound is heard while taking off sweater during winters. Explain.
Answer:
This occurs due to electric discharge between sweater and body. Some energy is always released with electric discharge, which in this case is released in form of a cracking sound.

Question 5.
Explain why a charged body loses its charge if we touch it with our hand.
Answer:
When we touch a charged body, it loses its charge, due to process of earthing. Our body is good conductor of electricity and transfers the charges to the earth.

Question 6.
Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
Answer:
Destructive energy of an earthquake is measured in Ricther Scale. Yes, it will be recorded in this scale. Earthquake with megnitude of 3 on Richter Scale is not much destructive.

Question 7.
Suggest three measures to protect ourselves from lightning.
Answer:
Three measure to stay protected from lightning are:

• Stay indore or under covered area.
• Don’t take bath during lightning.
• We should not use T.V. or phone during lighning.

Question 8.
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?
Answer:
A charged balloon is atracted by another charged balloon because both carry same charge like charge always repel each other. While the uncharged balloon is attracted by charged balloon due to unlike charged.

Question 9.
Describe with the help of a diagram an instrument which can be used to detect a charged body.
Answer:
An electroscope can be used to detect if a body is charged or not. When the metal strips repel each other proves that the body is charged as repulsion is the sure test to detect if a body carries charge or not.

Question 10.
List three states in India where earthquakes are more likely to strike.
Answer:
Kashmir, Punjab and Gujarat are more prone to earthquake.

Question 11.
Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?
Answer:
We will take following precautions :

• We will try to move to an open space.
• If we are driving, we will slow down the vehicle and move slowly away from that area.
• We will not take shelter under trees or buildings.

Question 12.
The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.
Answer:
No, we will not take an umbrella, as this will increase the risk of lighting because wide objects are more prone to lightning strike.

Extended Learning – Activities and Projects

Question 1.
Open a water tap. Adjust the flow so that it forms a thin stream. Charge a refill. Bring it near the water stream. Observe what happens. Write a short report on the activity.
Answer:
For self attempt.

Question 2.
Make your own charge detector. Take a paper strip roughly 10 cm x 3 cm. Give it a shape as shown in Fig. 15.15. Balance it On a needle. Bring a charged body near it. Observe what happens. Write a brief report, explaining its working.
Answer:
For self attempt.

Question 3.
This activity should be performed at night. Go to a room where there is a fluorescent tube light. Charge a balloon. Switch off the tube light so that the room is completely dark. Bring the charged balloon near the tubelight. You should see a faint glow. Move the balloon along the length of the tube and observe how glow changes.
Caution: Do not touch the metal parts of the tube or the wires connecting the tube with the mains.
Answer:
For self Attempt.

Question 4.
Find out if there is an organisation in your area which provides relief to those suffering from natural disaster. Enquire about the type of help they render to the victims of earthquakes. Prepare a brief report on the problems of the earthquake victims.
For more information on these topics, visit:
→ science.howstuffworks.com/lightning.htm
→ science.howstuffworks.com/ earthquake .htm
→ www enchantedlearning.com/subjects/ astronomy/planets/ earth/continents.shtml
Answer:
For self attempt.

HBSE 7th Class Science Some Natural Phenomena Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Name any three natural phenomena.
Answer:
Earthquakes, cyclones, lightning.

Question 2.
According to ancient Greeks who invented thunderbolts?
Answer:
Goddess of Wisdom Minerva.

Question 3.
What are the sparks seen in sky during thunderstorms?
Answer:
Lightning.

Question 4.
Which resin did Greeks knew, produced sparks on rubbing continuously?
Answer:
Amber.

Question 5.
What happens when we rub a plastic scale with our hair?
Answer:
It gets charged.

Question 6.
What happens when charged plastic scale is brought close to bits of paper?
Answer:
Papers get attracted towared scale.

Question 7.
What happens when we rub an inflated balloon and let it free near a wall?
Answer:
Balloon gets attached to the wall.

Question 8.
How many types of charges are gained by rubbing objects?
Answer:
Two.

Question 9.
Name the charges bodies acquire on rubbing.
Answer:
Positive charge and negative charge.

Question 10.
What happens when similar charged bodies are brought close?
Answer:
They repel each other.

Question 11.
What happens when two different charged bodies are brought close?
Answer:
They attract each other.

Question 12.
What will happen when a charged glass rod is brought close to a charged straw?
Answer:
They will attract each other.

Question 13.
What will happen when a charged pen refil is brought close to a charged balloon?
Answer:
They attract each other.

Question 14.
Which charge is conventionally called a positive charge?
Answer:
Charge on a charged glass rod.

Question 15.
A charged glass rod attracts a charged straw. What is the charge on the charged straw?
Answer:
Negative charge.

Question 16.
What is the electric charge generated by rubbing called?
Answer:
Static electricity.

Question 17.
What is the static electricity?
Answer:
Charges which are produced by rubbing and are not movable are called static electricity.

Question 18.
How is electric charges different from static charges?
Answer:
Electric charges can flow but static charges cannot move.

Question 19.
What is used to transfer electrical charges from one body to another?
Answer:
Metallic conductors.

Question 20.
What is the transfer of charges from one body to earth is called?
Answer:
Earthing.

Question 21.
What provision is made in buildings to prevent electrocution?
Answer:
Earthing of wires is done.

Question 22.
How a huge energy is produced during thunderstorm?
Answer:
By repulsion of negative charges from clouds and positive charges from ground.

Question 23.
What is the process of meeting of negative charges from clouds with positive charges from ground to release huge energy called?
Answer:
Electric discharge.

Question 24.
Which place is safe during thunderstorms and lightning?
Answer:
Covered vehicles and buildings.

Question 25.
What should be considered as alert signs to get a safe place during thunderstroms?
Answer:
Hearing thunder without lightning.

Question 26.
Is sitting on a motor-cycle safe during lightning?
Answer:
No.

Question 27.
Where should one take shelter in open during lightning?
Answer:
Under small trees.

Question 28.
Is it safe to use wired phones during lightning?
Answer:
No.

Question 29.
Can a lightning victim electrocute another person?
Answer:
No.

Question 30.
What harms can lightning cause in a lightning victim?
Answer:
Loss of memory, loss of hearing or sight, broken bones etc.

Question 31.
What is the device used to save multistoryed buildings from lightning.
Answer:
Lightning rod.

Question 32.
Where is the lightning rod attached to protect the building from lightning?
Answer:
On the top of the building.

Question 33.
One end of the lightning rod is left loose in the air, where is the other end fixed or attached?
Answer:
Other end of the rod is attached to the ground.

Question 34.
Which fish can give electrical shock?
Answer:
Electrical eel.

Question 35.
What is the capacity of producing electric current in an electrical eel?
Answer:
650 volts.

Short Answer Type Questions

Question 1.
How can charging take place by rubbing?
Answer:
When a plastic comb is rubbed with hair it starts attracting small pieces of paper. Similarly, when two straws are rubbed with polythene and are brought close they repel each Other. Rubbing charges the comb and straws by loading charges on comb and straws, The polythene and hair against which straws and combs are charged also get charged.

Question 2.
How many types of charges do things acquire on rubbing?
Answer:
Charges acquired by objects are of two types named positive charge and negative charge. Charge acquired by a glass rubbed with silk is called positive charge and the charge acquired by the silk is called the negative charge.

Question 3.
How are negative and positive charges related to each other?
Answer:
Positive charges repel each other and negative charges repel each other. In other words similar charges repel each other. On the other hand negative charge is attracted by positive charges or in simple words opposite charges attract each other.

Question 4.
What is static electricity? How is it different from electric current?
Answer:
The electrical charges acquired by bodies on rubbing are called static electricity. These charges are called static because, they cannot move. This is the difference static electricity and electrical current has. Electrical current can move or flow but static electricity cannot move or flow.

Question 5.
What is electrical discharge?
Answer:
Transfer of charges from a body is called electrical discharge. If we touch a charged object, the charge gets transferred to the earth through our body. We say that the object is discharged. This is also called earthing. Electrical discharge can take place between any two conducting bodies.

Question 6.
How electrical discharge takes place in clouds?
Answer:
During thunderstorms the negative charges get accumulated near the clouds and positive charges accumulate near ground. When these negative and positive charges meet, electrical discharge takes place between clouds and grounds. It produces huge amount of energy which is released as lightning and thunder.

Question 7.
How do clouds get charged during thunderstorms?
Answer:
During thunderstorm there is a vigorous movement of air current in upward and downward direction i.e. in opposite direction. This is similar to rubbing of objects, this vigorous movements of water droplets in clouds cause charging of the clouds.

Question 8.
How does lightning strike during thunderstroms?
Answer:
During thunderstorms, the opposite charged clouds and ground come in contact and electrical discharged takes place between clouds and ground and huge energy is released as lightning. This is called lightning strike. Electrical discharge can take place between clouds and ground, clouds and human body, clouds and building etc.

Question 9.
How can we protect ourselves from lightning during thunderstorm when we are out of our home?
Answer:
Following precautions should be used when we are out during thunderstorm:

• We should not stay in open vehicles or places.
• Should not carry unbrella.
• Should not take shelter under tall trees or under poles etc.
• If shelter has to be taken, then it should be taken under smaller trees.

Question 10.
What precautions should we take to secure ourselves from lightning stroke during thunderstorm when we are in our homes?
Answer:
Following precautions should be taken while in house :

• We should not use wired phone.
• Electrical appliances should be plugged off.
• Should not bathe in running water.

Question 11.
Why is it advised to take shelter under smaller trees while in open during thunderstorms?
Answer:
During thunderstorms, we should take shelter under smaller trees because electrical discharge can easily take place with tall trees, so they are easy targets of lightning. While smaller trees are not in reach of lightning often.

Question 12.
How does a lightning rod protect a building from lightning?
Answer:
Lightning rods are installed on the top of the buildings. One end of the rod is left in open and the other one is connected to the earth.When lightning strikes the building, the charges are directly transferred to earth by the rod, this is called earthing. Earthing thus saves the buildings from lightning strike.

Question 13.
Why the Electric Eel is so called?
Answer:
Eel found in South America emits electric discharge from its body. It can produce electric current of 650 volts. It emits discharge to attack its enemies, to give shock to the prey. It can also give shock to human beings too. As these Eels produce electric discharge, they are called electric Eels.

Question 14.
What is an earthquake? How is it measured?
Answer:
Sudden trembling and shaking of the earth is called an earthquake. Due to sudden movements in the uppermost layer of the earth, the earth starts trembling, this movement of earth is called an earthquake. The magnitude of the earthquake is measured through an instrument called seismograph and it is measured on Richter scale.

Long Answer Type Questions

Question 1.
What is static electricity? How many kinds of charges are there?
Answer:
The electrical charge produced due to rubbing of objects is called static electricity. This charge cannot move as the electric current moves. These types of charges are produced only when objects are rubbed. When we rub an inflated balloon with our hair and let it loose, it attaches to wall. This proves that balloon has been charged. Similarly when a glass rod is rubbed with silk, it gets charged.

Charges are of two types : Negative charges and positive charges. Conventionally charge acquired by a glass rod is called positive charges and the charges acquired by the silk with which glass rod is rubbed aquires a negative charge. Similarly charged bodies repel each other and oppositely charged bodies attract each ether.

Question 2.
What is earthing? How is it useful?
Answer:
Transfer of charges to earth through conducting bodies is called earthing. In buildings wiring is done to do earthing when we touch the electric current, it enters the earth through our bodies. The bodies of the living beings including humans are good conductors of electricity. So, they easily acquire charges and transfer them to the earth, if they are in contact of the earth. This is called earthing.

Earthing is very useful as it protects us from electrocution. It prevents electric shocks as it transfers current to the earth. Earthing also saves building from lightning.

Question 3.
How does lightning take place during a thunderstorm?
Answer:
Lightning during thunderstorm takes place due to a phenomenon known as electric discharge. Electric discharge means interaction between oppositely charged objects. During thunderstorms vigorous upward and downward movement of air particles take place. This causes charging of water droplets accumulate in clouds and positive charge accumulates near ground. When these positive charges and negative charges meet a huge amount of energy is released in form of thunder and lightning. This whole process is called electrical discharge.

Question 4.
How can we save ourselves from lightning?
Or
What precautionary measures should be taken to save ourselves from lightning?
Answer:
Lightning gives a warning before appearing. Huge thunder without light is a warning. We should look for a safe place. No place in open is safe.

• One should rush to take shelter in building or house.
• One should not come out of the covered vehicle if on the road.
• One should not keep sitting on open vehicles like scooters, bikes etc.
• One should not take shelter under large and tall trees as they are easy target for electrical discharge.
• One should take shelter under smaller trees while in open as they are not easy target of lightning.
• If in open and no tree or shelter nearabout, one should sit with head folded under arms and embedded between the legs. One should not lie down in open.
• We should plug out all the electrical appliances during lightning.
• We should not use wired telephones during lightning, while mobiles and cordless phones are safe.
• One should not take ones bath during lightning.

Question 5.
What is a lightning rod? How is it used?
Answer:
Lightning rod is a device which is used to save tall buildings from lightning. Tall buildings are easy target to lightning as there can be easy electrical discharge with clouds. Lightning rod is a rod having three spikes on its top and a long earthing- wire to be attached to the earth. The end with spikes is left in open and other end is attached to earth. Lightning rod is fitted on the top of the buildings. During thunderstorm, when electrical discharge takes place between clouds and the building, the lightning rod acquires the charges and transfers them to the earth through its embedded end and saves the buildings from the strike of the lightning.

Question 6.
What is an earthquake? How does it occur?
Answer:
Sudden shaking and trembling of the earth is called earthquake. It occurs due to disturbance deep inside the upper layer of the earth. Earthquake is a natural phenomenon, which can be very devastating depending upon its intensity and magnitude.

The uppermost layer of the earth is not made up of a single flat surface. It is made up of different fragments, called seismic plates. These plates are joined with each other at different points. These plates are always in a continuous motion. Sometimes due to collision of these plates or upward or downward motion of these plates earth starts shaking. This is called an earthquake. The areas falling between these plates are the areas which are the most vulnerable areas for earthquakes. These are called fault zones or in simple language danger zones.

Question 7.
What is a seismograph? How does it work?
Answer:
Seismograph is an instrument which is used to record the intensity of the earthquake. Seismograph has a long rod suspended, with a pen attached to it. A paper is placed under the pen. When an earthquake strikes, the rod starts vibrating. The pen also starts vibrating and paper starts moving under the pen recording the movement of the pen. Scientists further study the seismic waves recorded by pen and make estimates about the intensity of the earthquake. This graph also gives the idea about the energy involved in the earthquake. This idea helps in determining the destructive power of the earthquake.

Some Natural Phenomena Class 8 HBSE Notes

• Natural phenomena like lightning, earthquakes etc. always made people fearful. People had many superstitions regarding these phenomena. They related these phenomenon to wrath and pleasures of Gods.
• Greeks knew that sparks like that of lightning also Occur when amber is rubbed with fur.
• Rubbing the objects with other objects can cause charging like rubbing a plastic scale with hair can charge the scale.
• Similar charged bodies repel each other while oppositely Charged bodies attract each other.
• Charges are of two types : negative and positive.
• Charges on a charged glass rod is said to be positive and other kind of charges are called negative charges.
• Opposite charges attract each other and similar charges repel each other.
• Charges which are generated due to rubbing are called static electricity. Static electricity means where charges do not move as in electric current.
• Charges can be transferred from one body to another. Charges can be transferred from a charged body to earth and this is called earthing.
• Lightning during rain is due to release of huge energy during electric discharge.
• Lightning can be dangerous, but we can secure ourselves by using precautions.
• Lightning rods can protect tall building from lightning as tall objects are easy target for lightning.
• Earthquake is another natural phenomena which can prove disastrous.
• Earthquakes take place due to disturbance in upper crusts of the earth.

Haryana State Board HBSE 8th Class Science Solutions Chapter 16 Light Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 16 Light

HBSE 8th Class Science Light Textbook Questions and Answers

Question 1.
Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room? Explain.
Answer:
We cannot see objects in the room because it is a dark room. No light is reflected from the surfaces of the object, so we are not able to see them. But outside the room, the objects can reflect light thus enabling us to see the objects.

Question 2.
Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?
Answer:
Following are the differences between a regular reflection and diffused reflection :
Regular Reflection:
(i) It takes place on a smooth surface.
(ii) It has all the reflected rays in parallel.
(iii) Reflected rays are in one direction.

Diffused Reflection:
(i) It takes place on a rough surface.
(ii) Reflected rays are not parallel.
(iii) Reflected rays are scattered in different directions.
Diffused reflection is not due to failure of laws of reflection.

Question 3.
Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.
(a) Polished wooden table
(b) Chalk powder
(c) Cardboard surface
(d) Marble stone with water spread over it
(e) Mirror
(f) Piece of paper
Answer:
(a) A polished wooden table will have regular reflection because its surface is smooth.
(b) A chalk powder will ‘get the diffused reflection because chalk particles are not smooth.
(c) Cardbord surface has minute irregularities on it, so it will have a diffused reflection.
(d) Marble stone with water spread over it will have regular reflection if water is stable but if waves are formed then diffused reflection will take place.
(e) A mirror will reflect light regularly due to its smooth surface.
(f) A piece of paper will have irregular reflection due to minute irregularities on it.

Question 4.
State the laws of reflection.
Answer:
Following are the laws of reflection:
(i) Incident ray, reflected ray and normal drawn at the point of incidence to the reflecting surface always lie in the same plane.
(ii) Angle of incidence is always equal to angle of reflection.

Question 5.
Describe an activity to show that the incident rays, the reflected ray and the normal at the point of incidence lie in the same plane.
Answer:
Take a plane mirror and make it stand with help of block on a plane sheet as shown in figure. Now draw an incident line on it AB. Now see in the mirror and mark the points on the paper, where you feel the line is travelling after

getting reflected from the mirror (P₁ and P₂). Now remove the mirror and mark it as OS and Join the points to make the reflected ray. You will see that, it joins the point of incidence, proving that incident ray is the reflected ray (BC).

Question 6.
Fill in the blanks in the following:
(a) A person 1 m in front of a plane mirror seems to _________ be m away from his image.
(b) If you touch your _________ ear with right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with .
(c) The size of the pupil becomes _________ when you see in dim light.
(d) Night birds have _________ cones than rods in their eyes.
Answer:
(a) 2 m
(b) left, left
(c) increase
(d) lesser.

Choose the correct option in the Question 7-8.

Question 7.
Angle of incidence is equal to the angle of reflection:
(i) Always
(ii) Sometimes
(iii) Under special conditions
(iv) Never
Answer:
(i) Always.

Question 8.
Image formed by a plane mirror is:
(a) virtual, behind the mirror and enlarged
(b) virtual, behind the mirror and of the same size as the object
(c) teal at the surface of the mirror and enlarged
(d) real, behind the mirror and of the same size as the object.
Answer:
(b) virtual, behind the mirror and of the same size as the object.

Question 9.
Describe the construction of kaleidoscope.
Answer:
Kaleidoscope is made of three strips of plane mirrors. Three strips of plane mirrors of about 15 cm. length and 4 cm. width are taken and arranged as in a prism i.e. in a triangular form.

They are fixed to each other with thick sheet of paper and enclosed in a tube or in a circular carboard. One end of the tube is covered with a round cardboard disc having a hole in the centre. From the opposite open end some pieces of broken bangles or broken coloured glass are put inside the tube. This open end is also closed. When we see inside this tube through the hole in the circular cardboard; we see different patterns of coloured bangle inside it.

Question 10.
Draw a labeled sketch of human eye.
Answer:

Question 11.
Gurmit wanted to perform Activity 16.8 using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teacher’s advise ?
Answer:
Teacher has advised her to because laser light is harmful for eyes and can cause some permanent damage to eyes when throw directly in eyes.

Question 12.
Explain how you can take care of your eyes?
Answer:
Following precautionary measures can be taken to take care of our eyes:

• We should always wash our eyes with plane cold water atleast three times a day.
• We should not touch our eyes with dirty hands.
• We should never rub our eyes.
• We should not look at Sun directly.
• We should read book, watch T.V., read from black board from a suitable distance.
• Consult an eye specialist if have any irritation, redness in our eyes.

Question 13.
What is the angle of incidence of a ray if the incident and reflected rays is at an angle of 90° to the incident ray?
Answer:
The angle of incidence of the ray will be 45°.

Question 14.
How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?
Answer:
Infinite images will be formed.

Question 15.
Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in the figure. Draw the reflected ray from the second mirror.

Answer:

Question 16.
Bhoojo stands at A just on the side of a plane mirror as shown in figure. Can he see himself in the mirror ? Also can he see image of objects situated at P, Q and R?

Answer:
Bhoojo can’t see himself. He can see the images of objects at P and Q.

Question 17.
(a) Find out the position of the image of an object situated at A in the plane mirror, (figure)
(b) Can Paheii at B see this image?
(c) Can Bhoojho at C see this image?
(d) When Paheii moves from B to C, where does the image of A move?

Answer:
(a) Image will be formed at ‘A’.
(b) Yes, Paheii at B can see the image.
(c) No, Boojho can’t see the image at C.
(d) The image will disappear at Paheii moves from B to C.

Extended Learning – Activities and Projects

Question 1.
Make your own mirror. Take a glass strip or glass slab. Clean it and put it on a white sheet of paper. See yourself in the glass. Next put the glass slab on a black sheet of paper. Again look into the glass. In which case do you see yourself better and why?
Answer:
For self attempt.

Question 2.
Make friends with some visually challenged students. Enquire from them how they read and write. Also find out how they are able to recognise objects, hurdles and currency notes.
Answer:
For self attempt.

Question 3.
Meet an eye specialist. Get your eye sight checked and discuss how to take care of your eyes.
Answer:
For self attempt.

Question 4.
Survery your neighbourhood. Find out how many children below the age of 12 years use spectacles. Find out from their parents what, in their view, could be the reason for the weak eyesight of’ their children.
You can read more on this topic on the following websites :
→ www.glenbrook.k 1 2.il.us/gbssci/phys/ mmedia/optics/ifpm.html
→ www.glenbrook.k 1 2 il.us/gbssci/phys/elass/ refln/u131b.html
Answer:
For self attempt.

HBSE 7th Class Science Light Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is sense of sight?
Answer:
The sense which enables us to see object around us is called sense of sight.

Question 2.
What are the sight organs in animals?
Answer:
Eyes.

Question 3.
What is a mirror?
Answer:
Smooth and shiny surface is called a mirror.

Question 4.
What is reflection?
Answer:
Throwing back the incident light by a plane surface is called reflection.

Question 5.
What kind of surfaces reflect light?
Answer:
All surfaces reflect light.

Question 6.
What is incident ray?
Answer:
Beam of light falling on reflecting surface is called incident ray.

Question 7.
What is reflecting ray?
Answer:
Beam of light reflected back by the reflecting surface is called reflected ray.

Question 8.
What is angle of incidence?
Answer:
Angle formed between the incident ray and normal is called angle of incident.

Question 9.
What is angle of reflection?
Answer:
Angle formed between the reflecting ray and normal is called angle of reflection.

Question 19.
State second law of reflection.
Answer:
Angle of incidence and angle of reflection are always same.

Question 11.
What kind of image is formed by a plane mirror?
Answer:
Virtual and erect image.

Question 12.
Where is the image formed by the mirror?
Answer:
Behind the mirror.

Question 13.
What is the size of the image formed?
Answer:
Same as that on the object infront of the mirror.

Question 14.
At what distance is the image formed behind the plane mirror?
Answer:
At the same distance, as is the object infront of the mirror.

Question 15.
What is the phenomenon called where left side appears to be right and vice- versa in a plane mirror?
Answer:
Lateral inversion.

Question 16.
Which surface shows regular reflection?
Answer:
Smooth surface.

Question 17.
Which surface shews diffused reflection?
Answer:
Rough surface.

Question 18.
What kind of reflection will take place from a polished leather shoes top?
Answer:
Regular reflection.

Question 19.
What kind of reflection will take place from the cover of your note-hook?
Answer:
Diffused reflection.

Question 20.
In what kind of reflection does reflected rays go parallelled to each other?
Answer:
Regular reflection.

Question 21.
In what kind of reflection, reflected rays move scattered?
Answer:
In diffused reflection.

Question 22.
floes Moon has its own light?
Answer:
No.

Question 23.
How does moon shine?
Answer:
It reflected light emitted by the Sun.

Question 24.
Name some objects which have light of their own.
Answer:
Sun, fire, flame of candle etc.

Question 25.
What are objects called, which have light of their own?
Answer:
Luminous objects.

Question 26.
How many mirror strips are used to make a Kaleidoscope?
Answer:
Three.

Question 27.
Is white light a pure white light?
Answer:
No.

Question 28.
How many colours constitute a white beam?
Answer:
Seven.

Question 29.
What is the splitting of white light into its constituent colours called?
Answer:
Dispersion.

Question 30.
What is the shape of human eye?
Answer:
It is roughly spherical in shape.

Short Answer Type Questions

Question 1.
What is reflection of light?
Answer:
When a beam of light falls on a surface, it is thrown back by the surface in a different direction in the same medium. This is called reflection of light. Every surface can reflect. The falling beam of light is called incident ray and beam bouncing back is called the reflected ray.

Question 2.
How do we see various objects?
Answer:
We see various objects due to reflection. As we know all surfaces reflect light, when light falls on any object, it reflects the light. The reflected light reaches our eyes and we are enabled to see the objects.

Question 3.
Write the laws of reflection?
Answer:
There are two laws of reflection :
(i) The ray of incidence, ray of reflection and normal drawn at the point of incidence to the reflecting surface lie in the same plane.

(ii) The angle of reflection and angle of incidence are always equal.

Question 4.
What do you mean by following.
(i) Incident ray
(ii) Reflected ray
Answer:
Incident ray : The light ray that strikes any surface is called incident ray.
Reflected ray : The light ray which is thrown away from the surface after reflection in a different direction, is called reflected ray.

Question 5.
What do you mean by angle of incidence and angle of reflection?
Answer:
The angle formed between the incident ray and the normal is called the angle of incidence. The angle of reflection is the angle formed between the reflected ray and the normal. Both these angles are always equal in size.

Question 6.
What is a mirror? What kind of image is formed in a mirror?
Answer:
Any smooth and shining surface can act as mirror. Mirror is a smooth surface which is polished from its back and can form the image of the object which is placed in front of it. The image formed by a mirror is a virtual and erect image and is of same size as that of the object infront of it.

Question 7.
What is dispersion of light?
Answer:
A beam of white light consists of seven colours. When a beam of white light passes through a prism, it splits into its seven constituent colours. The splitting of white light into its seven constituent colours is called dispersion of light.

Question 8.
How many kind of nerve endings are there in our eyes?
Answer:
There are two types of nerve endings in our eyes. The first type of nerve endings are called cones. Cones are sensitive to bright light and other type of nerve endings are called rods. Rods are sensitive to dim light cones are also sensitive to colours.

Question 9.
How do eye muscle adjust themselves to see the near and distant objects?
Or
What is called the accomodation of eyes?
Answer:
The muscles of the eye contract in order to see near objects. When they contract the lens becomes thicker. When the eye has to see a distant object the muscles expand or relax. This makes the lens thinner. This is called accommodation.

Question 10.
What is the cause of dispersion?
Answer:
Different colours of light bend by different angles of refraction. When light enters the glass prism or a drop of water, different colours bend at different angles and become separated to show phenomenon of dispersion.

Question 11.
How do ciliary muscles affect the functioning of eye?
Answer:
Ciliary muscles can contract and relax. Because of this they can change the thickness of eye lens which also changes its focal length. With change in focal length eye lens can make image of near by objects and also far away objects. So power of accommodation of eye is due to the function of the ciliary muscle.

Question 12.
What is a yellow spot in eyes?
Answer:
Yellow spot or macula is a small area, facing the eye lens. It has high concentration of light sensitive nerve endings or cones. The rest of the retina has lesser cones and more number of cells called rods. It is the spot where brightest vision is formed and colour version is formed.

Question 13.
What is the blind spot?
Answer:
It is a region below the yellow spot, where no light sensitive nerve endings are present. It is an area of no vision.

Question 14.
What is Myopia or short sightedness?
Answer:
This is a type of eye defect, in which person can see nearer objects clearly but cannot see the far off objects. This defect is due to thickness of eye lens. Ciliary muscles do not relax enough to make lens thin enough to see distant objects.

Question 15.
What is Hypermetropia or long sightedness?
Answer:
This is a type of an eye defect, in which the person can see far off objects clearly, but cannot see the nearer objects. This defect is due to thinness of the eye lens. The ciliary muscle do not contract enough to make the lens see nearer objects.

Question 16.
What is cataract? How can it be corrected?
Answer:
During old age, the eye sight becomes blurred. It happens because the lens of the eye becomes opaque and milky. When the vision becomes cloudy the person is said to have cataract. It is possible to treat this temporary loss of vision by removing the opaque lens and, a new artificial lens is inserted by minor and simpe operation.

Question 17.
Write any three safety measures to protect our eyes.
Answer:

• We should not rub our eyes.
• We should wash our eyes many times a day.
• We should not look at sun or other powerful lights directly.

Question 18.
What is Braille system?
Answer:
Braille is based on code of one to six dots which are raised. Each dot has a position. These dots make up letters of alphabet, number and all other things done in print. Any language can be read through the codes of the braille by touching the dots.

Long Answer Type Questions

Question 1.
What is reflection of light? State laws of reflection.
Answer:
Reflection of light is throwing back of light by any object. When a beam of light falls on some surface, the surface throws that beam away in different direction. This is called reflection of light. Following are the laws of reflection:

(a) When a ray of light falls on a reflecting surface, it is reflected in such a way that the angle of incidence is equal to the angle of reflection i.e. ∠i = ∠r.

(b) The incident ray, the normal and the reflected ray, all lie in the same plane.

Question 2.
What are the characteristics of image formed with a plane mirror?
Answer:
Plane mirror is a shiny, polished surface. When any object is placed in front of the mirror, an image is formed. Following are the characteristics of the image formed by a plane mirror:

• Image formed on a plane mirror cannot be taken on a screen, such image is called a virtual image.
• Image formed on a plane mirror is erect.
• It is laterally inverted i.e. left hand of the object appears as the right hand.
• Image formed is as far behind as the object is in front of it.

Question 3.
What are the uses of a plane mirror?
Answer:

• We use a plane mirror to see our reflections in it, at our homes.
• Plane mirrors are used to reflect light on a particular object.
• Plane mirrors are used for signalling by scouts and army.
• They are used to form multiple images in show windows.
• Plane mirror is used to reflect sun rays in appliances like solar cooker etc.
• Toys like Kaleidoscope are made on the concept of multiple reflection. Navy use periscopes based on concept of multiple reflection for spying in sea.

Question 4.
Describe how does human eye work?
Answer:
The light reflected by objects enter our eyes through cornea. That is why cornea is called window to the world. Lens focuses the image of the object on the retina. Retina converts these optical images into optical pulses. These optical pulses are then sent to brain through optical nerves. The amount of light entering the eye through cornea is controlled by Iris. It expands when light is bright and thus enables the pupil to enter controlled amount of light to enter the eye. In dark it contracts and increases the size of pupil to allow more light to enter the eye.

The retina forms a small and inverted image of the object. The brain interprets it and forms the erect and correct sized image.

Question 5.
Write various measures to save our eyes.
Answer:
Eyes are a precious gift of God. We should take proper care of our eyes and protect them from injury. Following measures should be taken for healthy eyes :

• We should wash our eyes with cold water everyday and wipe them with clean and soft cloth.
• We should never rub our eyes. If some particle enters our eyes, we should wash our eyes with cold water.
• We should always read in proper light.
• In case of any injury or other problems related to eyes, we should avoid self medication and immediately consult an eye specialist.

Question 6.
What is blindness? How many types of blindness do we know about?
Answer:
A person is said to be blind or visually impaired when he or she is imable to see. Blindness is of two types:
Curable Blindness : When cornea becomes opaque or the lens becomes opaque the sight of the person becomes decreased. This is called a temporary or curable blindness. In this case the person is operated upon and sight is resorted. An artificial lens is inserted in place of opaque lens and the opaque cornea is replaced with a healthy donated cornea.

Permanent Blindness : In this type of blindness image formed by cornea is not transferred to brain and this type of blindness cannot be cured.

Pollution of Air and Water Class 8 HBSE Notes

• We see all the things around us only due to sense of sight.
• Eyes are our organs of sight, which enables us to see objects around us.
• It is the light which enables our eyes to see the objects. Without light our eyes cannot sense anything.
• Any polished or shiny surface acts as a mirror. It can change the direction of light.
• Light is reflected from all the surfaces.
• When a beam of light falls on a surface, it throws back the light to same medium. This phenomenon is called reflection of light.
• The beam of light falling on the plane surface is called the incident ray.
• The beam of light thrown back by the reflecting surface is called the reflected ray.
• The line drawn between the point where the incident ray and reflected ray meet is called the normal.
• The angle between the normal and the incident ray is called angle of incidence.
• The angle between the normal and the reflected ray is called the angle of reflection.
• The angle of incidence and the angle of reflection are equal.
• Incident ray, reflected ray and the normal drawn at the point of incidence to reflecting surface lie in the same plane.
• Above two points are called laws of reflection.
• Light falling on a smooth surface is reflected regularly.
• Irregular or diffused reflection takes place on rough surface.
• In mirror the right appears as left and left as right. This is called lateral inversion.
• Two mirrors inclined to each other at different angles, give multiple images.
• White light consists of seven colours called spectrum.
• Splitting of white light into its constituting seven colours is callled dispersion.
• Our eyes have different parts which perform different functions to enable us to see the objects.
• Visually challenged persons can read and write using Braille system.

Haryana State Board HBSE 8th Class Science Solutions Chapter 4 Materials: Metals and Non-Metals Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 4 Materials: Metals and Non-Metals

HBSE 8th Class Science Materials: Metals and Non-Metals Textbook Questions and Answers

Question 1.
Which of the following can be beaten into thin sheets?
(a) Zinc
(b) Phosphorus
(c) Sulphur
(d) Oxygen
Answer:
(a) Zinc.

Question 2.
Which of the following statements is correct?
(a) All metals are ductile.
(b) All non-metals are ductile.
(c) Generally, metals are ductile.
(d) Some non-metals are ductile.
Answer:
(a) All metals are ductile. ✗
(b) All non-metals are ductile. ✗
(c) Generally, metals are ductile. ✓
(d) Some non-metals are ductile. ✗.

Question 3.
Fill in the blanks:
(a) Phosphorus is very ……….. non-metal.
(b) Metals are ……….. conductor of heat and ………….. .
(c) Iron is ………….. reactive than copper.
(d) Metals react with acids to produce ………….. gas.
Answer:
(a) reactive
(b) good, electricity
(c) less
(d) hydrogen.

Question 4.
Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) Generally, non-metals react with acids. ( )
(b) Sodium is a very reactive metal. ( )
(c) Copper displaces zinc from zinc sulphate solution. ( )
(d) Carbon can be drawn into wires. ( )
Answer:
(a) False
(b) True
(c) False
(d) False.

Question 5.
Some properties are listed in the following table. Distinguish between metals and non-metals on the basis of their properties.

Answer:

Question 6.
Give reasons for the following:
(a) Aluminium foils are used to wrap food items.
(b) Immersion rods are made up of metallic substances.
(c) Copper cannot displace zinc from its salt solution.
(d) Sodium and potassium are stored in kerosene.
Answer:
(a) Aluminium foils are used to wrap food items because aluminium can be beaten in sheets to form these thin wrapping sheets and it is soft and it does not react with food items.

(b) Immersion rods are made up of metallic substances because metals are good conductors of heat and electricity. They get hot very soon on passage of current and warm the water.

(c) Copper cannot displace zinc from its salt solution because copper is less reactive than zinc. A less reactive metal cannot displace a more reactive metal from its solution.

(d) Sodium and Potassium are stored in kerosene because they are very reactive and quickly react in air.

Question 7.
Can you store acidic lemon pickles in an aluminium utensils? Explain.
Answer:
No, we cannot store acidic lemon pickles in aluminium utensils because aluminium is a metal. Metals readily react with acids to produce hydrogen gas. So, when the aluminium metal comes in contact with acidic lemon pickles, it would react to release hydrogen, which would spoil the food and render it unfit to consume.

Question 8.
In the following table some substances are given in Column I. In Column II some uses are given. Match the items in Column I with those in Column II.

Answer:

Question 9.
What happens when:
(i) Dilute sulphuric acid is poured on a copper plate?
(ii) Iron nails are placed in copper sulphate solution?
Write word equations of the reactions involved.
Answer:
(i) When sulphuric acid is poured on copper plate the acid present in sulphuric acid reacts with copper to form copper sulphate and hydrogen. The copper plate gets eroded from place.
Sulphuric Acid + Copper → Copper Sulphate + Hydrogen
(ii) When iron nails are placed in copper sulphate solution the iron being more reactive will replace copper in its salt solution,
(Ferrous Sulphate) → Iron + Copper Sulphate → Iron Sulphate + Copper
The solution will turn light green.

Question 10.
Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.
(i) How will she find the nature of the gas?
(ii) Write down equations of all the reactions taking place in this process.
Answer:
(i) She will test it with litmus paper to check the acidic or basic nature of gas. If red litmus turns blue, it is basic in nature. If blue litmus turns red, it is acidic in nature.

(ii) Sulphur dioxide (SO₂) + Water (H₂O) → Sulphurous acid (H₂SO₃).

Question 11.
One day Reeta went to a Jeweller’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back they found that there was a loss in its weight. Can you suggest a reason for the loss in weight?
Answer:
When gold is washed in acidic solution, it being a metal reacts with acid and forms the hydrogen gas with some metallic oxides. This causes the loss of gold in form of gold oxides. This looses the weight of gold.

Activity.

No. 4.1. Malleability Of Materials

No. 4.3. Electrical Conductivity Of Materials

Extended Learning – Activities And Projects

Question 1.
Prepare Index Cards for any four metals and non-metals. The card should have information like name of metal/non-metal; its physical properties, chemical properties and uses.
Answer:
1. Name of metal: Copper
Physical properties:
(i) It is hard
(ii) It is ductile.
(iii) It is good conductor of heat and electricity.

Chemical Properties:
(i) Copper reacts with moist air to form greenish coating.
(ii) It oxide is basic in nature.
(iii) It reacts with acids to produce hydrogen gas.
(iv) It displaces iron from iron sulphate solution.

Uses:
Copper is used to make electrical wires, base of cooking utensils, etc.

Non-metals:

2. Name of non-metal: Coal
Physical properties:
(i) It is not ductile.
(ii) It is not malleable.
(iii) It is hot sonorous and does not shine. It is soft.
(iv) It is poor conductor of electricity

Chemical Properties:
(i) It produces oxides of carbon when burnt
(ii) It’s oxide are acidic in nature.
(iii) It does not take part in replacement reaction.

3. Name of Non-metal: Sulphur
Physical properties:
(i) It is neithre ductile nor malleable.
(ii) It is soft and dull.
(iii) It is poor conductor of heat and electricity.

Chemical properties:
(i) It reacts with oxygen to produce sulphur dioxide.
(ii) It reacts with water to form sulphurous acid H₂SO₄ which is acidic in nature.
(iii) Metals are heated to mould them.
(iv) Gold is preferred to prepare jewellary because it is less reactive ductile and is a costly metal.

4. Name of Metal: Iron
Physical properites:
1. malleable
2. non-ductile
3. sonorous
4. hard
5. good conductor of heat and current.

Chemical properties:
1. React with oxygen to form rust.
2. React with water.
3. React with acids to form hydrogen gasi
4. React with sodium hydroxide to produce hydrogen gas.

Uses:
Used to make machines, tools, door, etc.

Question 2.
Visit a blacksmith and observe how metals are moulded.
Answer:
For self attempt.

Question 3.
Suggest an experiment to compare the conductivity of electricity by iron, copper, aluminium and zinc. Perform the experiment and prepare a short report on the results.
Answer:
For self attempt.

Question 4.
Find out the locations of the deposits of iron, aluminium and zinc in India. Mark these in an outline map of India. In which form are the deposits found? Discuss in the class.
Answer:
For self attempt.

Question 5.
Discuss with your parents / neighbours / goldsmiths why gold is preferred for making jewellery.
Answer:
For self attempt.

Question 6.
Visit the following websites and enjoy the quiz on metals and non-metals.

• chemistry.about.com /library/weekly/ bl05030a.htm
• chemistry.about.com / od / testsquizzes / Chemistry_Tests_Quizzes.htm.
• www.syvum.com / cgi / online / mult.cgi / squizzes / science / metals.tdf?0
• www.gcsescience.com / q / quesemet.html
• www.corrosionsource.com / handbook / periodic / metals.htm
  Answer:
  For self attempt.

HBSE 8th Class Science Materials: Metals and Non-Metals Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is meant by malleability of a metal?
Answer:
The property by virtue of which a metal can be hammered into thin sheets is called malleability.

Question 2.
What is meant by ductility of metals?
Answer:
Ductility of metals means that they can be drawn into very thin wires.

Question 3.
Name two metals which are both malleable and ductile.
Answer:
Gold and silver.

Question 4.
Are non-metals malleable and ductile?
Answer:
No.

Question 5.
Name a metal which exists in liquid state.
Answer:
Mercury.

Question 6.
Name the hardest substance in the world.
Answer:
Diamond.

Question 7.
Which metal is the best conductor of electricity?
Answer:
Silver.

Question 8.
Identify the most reactive and the least reactive metal amongst the following:
Al, K, Cu, Au.
Answer:
K is the most reactive while Au is the least reactive metal.

Question 9.
Name the metal which is stored in kerosene oil.

Answer:
Sodium is stored in kerosene oil.

Question 10.
Which metal foil is used in packing of some medicine tablets?
Answer:
Aluminium.

Question 11.
Which metal foil is used for decorating sweets?
Answer:
Silver.

Question 12.
Name a non-metal which is good conductor of heat.
Answer:
Graphite.

Question 13.
Why do gold and silver exist in free state?
Answer:
Gold and silver exist in free state because they are less reactive.

Question 14.
What would happen to the iron railings in open, when not painted?
Answer:
They will be rusted.

Question 15.
Why electric wires are made of copper?
Answer:
Electric wires are made of copper because it is good conductor of electricity.

Question 16.
Iron nails are kept dipped in blue copper sulphate solution and solution gets changed into light green colour. Why?
Answer:
This happens because iron displaces copper to form Ferrous Sulphate which is light green in colour.

Question 17.
Explain why silver does not displace hydrogen from dil HCl?
Answer:
Silver is less reactive than hydrogen, so it does not displace hydrogen from dil HCl.

Question 18.
When does red litmus paper turn blue?
Answer:
When red litmus paper comes in contact with basic solution.

Question 19.
When does a blue litmus paper turn red?
Answer:
Blue litmus paper turns red when it comes in contact with acidic solution.

Question 20.
What happens when sulphur dioxide gets dissolved in water?
Answer:
Sulphurous acid is formed:
SO₂ + H₂O → H₂SO₃

Question 21.
Oxides of non-metals are generally of which nature?
Answer:
Oxides of non-metals are generally of acidic nature.

Question 22.
What happens when sodium comes in contact with water?
Answer:
Sodium catches fire and heat is released.

Question 23.
How do non-metals react with water?
Answer:
Non-metals do not react with water.

Question 24.
How do non-metals generally react with acids?
Answer:
Non-metals generally do not react with acids.

Question 25.
Which gas is emitted when metals react with acids?
Answer:
Hydrogen gas.

Question 26.
Write any use of non-metal.
Answer:
Non-metals are used in crackers.

Question 27.
Write any use of metals.
Answer:
Metals are used to make all means of transportation.

Question 28.
What is a displacement reaction?
Answer:
Reaction in which a more reactive metal displaces the less reactive metal from its compound in aqueous solution is called displacement reaction.

Short Answer Type Questions

Question 1.
Write any three physical characteristics of metals.
Answer:
(i) Metals can be hammered to make sheets so they are malleable.
(ii) Metals can be drawned into very thin wires, that means metals are ductile.
(ii) Metals are good conductors of heat and electricity.

Question 2.
Write any three physical characteristics of non-metals.
Answer:
(i) Non-metals are non-ductile and non- malleable.
(ii) Non-metals are non-sonorous.
(iii) Non-metals are poor conductors of heat and electricity.

Question 3.
What do you mean by sonorous materials?
Answer:
Materials which make a sound when they are hit hard with some other material are called sonorous materials. All metals except the soft ones are sonorous, while all non-metals are non-sonorous.

Question 4.
How do metals and non-metals react with oxygen?
Answer:
Metals react with oxygen to form oxides generally. These oxides are alkaline.
\(\begin{array}{ccc}
2 \mathrm{Mg} & +\mathrm{O}_{2} \rightarrow & 2 \mathrm{MgO} \\
\text { Magnesium } & \text { Oxygen } & \text { Magnesium oxide }
\end{array}\)
Non-metals also react with oxygen to form oxides but these oxides are acidic in nature.
\(\begin{array}{cc}
\mathrm{C} & \mathrm{O}_{2} \\
\text { Carbon } & \text { Oxygen }
\end{array} \quad \rightarrow \quad \mathrm{CO}_{2}\)

Question 5.
A copper coin is kept immersed in a solution of silver nitrate for some time. What will happen to the coin and the colour of the solution?
Answer:
Copper is more reactive than silver. Therefore, when a copper coin is kept immersed in a solution of silver nitrate, it will displace silver from silver nitrate solution and a solution of copper nitrate will be formed.
Thus, the copper coin will dissolve in the solution and the colour of the solution will change from colourless to blue.

Question 6.
Explain why zinc metal can displace copper from copper sulphate solution but copper cannot displace zinc from zinc sulphate solution.
Answer:
Zinc metal is more reactive than copper. Therefore, it can displace copper from CuS0₄. Cu is less reactive than Zn, therefore, cannot replace Zn from ZnS0₄.

Zn + CuSO₄ → ZnSO₄ + Cu

Question 7.
State any three reasons for counting sulphur amongst the non-metals.
Answer:
Sulphur is a non-metal because:
(i) It is neither malleable nor ductile.
(ii) It does not conduct heat and electricity.
(iii) It combines with oxygen to form acidic oxide.

Question 8.
Non-metals do not react with water. How does this fact is utilized to store very reactive non-metals?
Answer:
Non-metals do not react with water. This quality is quite helpful in protecting some highly reactive non-metals which quickly react in air. Phosphorus is very reactive non-metal. It immediately catches fire when exposed to air. To prevent this, it is stored in water.

Question 9.
What is an element?
Answer:
Element is the smallest unit of any material. It cannot be broken further by cooling, heating or by electrolysis e.g. sulphur, iron, carbon etc.

Question 10.
Compare the physical properties of metals and non-metals.
Answer:

Question 11.
Compare the chemical properties of metals and non-metals.
Answer:

Question 12.
In which state do metals occur inside the earth’s crust?
Answer:
Metals occur in different states inside the earth’s crust depending upon their reactivity. Some metals occur in elemental state or in the form of compounds. Reactive metals generally are found in compound. Highly unreactive metals occur in free state while the less reactive metals can either be found in combined state or infree state.

Question 13.
What do you mean by Malleability of metals.
Answer:
The physical property of metals by virtue of which metals can be beatan into thin sheet is called malleability. Most of the metals are malleable. Aluminium is beaten into aluminium foil for wrapping food and silver is also beaten to make silver foils to decorate sweets.

Question 14.
What do you mean by ductility?
Answer:
The physical property by virtue of which metals can be drawn into thin wires is called ductility. Metals which are good conductors of electricity are mostly drawn into wire to be used in electrical cables. Gold and silver are the most ductile metal. Wires of copper, aluminium and tungsten are used to make electricity cables and tungsten is used to make filaments of bulbs. Aluminium wires are also widely used to make electrical wires.

Question 15.
What is an alloy? Describe any one alloy.
Answer:
Mixture of two or more than two metals to get desired qualities is called an alloy. Stainless steel is an alloy of iron, chromium and nickel. It is used to make utensils, surgical & instruments and many other decorative items. Stainless stell is hard and do not rust.

Long Answer Type Questions

Question 1.
Write a short note on displacement reaction of metals.
Answer:
A more reactive metal displaces a less reactive metal from its compound in an aqueous solution. This is called displacement reaction. For example, when some iron nails are dipped in copper sulphate solution, the iron being more reactive displaces copper from its solution and form ferrous sulphate solution of light green colour.

Similarly, magnesium and zinc also displaces copper from its compound.

Question 2.
How will you prove the nature of rust or the ash obtained from burning magnesium ribbon?
Answer:
This can be easily proved in laboratory. Take some rust and dissolve it in water (a few drops). Now take a red litmus paper and dip the litmus paper in solution. We will see that the red litmus paper turns blue.

When the red litmus paper turns blue it means solution is basic in nature. So the rust is basic in nature. We can similarly check the nature of ash obtained by burning a magnesium ribbon. It will also turn red litmus paper blue proving its basic nature.

Question 3.
How do different metals react with water?
Answer:
Different metals react differently with water, hydrogen being a common end product.
Sodium metal reacts vigorously with water to form sodium hydroxide and hydrogen gas.

Magnesium only reacts with hot boiling water to form magnesium oxide and hydrogen.

Red hot iron reacts with steam to form iron oxide and hydrogen copper. Silver and nickel do
not react with water.

Question 4.
What are the different uses of metals?
Answer:
Metals are very useful to us. Some of the uses of common metals are following:
(а) Copper and aluminium metals are used to make electric wires. This is because copper and aluminium are good conductors of electricity.
(b) Copper, aluminium and iron metals are used for making utensils and other domestic things. These metals are also used to make various factory equipments. This is because, all these metals are good conductors of heat.
(c) Iron is used to make heavy machinery and is also used in construction of buildings because it is very heavy and strong.
(d) Thin foils of aluminium are used in packaging food materials and medicines etc.
(e) The liquid metal mercury is used in thermometers.
(f) Gold and silver metals are used to make jewellery.
(g) Sodium, titanium and zirconium metals are used in atomic energy and space projects.

Question 5.
What are the different uses of non-metals?
Answer:
Following are the uses of non-metals:
(a) Oxygen is used by plants and animals for respiration. Oxygen also supports the process of combustion in factories, houses, aeroplanes
and missiles.
(b) Compounds of nitrogen provide nutrients to soil and plants. Fertilizers made by using nitrogen are extensively used in agricultural practices.
(c) Chlorine is used to disinfect the drinking water as it has the ability to kill germs.
(d) Sulphur is also used as germicide, it is also used as an antiseptic fcr skin treatment (in ointments).
(e) Non-metals are used in crackers.

Question 6.
What is corrosion? How does it affect different metals?
Answer:
Corrosion is defined as attack of atmospheric gases and moisture on the surfaces of metal making them deformed and weak. If iron is left in open for a period of time, it slowly gets deposits of brown flakes on it, which is called rusting of iron. It is undesirable because it makes the iron weak and eat it up slowly with passage of time. Similarly silver objects become black in colour and loose their lustree as silver reacts with hydrogen sulphide gas of air. Slowly the copper vessels also get coated with greenish layer of copper carborate. It is formed due to reaction of copper with carbondioxide of air and water vapour also present in air.

Question 7.
Write composition, properties and uses of following alloys: Steel, Stainless Steel, Brass and Duralumin
Answer:

Materials: Metals and Non-Metals Class 8 HBSE Notes

1. All metals and non-metals have some physical and chemical properties which differentiate them from each other.
2. Properties related to appearance and structure are called physical properties while how they react with other metals and non-metals are called their chemical properties.
3. Metals are shiny in appearance. This property of metals is called lustre.
4. Metals are generally hard. Sodium and potassium are soft. All metals mostly exist in solid state except murcury which is a liquid at room temperature.
5. Metals can be beaten with hamrqer and can be beaten into sheets. This physical property of metals is called malleability. Most of the metals are malleable.
6. Metals can be drawn into wires, they are thus ductile . Gold, tungsten are highly ductile metals.
7. Metals are good conductors of heat and electricity. That is why metals are used to make electric wires and most of the cooking utensils are made of metals. Silver is the best conductor of electricity.
8. Metals make sound, when they are hit hard with other object. This property makes them sonorous.
9. Non-metals do not shine and break-up when hit hard with hammer.
10. Non-metals cannot be beaten into sheets.
11. Non-metals cannot be drawn into wires.
12. They do not make any sound when hit with other objects.
13. Non-metals are bad conductors of heat and electricity.
14. Metals and non-metals react with oxygen to form oxides. Metal oxides are alkaline and oxides of non-metals are acidic in nature.
15. Metals react with water at different rates to form oxides and hydrogen gas. Non-metals do not react with water except sodium and magnesium.
16. Non-metals generally do not react with acids but metals react to produce hydrogen gas.
17. A more reactive metal displaces the less reactive metal from its compound in aqueous solution.
18. Metals and non-metals are very useful to us. They are used for different purposes.
19. All the materials can be divided into metals, non-metals and metalloids on the basis of above discussed physical mid chemical properties. Metalloids are those materials which possess the qualities of both metals and non-metals.

Haryana State Board HBSE 8th Class Science Solutions Chapter 3 Synthetic Fibres and Plastics Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 3 Synthetic Fibres and Plastics

HBSE 8th Class Science Synthetic Fibres and Plastics Textbook Questions and Answers

Question 1.
Explain why some fibres are called synthetic?
Answer:
Some fibres are called synthetic because they do not occur naturally and are made by man using petrochemicals.

Question 2.
Mark (✓) the correct answer:

Rayon is different from synthetic fibre because
(i) it has a silk like appearance
(ii) it is obtained from wood pulp
(iii) its fibres can also be woven like those of natural fibres.
Answer:
(ii) it is obtained from wood pulp. ✓

Question 3.
Fill in the blank with appropriate words:
(i) Synthetic fibres are also called ……………. or ……………. fibres.
(ii) Synthetic fibres are synthesised from raw material called ……………. .
(iii) Like synthetic fibres, plastic is also a ……………. .
Answer:
(i) man-made or artificial fibres
(ii) petrochemicals
(iii) polymer.

Question 4.
Give examples which indicate that nylon fibres are very strong.
Answer:
Nylon fibres are very strong, thus they are used to prepare ropes for mountaineering. They are also used to prepare parachutes.

Question 5.
Explain why plastic containers are favoured for storing food.
Answer:
Advantanges of storing foods in plastic containers are:
(a) the plastics do not react with the food stored in them.
(b) the plastics are light weight and are strong.
(c) they are easy to handle and safe.

Question 6.
Explain the difference between the thermoplastic and thermosetting plastics.
Answer:
Differences between thermoplastic and thermosetting plastics:
(i) Thermoplastics can be mtelted on heating but thermosetting plastics Cannot be melted.
(ii) Thermoplastics can be reshaped as many times as desired but thermosetting plastics cannot.
(iii) Thermoplastics can be bent but thermosetting plastics cannot be bent.
(iv) Thermoplastics are good conductors of heat, thermosetting plastics are bad conductors of heat.

Question 7.
Explain why the following are made of thermosetting plastics:
(a) Saucepan handles
(b) Electric plugs/switches/plug boards.
Answer:
(a) The handles of saucepan are made of thermosetting plastic because it is a bad conductor of heat and do not get heated up while cooking. So it becomes easy to handle the utensil while cooking.
(b) Electric plugs/ switches and plug boards are made up of thermosetting plastic because it is a bad conductor of electricity. It does not allow the electric current to pass through it, thus safe in using in electric appliances.

Question 8.
Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’.
Telephone instruments, toys, cooker handles, carry bags, ball point pens, plastic bowls, electric wire covering, plastic chairs, electrical switches.
Answer:
Can be Recycled: Toys, carry bags, plastic bowls, ball point pen, plastic chairs, electric wire covering.
Cannot be Recycled: Cooker handles, electric switches, telephone instruments.

Question 9.
Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Answer:
Cotton clothes are preferred to synthetic clothes in summers because cotton is a bad conductor of heat. It does not allow the outer heat to enter in our body, thus protects body from heat. It also has more capacity to hold moisture than the synthetic clothes. So, it retains
the sweat of the body and keeps it cool. So, Rana should buy shirts made upof cotton.

Question 10.
Give examples to show that plastics are noncorrosive in nature?
Answer:
Following examples show that plastics are non-corrosive in nature:
(i) They are used to store chemicals in laboratories.
(ii) They are used to store all types of food, as it does not react to materials stored in it.
(iii) It does not even react with air and water.

Question 11.
Should theiiandle and bristles of a tooth brush be made of the same material? Explain your answer.
Answer:
No, the handle and bristles of a tooth brush should not be made of the same material because the bristles should be soft and the handle should be hard. So the bristles should be made up of soft material so that it does not harm the gums. The handles should be made up of hard material so that it can give firm grip.

Question 12.
‘Avoid plastics as far as possible,’ Comments on this advice.
Answer:
Plastics are harmful for our environment. Some of the plastics cannot be recycled, so they cannot be used again and thus cannot be finally disposed off. They thus, should be avoided as far as possible.

Question 13.
Match the terms of column I correctly with the phrases given in column II:

Answer:

Question 14.
‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.
Answer:
Manufacturing synthetic fibres is actually helping conservation of forests because it does not require cfutting plants and hunting animals to get the natural fibres. The synthetic fibres are made up of chemicals and these chemicals are not available in forests.

Question 15.
Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer:
Observe all the electric wires of your house from a distance. You can take an electric wire which is not carrying current. Open the main wire you will see three/two small wires in the main wire and will see that they have covering of red, green and yellow plastic covering. This proves that the thermoplastics are bad conductors of electricity.

Extended Learning – Activities And Projects

1. Have you heard of the campaign: “Say No To Plastics”. Coin a few ihore slogans of this kind. There are certain governmental and non-governmental organisations who educate general public on how to make a wise use of plastics and develop environment friendly habits. Find, out organisations in your area which are . carrying out awareness programmes. If there is none, form one. .
Answer:
For self attempt. .

2. Organise a debate in the school. The children may be given an option to rule play as manufacturers of synthetic fabrics or those of fabrics from natural sources. They ican then debate on the topic “My Fabric is Superior.”
Answer:
For self attempt.

3. Visit five families in your Neighbourhood and enquire about the kind of clothes they use, the reason for their choice and advantages of using them in term: of cost, durability and maintenance. Make a short report and submit it to your teacher.
Answer:
For self attempt.

4. Devise an activity to show that organic waste is biodegradable while plastic is not.
Answer:
Take some organe peels or peels of any fruit or vegetable. Now take any broken object of plastic.
Take two flower pots. In one pot dig a small pit and throw peels and cover it with mud. In second pot put the plastic and cover it with mud. Observe them after 5-10 day, and you will see that the peels have started decomposing and nothing has happened to plastic toy.

5. If you wish to know more about fibres and plastics and the products made from them, you may explore the following web sites:
• http://www.pslc.ws/macrog/index.htm
• http://www.edugreenteri.res.in/ exploresolwaste/types/htm
• http://www.nationalgeographic.com/ resouces/ngo/eduction/plastics
• http://www.packagingtoday.com/
• http://www.bbc.co.uk/schools.gcsebitesize/ design/textiles/fibresrev/html/

HBSE 8th Class Science Synthetic Fibres and Plastics Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Why do we wear clothes?
Answer:
We wear clothes to get protected from heat, cold and other outer conditions.

Question 2.
How many types of fibres are there?
Answer:
There are two types of fibres: Natural fibre and Synthetic fibres.

Question 3.
What are natural fibres?
Answer:
Fibres obtained from animals and plants are called natural fibres.

Question 4.
What are synthetic fibres?
Answer:
Fibres made of chemicals by the man are called synthetic fibres.

Question 5.
Name some natural fibres.
Answer:
Silk, wpol, cotton, jute, etc.

Question 6.
Name some synthetic fibres.
Answer:
Nylon, rayon, polyester, Acrylic.

Question 7.
What are polymers?
Answer:
Polymers are small jinits which combindfo make a synthetic fibre.

Question 8.
Name one natural polymer.
Answer:
Cellulose is a polyiper of cotton.

Question 9.
Which synthetic fibre is called synthetic silk?
Answer:
Rayon.

Question 10.
Which country discovered silk for the first time?
Answer:
China.

Question 11.
Which raw material is used to make rayon?
Answer:
Wood pulp.

Question 12.
Which raw material is used to make Nylon?
Answer:
Coal, water and air.

Question 13.
Name few items made from nylon.
Answer:
Socks, ropes, tents, sleeping bags, parachutes, etc.

Question 14.
Which is the strongest synthetic fibre?
Answer:
Nylon.

Question 15.
Which synthetic fibre can be stronger than a steel wire?
Answer:
Wire made of nylon.

Question 16.
Name a synthetic fibre which works like wool.
Answer:
Acrylic.

Question 17.
What happens when synthetic fibre is burnt?
Answer:
It starts melting.

Question 18.
What are petrochemicals?
Answer:
Petrochemicals are raw materials processed to make synthetic fibres.

Question 19.
Name a few properties of plastics.
Answer:
They can be moulded, recycled, reused and melted.

Question 20.
What use polythene is put to?
Answer:
Polythene is used to make carry bags.

Question 21.
What do we call the plastics which can be remoulded again and again?
Answer:
Thermoplastics.

Question 22.
What do we call the plastics, which cannot be remoulded and reused?
Answer:
Thermosetting plastics.

Question 23.
Why electric switches and plugs are made of plastics?
Answer:
They are resistant to electricity.

Question 24.
Which material is used to make non-stick utensils?
Answer:
Teflon.

Question 25.
Which material is used to make the handles of the cookware?
Answer:
Melamine.

Question 26.
What makes plastic a wonder material?
Answer:
Lightness, strength, durability and non-reactiveness.

Short Answer Type Questions

Question 1.
Distinguish between Natural fibre and Synthetic fibre.
Answer:
Natural fibres are obtained from natural resources like plants and animals e.g., cotton, jute, etc. are obtained from plants. Silk and wool are obtained from animals. Synthetic fibres are made from synthetic materials, like petrochemicals, e.g. Nylon, Terelene, acrylic etc.

Question 2.
Why silk is so costly?
Answer:
Silk is a natural fibre obtained from silk moth. It takes a lot of time and efforts to make silk. So, it costs high.

Question 3.
What is Polyester?
Answer:
Polyester is the word coined by joining ‘poly’ and ‘ester’. This synthetic fibre is made by joining many ester units. Ester is a chemical which causes smell in fruits.

Question 4.
What makes acrylic more popular than pure wool?
Answer:
Acrylic is a synthetic fibre. It resembles wool in looks and in qualities. Wool is expensive becuse it is obtained from natural sources but acrylic is cheaper and is available in vibrant colours. It is more durable than wool.

Question 5.
What is the main disadvantage of synthetic fibre?
Answer:
Synthetic fibres are good conductors of heat. They melt when heated. This causes a great danger for the user. In case the fibre catches fire while working in the kitchen, it will stick to the user’s body and will cause great damage to skin.

Question 6.
Which fibre will you prefer to get your raincoat stitched? Why?
Answer:
We will prefer synthetic fibre for getting our raincoat stitched because it will not absorb much amount of water and dispell it saving us from rain water. It will also dryup soon later.

Question 7.
How can polythene carry bags be harmful for animals?
Answer:
Polythene carry bags are thrown here and there after using them. Stray cattle consume them. In this case, it can choke the respiratory system and damage their stomach. It can even cause their death.

Question 8.
What are thermoplastics? Explain with examples.
Answer:
Those plastics which can melt on heating and which can be reshaped on moulding again and again are called thermoplastics P.V.C., Polythene are examples of thermoplastics. Toys, containers, car grills, combs etc. are made with thermoplastics.

Question 9.
What are thermosetting plastics?
Answer:
Thermosetting plastics are those plastics, which can be only moulded for once. They cannot be reshaped or reused because they do not get softened op heating. Bakelite, melamine etc. are examples of thermosetting plastics.

Question 10.
What are biodegradable and non-biodegradable materials?
Answer:
Biodegradable substances are those substances which can be decomposed by bacteria and other natural processes. Those substances which cannot be decomposed are called non-biodegradable substances. Plastics are non-biodegradable.

Long Answer Type Questions

Question 1.
Distinguish between natural fibres and synthetic fibres.
Answer:

Question 2.
Name different artificial fibres and write their uses.
Answer:
Following are the main synthetic fibres:
(i) Rayon:
It is also called the artificial silk as it has great lustre and is fight in weight. It is obtained by the chemical treatment of wood pulp. It can be woven like silk and dyed in different colours. It is used as dress material. Mixed with cotton, it is used to make curtains, bedsheets etc. It is mixed with wool to make beautiful carpets.

(ii) Nylon:
It is the strongest fibre. It is made by coal, water and air. It is elastic in nature and fight in weight. It is lustrous and thus ideal for making dresses. It is also used to make stockings, seat belts, ropes, tents, toothbrushes, sleeping bags, curtains and parachutes, etc.

(iii) Polyester:
It is made up of multiple units of ‘esters’. The clothings made of this fibre do not get wrinkled easily. It is always crisp and easily washable. PET is also derived from polyester which ip turn is used to make containers, utensils, films, wires etc.

(iv) Acrylic: Acrylic is just like wool and is used to make sweaters and suit lengths.

Question 3.
Describe the characteristic features of the synthetic fibres.
Answer:
Synthetic fibres are made from chemical substances. Their qualities are quite different from those of natural fibres. Following are the characteristic features of the synthetic fibres:
1. Raw material: All synthetic fibres are made from chemicals. They are prepared by a number of processes using raw materials of petroleum family called petrochemicals.

2. Strength: Synthetic fibres are quite strong. Nylon is the strongest known fibre.

3. Durability: Synthetic fibres are quite durable. They do not wither easily. They are so strong and durable that ropes and parachutes etc. are made by using synthetic fibres.

4. Soak less water: Synthetic fibres absorb small quantities of water and loose it quick, so they dry up very soon.

5. Availability and cost: Synthetic fibres are less expensive and readily available. That makes it a popular dress material.

Question 4.
What are plastics? How many types of plastics are available? Explain.
Answer:
Plastics are synthetic materials which can be moulded to give any desirable shape. Plastics are two types:
Thermoplastics: Those plasties which can be melted and reshaped again and again to give any shape on heating are called thermoplastics. Thermoplastics can be reused as many times as desirable e.g. PVC and polythene.

Thermosetting Plastics are those plastics which can be melted on heating mid cannot be reshaped again and again. Melamine, Bakelite etc. are examples of thermosetting plastics.

Question 5.
Write the characteristic features of plastics.
Answer:
Plastic is a wonder material. Following characteristic features make it a common and popular choice:
(i) Plastics are light in weight so they are easy to handle and manage.
(ii) Plastics are strong and durable so they are used to make buckets, mugs, ropes, etc.
(iii) Plastics are non-reactive as they do not get corroded when they come in contact with other materials or substances. This property make them perfect for storing food items and chemicals.
(iv) Plastics are poor conductors of electricity. They do not allow the electric current to pass through them easily. They are, therefore, used to make coverings of electric wires and other electric appliances.

Question 6.
Write advantages and disadvantages of synthetic fabrics.
Answer:
Following are the advantages of synthetic fabrics:
(a) Most of the synthetic fibres are wrinkle resistant. They do not get wrinkled easily. They easily retain their original shape, if they get wrinkled. So it is convenient to wash and wear.
(b) Synthetic fibres are strong so they can take up heavy loads easily. They have got high tensile strength, which enables them to carry weights.
(e) They have great elasticity. They can be easily streched.
(d) Synthetic fibres are generally soft, so they are used to make variety of clothes and clothing materials.

Disadvantages:
(a) Synthetic fibres cannot absorb moisture. This makes them unsuitable to be warm during summers. When our body sweatsv This make body sticky and irritates the skin
(b) They are dangerous to be worn near fire or heat, as they easily catch fire and is unfit to he worn.
(c) They cannot be easily ironed as they melt very easily.

Question 7.
How disposal of plastic is a problem? Explain.
Answer:
Plastic is wonderful synthetic material which is very useful. But biggest disadvantage of plastic is its disposal. Plastic is a non- biodegradable subtance, which do not get decomposed on its own by other microorganisms. So, accumulation of plastic is causing great danger for environment in the following ways:
(i) We throw plastics openly on roadsides and streets. This provide home to many disease causing germs.
(ii) Plastics if burned in the soil create more problem. They cannot be decomposed and prevents the water from seeping into the soil. This affects the plants adversLy. Water gets accumulated on the soil and cause muddy pubbles.
(iii) Buring the plasties produce toxic gases alongwith smoke which cause air pollution. Such an air is unfit for consumption and give birth to many respiratory problems in animals.
(iv) Plastic waste when dumped in water, cause water pollution. Aquatic animals consume these toxic plastics and die. It can also cause reproductive problems in aquotic animals.

Synthetic Fibres and Plastics Class 8 HBSE Notes

1. All the clothes we wear are made up of fabrics. Fabrics in turn are made up of fibres. Fibres can be of two types: natural fibre and manmade or synthetic fibres.
2. Natural fibres are those fibres which we get from plants and animals e.g. cotton, wool, silk, jute, etc.
3. Artificial or synthetic fibres are made up of the chemical substances by processing in factories and mills.
4. A synthetic fibre is chain of small units, woven together to form a long chain. These chemical substances or this chain of small units is called a polymer. All synthetic fhbrics are made up of these repeating units called polymers.
5. Rayon, Nylon, polyester etc. are examples of the manmade fibres.
6. These synthetic fibres are used for many other purposes, except making clothes. Nylon is a very strong fibre. It is used to make parachutes, socks, ropes, toothbrushes, sleeping bags and other drappery accessories.
7. Synthetic fibres are stronger than natural fibres. They absorb lesser amount of water than, the natural fibres. That is why raincoats etc. are made up of the synthetic fibres. They get dry! very soon and need less care and maintenance.
8. Plastics are synthetic materials which are used for many purposes. We can see objects made up of plastics all around us.
9. Plastics are also made up of polymers. Plastics can be moulded, melted and recycled. But all plastics are hot same.
10. Plastics are of two types: Plastics which can be melted, reshaped, bent easily are known as thermoplastics. The plastics which cannot be melted or reshaped are called thermosetting plastics.
11. Thermoplastics are used to make toys, combs, containers, etc. P.V.C. is an example of thermoplastic.
12. Thermosetting plastics are poor conductors of heat and are resistant to electricity. So they are used to make handles of utensils, electric plugs and switches, etc.
13. Plastics are very useful for us in every sphere of life. But they do have their disadvantages too.
Plastics are non-biodegrada,ble, so we cannot get rid of waste plastic easily. It is causing threat to our environment.
14. Environment friendly habbits like Reduce, Reuse, Recycle and Recovery of plastics can help in saving Environment.

Haryana State Board HBSE 8th Class Science Solutions Chapter 17 Stars and the Solar System Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 17 Stars and the Solar System

HBSE 8th Class Science Stars and the Solar System Textbook Questions and Answers

Question 1.
Which of the following is NOT a member of the solar system?
(a) An asteroid
(b) A satellite
(c) A constellation
(d) A comet
Answer:
(c) A constellation

Question 2.
Which of the following is NOT a planet of the sun?
(a) Sirius
(b) Mercury
(c) Saturn
(d) Earth
Answer:
(a) Sirius

Question 3.
Phases of the moon occur because:
(a) we can see only that part of the moon which reflects light towards us.
(b) our distance from the moon keeps changing.
(c) the shadow of the Earth covers only a part of the moon’s surface.
(d) the thickness of the moon’s atmosphere is not constant.
Answer:
(c) the shadow of the Earth covers only a part of the moon’s surface.

Question 4.
Fill in the blanks :
(a) The planet which is farthest from the Sun is __________.
(b) The planet which appears reddish in colour is __________.
(c) A group of stars that appear to form a pattern in the sky is known as a __________.
(d) A celestial body that revolves around a planet is known as __________.
(e) Shooting stars are actually not __________.
(f) Asteroids are found between the orbits of __________ and __________.
Answer:
(a) Neptune
(b) Mars
(c) constellation
(d) Satellite
(e) Meteors
(f) Mars and Jupiter.

Question 5.
Mark the following statements as true (T) or false (F) :
(а) Pole star is a member of the solar system. ( )
(b) Mercury is the smallest planet of the solar system ( )
(c) Uranus is the farthest planet in our solar system. ( )
(d) INSAT is an artificial satellite. ( )
(e) There are nine planets in our solar system. ( )
(f) Constellation Orion can be seen only with the telescope. ( )
Answer:
(a) False
(b) False
(c) False
(d) True
(c) False
(f) False

Question 6.
Match items in Column A with one or more items of Column B :

Answer:

Question 7.
In which part of the sky can you find Venus if it is visible as an evening star?
Answer:
In western sky.

Question 8.
Name the largest planet of the solar system.
Answer:
Jupiter.

Question 9.
What is a constellation? Name any two constellations.
Answer:
A group of stars in a recognizible shape is called a constillation. Orion and the Great Bear are constellations.

Question 10.
Draw sketches to show the relative positions of prominent stars in (i) Ursa Major and (ii) Orion.
Answer:

Question 11.
Name two objects other than planets which are members of the solar system.
Answer:
Meteors and Asteroids.

Question 12.
Explain how you can locate the Pole Star with the help of Ursa Major.
Answer:
Pole star is situated at the end of the Ursa Major. If a straight line starting from the last two stars is extended towards the north direction, it will lead to the Pole Star.

Question 13.
Do all the stars in the sky move? Explain.
Answer:
All the stars in the sky do not move, but they appear to move from east to west. This is actually due to rotation of earth on its axis. Earth moves from west to east. So it appears as the stars are rising from east and as the day dawns they sets in the west.

Question 14.
Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years away from the earth?
Answer:
Stars are away from the earth millions of kilometres away. It is not convenient to express such a large distance in the units of km. So the distance of stars from the earth is expressed in time taken by light to travel in one year. Eight light years mean time taken by light to travel in eight years.

Question 15.
Boojho made the following sketch (figure) of the solar system. Is the sketch correct? If not, correct it.
Answer:
No, the sketch is incorrect. The following sketch is correct.

Extended Learning – Activities and Projects

Question 1.
If possible, visit a planetarium. There are planetariums in many cities. In a planetarium you can see the motion of the stars, constellations and planets on a large dome.
Answer:
For self attempt.

Question 2.
On a moonless night observe the sky for a few hours. Look out for a meteor, which appears as a streak of light. September-November is a good time for observing meteors.
Answer:
For self attempt.

Question 3.
Learn to identify the planets visible to the naked eye and some prominent constellations such as Great Bear (Saptarshi) and Orion. Also try to locate the Pole Star and the star Sirius.
Answer:
For self attempt.

Question 4.
Select a convenient place on the roof of your house or in some playground from where you can watch sunrise clearly. Remember that you will have to do this activity for a few months. So, choose the place carefully. On a sheet of chart paper draw the outline of the eastern horizon indicating big trees, poles, etc. Mark the outline of the sheet so that you can place it in the same position every time. After every two weeks, note the position from where the Sun rises and mark this on your chart paper (Fig.). Also note the date of your observation. Repeat this for a few months. It is advisable that you start observations in the month of November or May.

Does the Sun always rise from the same direction? Discuss your observations with you teacher, parents and elderly people in your family or in the neighbourhood.
Answer:
For self attempt.

Question 5.
Form a group of studens. Prepare a model of the solar system showing the planets, and their relative sizes. For this take a large chart paper. Make spheres representing different planets according in their relative size (Use Table). You may use newspaper, clay or plasticine to make spheres. You can cover these spheres with paper of different colours. Exhibit your model in the class.

Answer:
For self attempt.

Question 6.
Try to make a scale model of the solar system showing distances of the planets from the Sun (Use Table 17.1). Did you face any difficulty? Explain it.
Answer:
For self attempt.

Question 7.
Solve the following riddle and try to make similar riddles yourself:
My first is in VAN but not in PAN
My second is in EARTH and also in HEAVEN
My third is in ONE and not in TWO
My fourth is in BUN and also in FUN
My last is in STAR but not in RADAR
I am a planet that moves round the Sun.
You can read more on the following websites:
→ http://www.nineplanets.org
→ http://www.kidsastronomy.com
→ http://www.solarsystem.nasa.gov/planets
→ http://aa.usno.navy.mil/fazz/does/moon- phases.html
Answer:
For self attempt.

HBSE 7th Class Science Stars and the Solar System Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Name any three celestial bodies.
Answer:
Stars, Satellite, Planets.

Question 2.
Name the planets of solar system which cannot be seen by naked eye?
Answer:
Neptune and Pluto.

Question 3.
Name the force which makes planets move around the sun.
Answer:
Gravitational force.

Question 4.
Which has higher density : Earth or Sun?
Answer:
Earth.

Question 5.
Name the planet narest to earth.
Answer:
Mars is nearest to earth.

Question 6.
Write the names of any two constellation.
Answer:
Great Bear and Orion.

Question 7.
A group of stars visible in winter season look like a cluster of twinkling gems.
Answer:
Pleiades constellation.

Question 8.
In which season of the year are the constellations scorpio and orion visible in the Northern Hemisphere?
Answer:
Orion – Winters.
Scorpio – Summers.

Question 9.
Define star.
Answer:
Stars are the heavenly bodies that are extremely hot and have light of their own.

Question 10.
Name the star which is nearest to the earth.
Answer:
Alpha Centuari.

Question 11.
Write the names of two planets which are closer to the sun than the earth.
Answer:
Mercury and Venus.

Question 12.
Name the planet nearst to the sun.
Answer:
Mercury.

Question 13.
Name the planet farthest from the sun.
Answer:
Neptune.

Question 14.
Which planet of the solar system is the hotest?
Answer:
Mercury.

Question 15.
Name the planet of the solar system Which is nearer to the Sun and Venus.
Answer:
Mercury.

Question 16.
Which planet in the solar system is nearest to the earth?
Answer:
Venus.

Question 17.
Name the planet, where there is no carbon dioxide.
Answer:
Mercury.

Question 18.
Name the planets, which has no moon?
Answer:
Mercury and Venus.

Question 19.
Give any two applications of remote sensing.
Answer:
(i) Preparing waste land maps.
(ii) Survey for ground water and mineral resources.

Question 20.
A constellation having seven prominent stars, is visible during the winter. Name the constellation.
Answer:
Orion.

Question 21.
A belt of assorted debris, which failed to assemble into a planet, is located between the orbits of two planets in the solar system. Name these two planets.
Answer:
Mars and Jupiter.

Question 22.
Which planet has rings around it?
Answer:
Saturn.

Question 23.
Name largest asteroid.
Answer:
Ceres.

Question 24.
Why do meteors shine?
Answer:
On entering earth’s atmosphere, meteors become hot and bum due to friction of earths atmosphere and start to shine.

Question 25.
What are meteorites?
Answer:
Big pieces of rock material which do not bum completely in atmosphere of earth, fall on its surface. These are called meteorites.

Question 26.
How are comets formed?
Answer:
When the path of objects near the edge of solar system is disturbed to push them near to sun, comets are formed.

Question 27.
After how much time Halley’s comet is seen?
Answer:
After every 76 years.

Question 28.
Why does pole star appear to be stationary?
Answer:
Pole star lies on the axis of rotation of earth and appears stationary when viewed from any part of earth.

Question 29.
What does the colour of a star signify?
Answer:
Colour of a star signifies its temperature.

Question 30.
Define a satellite.
Answer:
A satellite is a solid heavenly small sized body revolving round a planet.

Short Answer Type Questions

Question 1.
Distinguish between stars and planets.
Answer:

Question 2.
Explain the importance of stars for the people in ancient times.
Answer:
In ancient times when there were no compass, night sky was very useful in finding the direction. As pole star remains fix in the sky in north, it indicated north direction. As the stars change their position with time, it has been possible to find the time with relative position of stars.

Question 3.
How is the pole star located in the sky? Why is it so special?
Answer:
The earth rotates on its axis from west to east, therefore, the stars appear to move in opposite direction, i.e. east to west. But pole star lies on the axis of rotation of earth which is fixed, Therefore, pole star also seems to be fixed in the sky. It is always in north direction and is very useful for finding direction.

Question 4.
Distinguish between star and shooting star.
Answer:

Question 5.
What is a meteor? Why does it last for a very short time?
Answer:
Meteors are the heavenly bodies made of rocky material which enter earth’s atmosphere. When they travel through air they become hot and burn because of friction. Due to this, these rocky pieces melt and vaporises very fast and do not last long.

Question 6.
Distinguish between natural and artificial satellites.
Answer:
Natural satellites are far away from planets. They are comparatively larger in size and are present naturally. Artificial satellites are sent from earth with specific requirements. Their distanc, size and mass are lesser than the natural satellite.

Question 7.
What is solar system? Name the planets situated between the sun and the earth?
Answer:
The solar system consists of the sun, eight planets; and their satellites and other heavenly bodies like meteors, comets and asteroids. The sun is the centre of the solar system and all the planets revolve around the sun in elliptical paths called orbits. The planets situated between the sun and the earth are Mercury and Venus.

Question 8.
What are the phases of the Moon?
Answer:
Moon has no light of its own. It reflects light of the Sun falling on it. On new moon day, moon is between the sun and the earth and no reflected light from it reaches the earth. We cannot see moon on that day. The visible moon increases every day till fifteenth day from the new moon day, the full phase of the moon is visible.

Positions of the Moon in its orbit and its corresponding phases
So, the waxing and waning of moon periodically as it revolves around the earth is called phases of moon.

Question 9.
Why moon cannot be used as a communication satellite?
Answer:
Moon is a natural satellite of the earth but it cannot be used as a communication satellite because :

• It is very far away from earth.
• Its time period 27.3 days is too large.
• It has neither equitorial orbit nor polar orbit which makes a satellite useful for different purposes.

Question 10.
What are constellations? Name some easily recognizible constellations in the sky.
Answer:
Group of stars forming a recognizible shape is called a constellation. These group of stars are identified in different shapes. Constellations do not change their shape. They also appear to move from east to west as other stars appear to. Some major constellations are Ursa Major, Ursa Minor, Orion, Cassiopeia etc. Some of them are visible during summers while some are visible during winters.

Question 11.
What are various types of motions associated with the planet earth?
Answer:
The earth has four types of motion. These are :

(i) The earth’s daily rotation on its axis.
(ii) The earth’s annual revolution around the sun.
(iii) The earth’s precession (conical motion of earth’s axis).
(iv) As a part of solar system, the earth’s motion in space along with the sun.

Question 12.
Explain the constellation Ursa Major.
Answer:
Ursa Major is one of the most famous constellation. We can see this constellation during summers. It is also called the Great Bear or the Saptarishi. There are seven prominently shining stars in this constellation which are arranged in shape of a question mark. At the tail of this constellation lies the Pole Star.

Question 13.
Describe the constellation also called the hunt.
Answer:
A well known constellation named Orion is also called the hunter. This constellation can be seen in the late evenings of winter. It has seven or eight brightly shining stars arranged in shape recognized with hunter. The brightest star in the sky Sirius is located at the extended line from the tail of this constellation.

Question 14.
What are asteroids?
Answer:
Asteroids are the small objects which revolve around the sun in a large gap between the orbits of Mars and Jupiter. These are quite large in their number and are considered as the part of our solar system. Each asteroid has its own orbit.

Question 15.
What are comets?
Answer:
Comets are the part of our solar system which revolve around the sun in highly elliptical orbits. It appears with a bright head and a long tail. The length of the tail grows in size as it approaches the sun. The tail is always directed away from sun.

Question 16.
What are various superstitions connected with appearance of comets?
Answer:
They are considered to be the messangers of destruction and disasters. They are supposed to bring wars,epidemics and flood with them. So, their appearance is considered as unauspicious.

Question 17.
List five uses of artificial satellites.
Answer:

• Weather forecasting.
• Radio and television transmission.
• Long distance communication.
• Locating mineral resources.
• Gathering information about our space.

Long Answer Type Questions

Question 1.
Explain celestial sphere.
Answer:
The large imaginary sphere on which all the heavenly bodies like stars, planets and satellites seems to lie is known as celestial sphere. Since we are on the earth, the earth appears stationary to us. When we look at the sky, the various objects in the sky like the stars and the moon appear to be moving round the earth. In other words, the celestial sphere appears to be moving from east to west round the earth. This apparent motion of the celestial sphere from east to west is actually due to the daily rotation of the earth from west to east. Since the earth rotates from west to east, the celestial sphere appears to rotate in the opposite direction, from east to west.

Question 2.
What are constellations? Explain. Name some prominent constellations with their Indian names.
Answer:
The groups of stars which seem to be arranged in the sky in beautiful patterns and recogniseable shapes are known as constellations. With each constellation, the ancient astronomers assigned the name of an object which it appears to resemble. There are 88 constellations into which the whole of the sky has been divided. In Indian astronomy, the constellations are known as Nakshatras.

Some prominent constellations with their Indian names are given below :
(i) Ursa Major or Saptarishi.
(ii) Ursa Minor or Laghu Saptarishi
(iii) Orion or Mriga or Vyadha
(iv) Tarus or Vrashba
(v) Scorpio or Vrishchika.

Question 3.
What is pole star? What is specific j about its position in the sky?
Answer:
There is only one star in the sky which appears stationary to an observer on earth. This star is named as pole star (Polaris) or Dhruvtara in India. This star appears stationary because, i it lies in the direction of the axis of the Earth about which the earth rotates. Any point on or j along the axis of a rotating body appears to be stationary. So, the pole star that lies along the direction of the axis of rotation of the earth, always sppears to be stationary.

Question 4.
What are artificial satellites? Explain their usage.
Answer:
Man made objects orbitting in outer space around the earth or any other planet are called artificial satellites of earth or that particular planet. The satellite like INSAT 3E or Kalpana Chawla I are examples of artificial satellites. Artificial satellites have many practical applications that effect our lives in many ways, i Long distance transmission of television programmes, communication through telephones and internet could be possible because of them. Artificial satellites are also used for research, defence and remote sensing. Remote sensing means collecting information from a distance. Information is collected regarding weather, agriculture, land and ocean features including movement of fish.

 Stars and the Solar System Class 8 HBSE Notes

• We can see many celestial bodies in a clear night sky.
• Stars are one of the celestial bodies which emit light of their own.
• Sun is also one of the stars which emits light and is a great source of heat. It is the closest star which is the centre of our solar system.
• Stars are many light years away from the earth and thus look very small from earth.
• Stars appear to travel from east to west.
• Pole star is the most shining star in the night sky. The pole star appears to.be stationary. It is situated near axis of rotation of earth and is thus helpful in finding direction.
• A group of stars, appearing in different shapes are called constellations. Their shapes resemble different objects and thus are named after the names of the objects.
• Other improtant parts of night sky are the planets. Planets are those celestial bodies, which revolve around sun.
• Our solar system consists of eight planets revolving around sun. It also consists of many other celestial bodies like asteroids, comets and meteors.
• Comets are the celestial bodies that revolve in highly elliptical orbits around sun.
• Bright streak of light in a night sky are commonly called shooting stars or meteors.
• A celestial body revolving around another celestial body is called a satellite.
• Artificially sent bodies in space, which revolve around earth or any other planet or a natural satellite is called an artificial satellite
• Jupiter is the largest planet while Venus is brightest planet in the night sky.
• Moon is the natural satellite of the earth. Moon appears in different phases. The phases of Moon occur because we can see only that part of the moon which reflects light towards us.

Haryana State Board HBSE 8th Class Science Solutions Chapter 2 Micro Orgmisms: Friends and Foe Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 2 Micro Orgmisms: Friends and Foe

HBSE 8th Class Science Micro Orgmisms: Friends and Foe Textbook Questions and Answers

Question 1.
Fill in the blanks:
(a) Microorganisms can be seen with the help of a ……….. .
(b) Blue green algae fix ………….. directly from air to enhance fertility of soil.
(c) Alcohol is produced with the help of ………….. .
(d) Cholera is caused by ……………… .
Answer:
(a) microscope
(b) atmospheric nitrogen
(c) yeast
(d) bacteria.

Question 2.
Tick the correct answer:
(a) Yeast is used in the production of:
(i) sugar
(ii) alcohol
(iii) hydrochloric acid
(iv) oxygen
Answer:
(ii) alcohol

(b) The following is an antibiotic:
(i) Sodium bicarbonate
(ii) Streptomycin
(iii) Alcohol
(iv) Yeast
Answer:
(ii) Streptomycin

(c) Carrier of malaria-causiiig protozoan is:
(i) female Anopheles mosquito
(ii) cockroach
(iii) housefly
(iv) butterfly
Answer:
(i) female Anopheles mosquito

(d) The most common carrier of communicable diseases is:
(i) ant
(ii) housefly
(iii) dragonfly
(iv) spider
Answer:
(ii) housefly

(e) The bread or idli dough rises because of:
(i) heat
(ii) grinding
(iii) growth of yeast cells
(iv) kneading
Answer:
(iii) growth of yeast cells

(f) The process of conversion of sugar into alcohol is called:
(i) nitrogen fixation
(ii) moulding
(iii) fermentation
(iv) infection
Answer:
(iii) fermentation

Question 3.
Match the organisms in Column I with their action in Column II.

Answer:

Question 4.
Can microorganisms be seen with the naked eye? If not, how can they be seen?
Answer:
Some organisms are very small in size. They are so small that they cannot be seen with naked eyes. A microscope has to be used to see these organisms. Therefore, they are called microorganisms.

Question 5.
What are the major groups of microorganisms?
Answer:
Microorganisms can mainly be divided into five groups:
(i) Bacteria
(ii) fungi
(iii) protozoa
(iv) algae,
(v) virus.

Question 6.
Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer:
Bacteria like Rhizobium, Azotobacter, Blue green algae like Anabaena and Nostoc can fix atmospheric nitrogen in soil.

Question 7.
Write 10 lines on the usefulness of microorganisms in our lives.
Answer:
Microorganisms are very useful to us.
They help us in following ways:
(i) Microorganisms help us in food sector. They are used for curdling of milk, preparation of bread, cake, etc.
(ii) Microorganisms are used to produce alcohol at large scale.
(iii) They are also used to produce wine.
(iv) Yeast is used to prepare vinegar.
(v) They are also used as preservatives for food items.
(vi) Used to make different medicines, especially the antibiotics.
(vii) Microorganisms are used to prepare vaccines for various disease.
(viii) Useful for agriculture sector, as they enhance the fertility of soil by fixing the biological nitrogen.
(ix) They work as natural cleansers, as they decompose the dead bodies of plants and animals.
(x) Microorganisms prepare manures by decomposing dead bodies of plants and animals.

Question 8.
Write a short paragraph on the harms caused by microorganisms.
Answer:
Microorganisms can prove very harmful to us, as they cause a number of human and animal diseases. Diseases in humans like common cold, tuberculosis, measles, chiken pox, Polio, Cholera, Typhoid, Hepatitis B, Malaria, etc. are caused by microorganisms. Some serious deseases like Anthrax is also caused in animals by the microbes. Microbes grow on food products and render them unfit for consumption.

Consumption of such food causes food poisoning. Microbes also spoil clothings and leather products. Microbes also cause diseases of plants like blights in potatoes, sugarcanes, oranges etc. They also reduce the yield.

Question 9.
What are antibiotics? What precautions must be taken while taking antibiotics?
Answer:
Medicines taken to kill or stop the growth of harmful or disease causing microbes in human body are called antibiotics. Antibiotics are very useful as only antibiotics can save us from many microbial infections and diseases. Antibiotics are made from fungi and bacteria. Alexander Fleming discovered the first antibiotic called Penicillin in 1929. Now-a-days a number of antibiotics are used to cure a variety of human and animal diseases. Streptomycin, Tetracycline, Erythromycin etc. are some commonly used antibiotics.

Antibiotics should only be taken when adviced by a qualified physician. Antibiotics should only be taken when needed otherwise, they become less effective for future use.

Extended Learning – Activities And Projects

1. Pull out a gram or bean plant from the field. Observe its roots. You will find round structures called root nodules on the roots. Draw a diagram of the root and show the root nodules.
Answer:
Do it yourself.

2. Collect the labels from the bottles of jams and jellies. Write down the list of contents printed on the labels.
Answer:
Ingredients: Sugar, Mixed fruit pulp, Gelling Agent (E440), And acidity regulator (E330). Permitted synthetic food colour (E122) and added artificial flavours. Contains permitted class-II Preservatives (E211, E224).

3. Visit a doctor. Find out why antibiotics should not be overused. Preapare a short report.
Answer:
Antibiotics should not be overused because they reduce of power of immunity.
(i) Regular or frequent use make the drug ineffective when needed in future.
(ii) They kill beneficial bacteria in our body.
So, antibiotics should only be consumed when prescribed by doctore only.

4. Project:
Requirement – 2 text tubes, marker pen, sugar, yeast powder, 2 ballons and lime water.

Take two test tubes and mark them A and B. Champ these tubes in a stand and fill them with water leaving some space at the top. Put two spoonfuls of sugar in each of the test tubes. Add a spoonful of yeast to test tube B. Inflate the two balloons incompletely Now tie the balloons on the mouths of each test tube. Keep them in a warm place, away from sunlight. Watch the setup every day for next 3-4 days. Record you observations and think of an explanation.

Now take another test tube filled V4 with lime water. Remove the balloon from test tube B in such a manner that gas inside the balloon does not escape. Fill the balloon on the test tube and shake well. Observe and explain.
Answer:
The balloon in test tube B will get inflated because process of fermentation has taken place in test tube B due to yeast bacteria and carbondioxide gas produce during this process has inflated the balloon. Now the balloon will get a little deflated as gas in consumed by the lime water and the lime water will turn milky.

5. For more information, visit the following websites.

• www.microorgan.isms
• www.biology4kids.com/files/micro_main html

HBSE 8th Class Science Microorganisms: Friend and Foe Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Define microorganisms.
Answer:
Very small organisms around us which cannot be seen with naked eyes are called microorganisms.

Question 2.
Where are microorganisms found?
Answer:
Microorganisms are found everywhere. In air, water and in the body of other organisms.

Question 3.
Name the groups in which microorganisms can be divided.
Answer:
Bacteria, fungi, protozoa, some algae and viruses.

Question 4.
Which common diseases do viruses cause?
Answer:
Viruses cause diseases like common cold, flu and most of the coughs.

Question 5.
Which serious diseases are caused by viruses?
Answer:
Diseases like polio and chicken pox.

Question 6.
Name diseases caused by protozoans.
Answer:
Dysentery and malaria are caused by protozoans.

Question 7.
Name any two algae.
Answer:
Chlamydomonas and spirogyra.

Question 8.
Name any two protozoa.
Answer:
Amoeba and paramecium.

Question 9.
Name any two fungi.
Answer:
Rhizopus and Aspergillus.

Question 10.
Name unicellular microbes.
Answer:
Bacteria and protozoa.

Question 11.
Name multicellular microbes.
Answer:
Algae and fungi.

Question 12.
Which bacteria is responsible for the curdling of milk?
Answer:
Lactobacillus.

Question 13.
Which bacteria is used to produce alcohol?
Answer:
Yeast.

Question 14.
What do you mean by fermentation?
Answer:
Conversion of sugar into alcohol using yeast is palled fermentation.

Question 15.
Who discovered the process of fermentation?
Answer:
Louis Pasteur.

Question 16.
What are antibiotics?
Answer:
Medicines used to kill or stop the growth of diseases causing microorganisms inside human body are called antibiotics.

Question 17.
Who discovered the first antibiotic?
Answer:
Alexander Fleming.

Question 18.
Which antibiotic did Alexander Fleming discover?
Answer:
Penicillin.

Question 19.
Which microorganism is not affected by antibiotics?
Answer:
Viruses.

Question 20.
Name certain diseases which can be prevented by vaccination.
Answer:
Cholera, tuberculosis, small pox, hepatitis, polio, etc.

Question 21.
Name microorganisms which can fix atmospheric nitrogen.
Answer:
Bacteria and blue green algae.

Question 22.
Name one free living bacteria and one blue green algae who fix nitrogen using oxygen from atmosphere.
Answer:
Azotobacter, Anabaena.

Question 23.
What are pathogens?
Answer:
Disease causing microorganisms are called pathogens.

Question 24.
What are communicable diseases?
Answer:
Diseases which spread with physical contacts are called communicable diseases.

Question 25.
Name an insect which is a common carrier of microbial diseases.
Answer:
Housefly.

Question 26.
Name the carrier of dengue virus.
Answer:
Female Aedes mosquito.

Question 27.
Where do mosquitoes breed?
Answer:
Mosquitoes breed in stagnant water and damp places.

Short Answer Type Questions

Question 1.
What are the major group of the microorganisms?
Answer:
Major groups of microorganisms are:
(i) Bacteria: They are non-green single celled microorganisms.
(ii) Fungi: They are long thread like unicellular as well as multicellular microorganisms.
(iii) Algae: Aquatic* photosynthetic organisms commonly called sea weeds.
(iv) Protozoan: They are unicellular organisms.
(v) Virus: They are non-cellular microbes which only get active inside a living cell.

Question 2.
Describe various types of bacteria with examples.
Answer:
On the basis of their shape, the bacteria are divided into three types:
(i) Bacillus or rod shaped: Long rod shaped bacteria like Bacillus, Pseudomonas, Lactobacillus.
(ii) Cocus or round shaped: Streptococus, Sarcinaltc. are round shaped bacteria.
(iii) Spirillum or spiral: Comma shaped bacteria, they can also be spiral rods e.g. Camphilovector, Triponema.

Question 3.
State some beneficial effects of bacteria.
Answer:
Bacteria are very useful to us. Some of the beneficial effects of bacteria are as follows:
(i) Bacteria is helpful in agriculture as it fixes the atmospheric nitrogen in soil.
(ii) Products like vinegar, alcohol, curd etc. are obtained.
(iii) It decomposes the dead bodies of plants and animals.
(iv) Valuable medicines like antibiotics are obtained by bacteria.

Question 4.
Mention important uses of fungi,
Answer:
(i) Some fungi are eaten raw as food such as mushrooms.
(ii) Yeast being rich in amino acids and proteins are an important source of food for man and his farm animals.
(iii) Yeast is also used in the preparation of products like wine and bears from fruit juices or barley. It brings about fermentation of sugars into alcohols and carbondioxide.

Question 5.
Write the harmful effects of Bacteria.
Answer:
Bacteria cause a number of diseases in humans and animals. Diseases like cholera, pneumonia, tuberculosis are caused by bacteria. It also causes food poisoning as it makes the food unfit to consume. It spoils leather and clothings.

Question 6.
Write the harmful effects of fungi and algae.
Answer:
Some fungi causes damages or diseases. Smuts and rusts are fungi that damage the crops. Ring-warm and atheletes food diseases are caused by fungi. Amanite mushrooms contain poisonous substance. Algae are great nuisance as they spoil the drinking water. Excess growth of algae also blocks the movement of water in channels.

Question 7.
Write the diseases caused by protozoa.
Answer:
Several protozoa cause diseases in man and other animals. Antaemoeba Histolytica causes amoebic dysentry in man. Dangerous plasmodium causes malaria and dengue. Trypanosoma, causes sleeping sickness in man, cattle, pigs and horses.

Question 8.
Describe the main characteristics of viruses in brief.
Answer:
(i) They do not possess any cell wall or cell membrane.
(ii) They can only multiply in the bodies of living beings.
(iii) They cause many diseases.
(iv) Antibiotics do not have any affect on viruses.

Question 9.
What are vaccines?
Answer:
A vaccine consists of antigens of mild strains of pathogens of a particular disease. Vaccine when injected into the blood stream stimulates white blood cells to produce antibodies. These antibodies act against the antigens and neutralise their toxins or destroy them.

Question 10.
How does microorganisms enter into our body?
Answer:
Microorganisms enter into our body:
(i) through the air we breathe.
(ii) through the water we drink.
(iii) through direct contact with infected person.
(iv) by the use of polluted water or food.

Question 11.
What are viruses?
Answer:
Viruses are microscopic organisms. These are the smallest organisms. They may be rod-shaped, polygonal, spherical or even cubical. There are four types of viruses: Plant viruses, Insect viruses, Bacterial viruses and mammalian viruses.

Long Answer Type Questions

Question 1.
What do you understand by microorganisms? Describe their different forms.
Answer:
Different living organisms present around us which cannot be seen with naked eyes are called microorganisms. They are present in soil, water and air. Microorganisms can be divided into five groups:
(i) Bacteria are the non-green single celled microscopic organisms. They have a rigid cell wall. It has a nuclear material. They are the simple most common form of life on earth. They have different shapes and sizes.

(ii) Algae are aquatic, photosynthetic organisms. In simple terms they are called sea weeds. They range in size, colour. Algae are of green, blue, red and blue^green colours.

(iii) Fungi are plants not having chloroplast but a cell wall. They are both unicellular and multicellular. Moulds, mushrooms etc. are fungi.

(iv) Protozoa are one celled living things. They range from 2 to 200 microns. Amoeba, Paramecium, Euglena and Plasmodium etc. are protozoas.

(v) Viruses are the non-cellular microbes. They are smaller than bacteria and multiply only inside a living cell.

Question 2.
Write a short note on Bacteria.
Answer:Bacteria are non-green single celled microscopic organisms. They have a rigid cell wall. They have a nuclear material. They are simple most common form of life on earth. They occur singly but are seen in chain of cells. They are of different shapes such as rod shaped, spiral, cork screw and comma shaped.

Bacteria are harmful for us, but some bacteria are quite useful. The most disadvantageous aspect of bacteria is their disease causing tendency. Various serious diseases like Tuberculosis, cholera, typhoid etc. are caused by bacteria. Bacteria are useftd as they are used to prepare vaccines and antibiotics. They decompose waste material and fix the atmospheric nitrogen into soil to enhance its fertility. Bacteria are also used to manufacture vinegar, acetic-acid, curd and cheese etc.

Question 3.
What are fungi? How are they useful or harmful to us?
Answer:
Fungi are microorganisms which exist in unicellular as well as multicellular forms. Some of the fungus like mushroom, yeast etc. can be seen with naked eyes. They have long thread like structures called hyphae. Fungus can reproduce sexually as well as asexually. Fungi are both harmful and useful. Smuts, crusts and ringworm etc. cause many diseases in humans as well as in animals and plants.

They are useful as they are used as food in many parts of world. Mushrooms are the mostly used food around the word. Yeast is used to make alcohol, breads, bhathuras, idlis, dosas etc. Penicillium is used to make penicillin an antibiotics.

Question 4.
What do you know about Protozoa?
Answer:
Protozoa are single celled living things. The size ranges from 2 microns to 200 microns.

Amoeba, Paramesium, Euglena, Plasmodium etc. are examples of Protozoa. Protozoa are the part of animal kingdom because they do not have chlorophyll.

They are oval, elongated and spherical in shape. Protozoa cause diseases like malaria and dengue. Protozoa like Entamoeba Histolytica causes amoebic dysentery in man. Trypanosoma causes sleeping sickness in man and cattle. Protozoa are useful as they form an important link in acquatic food chain. They decompose organic matters to convert them in useful soil nutrients.

Question 5.
What are food preservatives? Explain some common preservatives.
Answer:
Chemicals used to check or stop the growth of harmful microorganisms in food are called preservatives. These preservatives keep the edibles protected from the invasion of microorganisms which can spoil the food.
Some commonly found preservatives are:
Salt: Common salt is used to preserve meat, fish, amla, raw mangoes, tamarind, etc.

Sugar preserves jam, jellies, squashes and other sweet drinks. Sugar reduces the moisture and checks the growth of microorganisms.

Oil: Edible oils are used as preservatives in vegetables and pickles. Oil does not allow the moisture to surface thus preventing the growth of harmful bacteria.

Vinegar preserves vegetables, fruits, fish, meat and pickles.
Other processes like pasteurization etc. also preserve the milk and other liquids.

Question 6.
How can we detect the spoilage in food?
Answer:
Following indications help us an detecting the spoilage in food:
(a) Odour:
When food gives out smell, it is the indication that the bacteria has spoiled the food. Food gives out repulsive smell when bacteria breaks the proteins found in food. This is called Putrefaction.

(b) Discoluration:
Growth of microbes on food results in discolouration of food black. Moulds on breads, blue green moulds on citrus fruits and cheese cause the change in the original colour of the food. Any small discolouration indicates that the food has been spoiled and is unfit for consumption.

(c) Souring:
Sometimes the cooked food starts tasting sour. It is due to the production of acids by the action of certain bacteria. Milk starts tasting sour if not preserved properly, same is the case with curries and gravies of some vegetables.

(d) Sliminess:
Sometimes the food became slimy. It is also due to action of certain bacteria thread like slimes are also caused due to moulds.

(e) Gas formation:
Due to action of bacteria gases like carbondioxide are produced. They also spoil the food by making it swell or become spongy.

Microorganisms: Friend and Foe Class 8 HBSE Notes

1. Many living organisms exist around us in water, soil and air. They are so small that they cannot be seen with naked eyes. These tiny organisms are called microorganisms or microbes.
2. Microorganism can live in any kind of extreme environment like hot, cold, humid, icecold, saline water, desert or hot soil.
3. Microorganisms have wide variety of structural forms. They can be from unicellular to multicellular organisms.
4. Microorganisms are classified as bacteria, fungi, protozoa, algae and viruses.
5. Viruses are different from other microorganisms, yet referred to as the microorganism.
6. These microorganisms are helpful economically. They are also used to make many medicines.
7. These microorganisms can be very harmful too as they cause many diseases. Such microbes are called pathogens.
8. Microorganisms are used to enhance the fertility of the soil as they trap the biological nitrogen and fix them in the soil, which in turn is used by plants.
9. Microorganisms work on the dead bodies of the plants and animals to decompose them. They, thus, work as the natural cleansers of the environment.
10. Some microorganisms destroy our food by growing on it. The food infected by these microorganisms become unfit to consume. If consumed it can cause food poisoning.
11. Some special microbes reside in the nodules of the leguminous plants which fix the biological nitrogen from air into soil. The nitrates and nitrites present in soil are further converted into nitrogen gas and released in atmosphere. This whole cycle is called the nitrogen cycle.

Haryana State Board HBSE 8th Class Science Solutions Chapter 1 Crop Production and Management Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 1 Crop Production and Management

HBSE 8th Class Science Crop Production and Management Textbook Questions and Answers

Question 1.
Select the correct word from the following list and fill in the blanks:
Float, water, crop, nutrients, preparation
(a) The same kind of plants grown and cultivated on a large scale at a place is called …………… .
(b) The first step before growing crops is …………… of the soil.
(c) Damaged seeds would …………… on top of the water.
(d) For growing of crop, sufficient sunlight and …………… and …………… from the soil are essential.
Answer:
(a) Crop
(b) preparation
(c) float
(d) water, nutrients.

Question 2.
Match items in column ‘A’ with those in column ‘B’:

Answer:

Question 3.
Give two examples of each:
(a) Kharif Crop
(b) Rabi Crop
Answer:
(a) Paddy and maize
(b) Wheat and gram

Question 4.
Write a paragraph in your own words on each of’the following:
(a) Preparation of soil (b) Sowing (c) Weeding (d) Threshing.
Answer:
(a) Preparation of Soil:
Soil is prepared to sow the seeds. It is tilled to loosen the soil particles for better absorption of water and manures. Loosening of soil particles add humus and nutrition to the soil for better crops. Tilling of soil is done by using ploughs which are pulled by bulls. Tractor driven cultivators are also used to till the soil.

(b) Sowing:
Sowing means implanting the seeds in the prepared soil. Seeds are first selected. Better and healthy breeds of seeds are selected. They are then sowed in the fields with the help of seed drills and funnel shaped tools. The funnel, has a long body on one end of which is placed in soil. Seeds are put in the funnel and seeds go into the soil through long pipe which is carried over in the field with help of ploughs, the lower end pierces through the soil, spreading the seeds. Some seeds are simply spread through the field by hand. Some saplings are planted directly in the field manually.

(c) Weeding:
Unwanted plants growing along the crop are called the weeds. These weeds absorb the nutrients from the soil which are ment for the crops. They are, therefore, removed from the fields. Weeds are either removed manually or by mechanical tools. Certain chemicals are also used to kill the unwanted plants growing in the crops.

(d) Threshing:
Separation of grains from the chaff is called threshing. Seeds are removed from the chaff by threshers. When the crop is harvested, it is cut alongwith the stalks. They are then separated and the grains are removed. This whole process takes place with the help of a huge machine called combine.

Question 5.
Explain how fertilisers are different from manure.
Answer:
Differences between fertilizers and manure:
(i) Fertilisers are chemical substances, while the manures are the organic substances.
(ii) Fertilisers are prepared in the factories while the manures are prepared in fields.
(iii) Fertilisers don’t provide any humus to soil while manures provide a lot of humus.
(iv) Fertilisers are rich in plant nutrients will manures are less rich in plant nutrients.

Question 6.
What is irrigation? Describe two methods of irrigation which conserve water.
Answer:
Watering the crops in the fields is called irrigation. Irrigation is done at different intervals. Irrigation should be done in a way in which water does not get wasted, two such methods which conserve water are:
(i) Sprinklers:
Sprinklers work like fountains. Long perpendicular pipes have holes at regular distances, when water is supplied, it comes out of these holes and spray water in field. These holes have rotating nozzles which sprinkle water in all directions. Limited outflow of water, controls wastage of water.

(ii) Drip System:
This system allows the water to flow drop by drop at the roots of the plants. It contains a main pipe which have further lateral pipes containing small nozzles for the outflow of the water. Nozzles are such placed that they throw water at the roots of the plants, which saves water from flowing around uselessly.

Question 7.
If wheat is sown in kharif season, what would happen? Discuss.
Answer:
If wheat are grown in Kharif season, they would not grow as they do not need ihuch water to grow. The seeds would get destroyed in excess water due to rainy season.

Question 8.
Explain how soil get affected by the continuous plantation of crops in a field.
Answer:
Continuous plantation of crops drains off the nutrients of the soil. It leaves the land unfertile and unable to bear crop. It does not give any time to the soil to replenish the absorbed nutrients by the crops, thus unable to sustain any further healthy and good crop.

Question 9.
What are weeds V How can we control them?
Answer:
Weeds are the unwanted plants growing along crops. They share the nutrients meant for plants and thus are harmful. We can control weeds with the help of chemicals called weedicides. Weeds are the unwanted plants growing along the main crops. They are either removed manually or by chemicals. Weedicides are sprayed in the fields to kill the unwanted plants. These weedicides do not affect the main crop. Weeds are removed or killed during their vegetative phase before flowering or bearing seeds.

Question 10.
Arrange the following boxes in proper order to make a flow chart of sugarcane crop production:

Answer:

Question 11.
Complete the following word puzzle with the help of clues given below:

Down
1. Providing water to the crops.
2. Crop grains have to be kept for a long time in proper conditions.
5. Certain plants of the same kind grown on a large scale.

Across
3. A machine used for cutting the taatured crops.
4. A rabi crop that is also one of the pulses.
6. A process of separating the grain from chaff.
Answer:

Activity 1.3

Extended Learning – Activity And Projects

Question 1.
Sow some seeds in the soil and arrange to water them by drip irrigation. Observe daily.
(i) Do you think it can save water?
(ii) Note the changes in the seed.
Answer:
(i) Yes, drip irrigation saves water as it doe not allow the water to flow on sides and get wasted.
(ii) Seeds slowly get germinated.

Question 2.
Collect different types of seeds and put them in small bags. Attach these bags in a herbarium file and label them.
Answer:
Do it yourself.

Question 3.
Collect new agricultural machine pictures and paste in a file with their names and uses.
Answer:
Tractor to drew ploughs and carriage combines for threshing.
Plough for tilling soil.
Winnowing machine for removing chaff.

4. Project Work: Visit a farm, nursery or a garden nearby. Gather information about:
(i) importance of seed selection
(ii) method of irrigation
(iii) effect of extreme cold and extreme hot wather on the plants
(iv) effect of continuous rain on the plants
(v) fertilisers / manure used.
Answer:
(i) Good seed give good crops.
(ii) Traditional and modern
(a) Traditional: Moat, Chain pumps, Dhekli and Rahat
(b) Modern: Drip irrigation and Sprinklers.
(iii) Extreme cold and heat destroy the crops.

(iv) → Continuous rain get plants decomposedand waer logged in fields.
→ Minerals and fertilisers get flown away.
→ Top fertile layers get destroyed.
(v) Enhance the productivity of soil.

For more information, visit:

• www.krishiworld.com / html / balanced fertiliser.htm.
• www.ikis.com / links / ap.cultivation.html.

HBSE 8th Class Science Crop Production and Management Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Why do every living organism need food?
Answer:
Every living organism needs food to grow and perform various other activities and body functions.

Question 2.
Where do we get our food from?
Answer:
We get our food from plants and animals.

Question 3.
What is agriculture?
Answer:
Growing and managing crops is called agriculture.

Question 4.
What is crop?
Answer:
When same type of plants are grown at a large scale, it is called crop.

Question 5.
Name the factors controlling crop production.
Answer:
Soil, water, sunlight and air.

Question 6.
What are the rainy season crops called?
Answer:
Kharif crops.

Question 7.
What are the summer season crops called?
Answer:
Zayed crops.

Question 8.
What are the winter season crops called?
Answer:
Rabi crops.

Question 9.
Name any three Kharif crops.
Answer:
Paddy, maize, cotton.

Question 10.
Name any three Rabi crops.
Answer:
Wheat, gram, mustard.

Question 11.
Name any three Zayed crops.
Answer:
Moong, musk melon, bitter gourd.

Question 12.
What is tilling?
Answer:
Tilling is the loosening and turning of the soil.

Question 13.
What are crumbs?
Answer:
Crumbs are big pieces of soil present in fields, which require tilling.

Question 14.
Which agricultural tools are Used for tilling?
Answer:
Plough, hoe and cultivators.

Question 15.
Name tools used for sowing.
Answer:
Funnel shaped pipe with plough and seed drill.

Q. 16.
What is transplantation of seeds?
Answer:
Small saplings of plants are directly plantedj in fields. This is called transplantation.

Question 17.
What are fertilizers and manures?
Answer:
Manures and fertilizers are the substances added to soil to enhance its fertility and nutrients.

Question 18.
Which manure is called organic manure?
Answer:
Manure obtained from the dead bodies of plants and animals.

Question 19.
Name any two important fertilizers.
Answer:
Urea, NPK (Nitrogen, Phosphorus, Potassium).

Question 20.
What is a fallow?
Answer:
An uncultivated field between two croppings is called a fallow.

Question 21.
Write sources of irrigation.
Answer:
Wells, tubewells, ponds, lakes, rivers, dams and canals.

Question 22.
What is harvesting?
Answer:
Cutting of the crop after it is mature is called harvesting.

Question 23.
What is threshing?
Answer:
Separating seeds from the chaff is called threshing.

Short Answer Type Questions

Question 1.
What do you mean by agriculture?
Answer:
The term agriculture is derived from the Latin words ‘Ager’ which means field and ‘culture’ which means cultivation. Thus, cultivation in fields means agriculture.

Question 2.
Write the names of various agricultural practices undertaken to produce a crop.
Answer:
Following agricultural practices are performed to produce the crop:
1. Soil preparation
2. Sowing
3. Adding manure and fertilizers
4. Irrigation
5. Protection from weeds
6. Harvesting
7. Storage.

Question 3.
How many categories of crops are sown in India based on the seasons?
Answer:
Three categories of crops are sown in India based on the seasons:
(i) Kharif crops are sown during rains.
(ii) Rabi crops are sown during winters, and
(iii) Zayed crops are grown during summers.

Question 4.
Why is the $oil turned and loosened before seeds are sown?
Answer:
The soil is turned and loosened during the process of ploughing. The ploughing loosens the soil particles and turn the soil of upper

surface. This allows the nutrients from the dead organism to be released back in the soil and better penetration and absorption of nutrients by plant roots.

Question 5.
What are manures and fertilizers?
Answer:
Manures and fertilizers are used to enhance the productivity and fertility of the field. Manure is made of waste products of animals and plants. Fertilizers are chemicals rich in nitrogen, potassium.

Question 6.
What is the role of water in production of crops?
Answer:
Water is essential for all plants. Crops should get enough water at different stages of their growth. Different crops require different amount of water in the field. The wheat crop requires moderate amount of water at the time of sowing, flowering and ripening of crop.
Therefore, corps should be irrigated properly according to their needs.

Question 7.
What are the different methods of irrigation?
Answer:
Different methods of irrigation are adopted according to the requirement of soil and size of the field. Some common methods of water supply are through small channels, which get water from tubewells and canals, lift irrigation, sprinkler, dripping irrigation, etc.

Question 8.
Define weeding. What tools are used for weeding?
Answer:
Weeds are unwanted and undesirable plants which grow alongwith the crop plants in the field. They grow rapidly than the crop plants and cause harm to them. It is, therefore, essential to remove weeds at proper time. The process of removing the weed plants is called weeding. It is done either by hand or by khurpi. It is also done by spraying chemicals or weedicides.

Question 9.
What is humus? How is it formed?
Answer:
Humus is a kind of soil rich in nutrients. It is formed by the microbial action on dead decaying bodies and leaves. It is generally formed on those spots where-there are dense layers of trees. The soil below it becomes dark having more number of pathogenic bacteria.

Question 10.
What are pesticides?
Answer:
The chemicals which are used to protect crops from the organisms called pests are known as pesticides. They are used to kill eggs and larvae of insects who could cause harm to the crops. Pesticides are sprayed in the fields by different methods at different intervals.

Question 11.
What safety measures are to be taken in handling pesticides and weedicides?
Answer:
Insecticides and pesticides are highly poisonous chemicals. They kill the pests. They can harm the humans also. So, certain precautionary measures should be taken while spraying pesticides and weedicides.

They should be kept away from the reach of children.
They should not be inhaled while spraying. Gloves and mouth covers should be used while spraying them.
Hands should be washed properly after their use.

Question 12.
Distinguish between pesticides and weedicides?
Answer:
Weeds are controlled by using certain chemicals called weedicides. These chemicals do not cause any damage to the crop.
Pesticides are the chemicals which are used to kill the pests growing on the crops. They kill the eggs and larvae of the insects.

Question 13.
Explain the process of harvesting?
Answer:
The removal of crop after maturity is called harvesting. The harvesting is done manually with the help of ordinary sickles in crops like wheat, paddy and maize. Even tractor driven machines are also used for harvesting wheat and paddy. Fruits and vegetables are plucked manually.

Question 14.
Explain the process of threshing,
Answer:
The crops need to be threshed to separate grains from the chaff. The mechanical harvesters help in both threshing and separating the grains. The small farmers thresh their crops by spreading the crops on the ground and walking of animals over it. Now-a-days threshing is done by threshing machines driven by tractors or electric motors, which separate grain from chaffs.

Question 15.
What factors influence the crop production?
Answer:
The factors that influence the crop production are as follow:
(i) “Soil: It is the upper layer of earth’s crust. It is the natural medium which supports plant growth.
(ii) Water: Plants require water during various stages of their growth and development such as germination, flowering, ripening, etc.
(iii) Air: Air is essential for breathing and photosynthesis.
(iv) Sunlight: It is essential for plants as a major promotion factor for photosynthesis, germination and flowering.

Question 16.
Suggest ways for the improvement of crops.
Answer:
Following ways should be adopted to improve the crops:
(i) Use of improved seeds.
(ii) Improve fertility of soil.
(iii) Protection against pests and weeds.
(iv) Better transport and storage facility.
(v) Introduction of high yielding varieties of seeds.

Long Answer Type Questions

Question 1.
What are some basic principles of crop production?
Answer:
There are certain conditions which are very important for causing the good crop yield. Good and right kind of soil, seeds, water and protection of crops from weeds and pests as well as the use of proper implements and practices- all go to determine the quality and reliability of crop yield.

A field or farm needs to be managed properly in order to get better yield. Farmers, therefore, must observe some important things which are listed below:
(i) The crop field should be open so that sunlight and air are abundantly available.
(ii) The field should be protected from stray cattle and tresspass which may destroy the crop.
(iii) The soil should be loosened and turned before sowing so that the plant roots can penetrate into it easily and are well ventilated. The latter helps in holding the plant firmly. Root and tuber crop plants need loosened soil for proper growth of the plant product.
(iv) The right amount of water should be available neither too less nor too in excess.
(v) The soil should contain sufficient nutrients for the growth of the plants.
(vi) The unwanted plants such as weeds should be removed from the soil. These weeds compete with the main plants and deprive them of their nourishment.

Question 2.
What is the use of soil for the plants?
Answer:
Soil plays an important role in agriculture in following ways:
(i) Soil fix up the plant in the soil. It holds the roots firmly and anchor the plant.
(ii) Soil has the power of retaining the water which helps the absorption by plants. It also contains minerals etc. which provides food nutrients to the plants.
(iii) It also provides space for living to useful animals such as earthworms which turn up soil and make it fertile.
(iv) Soil holds air in its gaps. This air is used by the plant for its respiration as well as for the respiration of the useful plants and bactria.

Question 3.
How are pests controlled in a crop field?
Answer:
Pests are the organisms smaller bugs which damage the crop plants in the field, during transportation, in the godowns. The common pests are birds, rats and other rodents, some animals, insects and micro-organisms belonging to different groups. They are harmful as they destroy the crop. Pests like locusts, beetles, red spiders, aphids, etc. can be controlled by three methods.
(i) Chemical control: The use of pesticides like DDT, malathion, BHC and aldrin. These chemicals are quick and effective way of controlling the growth of the pests.
(ii) Biological control: One insect feeds von other insect. In this method harmless insects are introduced in the field which will be harmful for insects and other pests.
(iii) Growing pests resistant varieties: Breeding crop varieties which are resistant to pests is a very effective and common method of pest control.

Question 4.
Why do we irrigate our crops? Explain.
Answer:
Water is required by the plants for the following activities:
(i) The seeds sown in the soil absorb water for various activities related to germination, such as activation of phenul, radicle and embryonal axis.
(ii) Water is essential for softening of soil particles so that the roots may penetrate deeply into the soil easily.
(iii) The mineral salts, manure particles, etc. dissolve in water and make the dilute solution. It is easily absorbed by the root hair.
(iv) Water is essential to maintain the turgidity of the cells and to keep them inactive form.
(v) Water is evaporated from the soil as well as from the aerial parts of the plants. Irrigation is essential to fill up the loss of water.
(vi) For the preparation of food by the plants through the process of photosynthesis, water is very essential.

Question 5.
Why an earthworm is called a friend of a farmer?
Answer:
Before sowing seeds every farmer prepares his soil for sowing. He digs the soil. He does tilling with help of tractors and ploughs. This all is done to loosen the soil particles so that air .and nutrients can be easily absorbed. Earthworm is an organism which lives under the soil and make burrows for itself. This burrowing action loosens the soil for better penetration of roots of the crops.

It create channels through the field which improves the physical properties of the soil. The burrowing action of earthworm improves soil structure, helps in formation of humus mix and till the soil and increase the supply of nutrients of the plants.

Question 6.
Write a short note of thresting and winnowing.
Answer:
When a farmer cut his crops, he has to separate the grains from the crop it is done in two ways. Manually and with machines.

The separation of seed from the crops by beating out the seeds (grain) from the crop is called threshing. It is done manually or by using threshers with combines.

After separating the grain from the harvested crop, it is required to separate grain from chaff. This process is done by winnowing. The grains are thrown from the height in the direction of air. The air carries away the lighter chaff or dried stems and leaves and the heavier grains drop down in form of a heap. This whole process is called winnowing.

Crop Production and Management Class 8 HBSE Notes

1. All living beings need food to live and perform various other activity.
2. We get food from plants and animals. The plant food is grown in fields making use of various processes. This is called agriculture.
3. All plants of same types grown together are called crops. Different types of crops are grown in the fields e.g. cereals (wheat, paddy rices) fruits and vegetables, etc.
4. Based on seasons many crops are grown. Rainy season crops are called Kharif. Winter crops are called Rabi and Summer crops are called Zayed crops.
5. To grow a crop a number of activities has to be performed. These are called agricultural practices. These agricultural practices include: soil preparation, sowing, adding manure and fertilizers, irrigation, protection from weeds, harvesting, storage, etc.
6. Preparation of soil includes loosening soil. This is called tilling or ploughing. Plough, cultivator and hoe are used as tools.
7. Sowing means putting the seeds in the loosened ground to grow.
8. For a healthy and good crop manure and fertilizers are added to the crop. These are chemicals which enhance the crop production.
9. When we grow crop in the field it takes all the nutrition away from the soil. This nutrition is – required for the next crop. The soil is replenished with nutrition by these fertilizers and manures. Crop-rotation is another method of replenishing nutrition in soil.
10. Crops are watered sufficiently by canals, drips and rainwater. This is called irrigation of crops. Irrigation is the most important process of crop production.
11. Undesirable plants growing among the crops are removed manually or by machines. These unwanted plants are called weeds, chemicals used to kill weeds are Called weedicides.
12. Sometimes some small animals start eating the crops. These are called pests. Special chemicals
are sprayed on the crops to kill the pests. These chemicals are called pesticides.
13. After the crops are ready, they are harvested. Grains are separated from the chaff. This process is called threshing. Threshers are used to do this process.
14. The harvested grains are then Stored in huge stores, after they are properly dried in sun. These stores kre called granaries.
15. We also get our food from animals. For this purpose some useful animals are domesticated
and reared. This is called Animal Husbandry. Animals like cows, buffaloes, goats, hens etc. are domesticated for food.

Haryana State Board HBSE 8th Class Science Solutions Chapter 18 Pollution of Air and Water Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 18 Pollution of Air and Water

HBSE 8th Class Science Pollution of Air and Water Textbook Questions and Answers

Question 1.
What are the different ways in which water gets contaminated?
Answer:
Water gets contaminated by the following ways:

• Water gets contaminated when sewage is disposed off in rivers.
• Chemicals which are harmful and poisonous are thrown in water resources by various industrial units.
• Harmful chemicals used in agricultural process gets mixed with ground water making it unfit for consumption.
• Breeding of microorganisms in water make water polluted.

Question 2.
At an individual level, how can you help reduce air pollution?
Answer:
We can plant tree to reduce the level of carbon dioxide. We can get our vehicles serviced well to reduce uncomplete consumption of fuels. We can also reduce air pollution by saying no to crackers during Diwali celebrations.

Question 3.
Clear, transparent water is always fit for drinking. Comment.
Answer:
Water which is clear and through which we can see is fit for consumption because this type of water is free from pollutants. Transparent water means no microorganisms and no dust particles.

Question 4.
You are a member of the municipal body of your town.
Make a list of measures that would help your town to ensure the supply of clean water to all its residents.
Answer:

• To get clean water in every household, it is necessary that water reaching houses should be treated water. Water is treated in sewage plants, to make it free from physical, chemical and biological impurities.
• Strict laws should be enforced on industrial units, which dispose polluted water in water resources.
• Open defecation in water resources by slum dwellers should be strictly prohibited.
• Chlorine tablets should be distributed for purification of water during rainy season.
• People should be made aware and motivated to keep water resources clean.

Question 5.
Explain the differences between pure air and polluted air.
Answer:
Pure air is free from harmful gases which can be poisonous in nature. Pure air has balanced quantity of all its constituent gases and it is free from other germs. This type of air is fit for breathing. On the other hand polluted air has poisonous gases and other suspended impurities like dust and smoke. It is unfit for consumption.

Question 6.
Explain circumstances leading to acid rain. How does acid rain affect us?
Answer:
Acid rain is caused due to mixing of poisonous gases with rain. When our industrial units emit poisonous gases like sulphur dioxide and nitrogen dioxide, these gases react with moisture present in air and form nitric acid and sulphuric acid. These acids fall on the earth with rain making rain water acidic and harmful.

Acid rain causes the corrosion of buildings and make food grains, fruits and vegetables on which it fall, unfit for consumption.

Question 7.
Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen
Answer:
Sulphur dioxide.

Question 8.
Describe the ‘Green House Effect’ in your own words.
Answer:
Green house effect means warming the environment. When the rays of sun reach earth, some of the heat is absorbed by the earth. Rest of it is reflected back by the earth. Some of the heat is trapped by the environment of the earth. This causes warming of the environment, which is necessary for the sustaining life. This trapping of the heat is called green house effect.

Question 9.
Prepare a brief speech on global warming. You have to deliver the speech in your class.
Answer:
Continuous increase in the temperature of the earth is called global warming. It it caused by the pollution of air, excessive heat trapped by the green house gases, because the amount of green house gases has increased in the environment. Global warming is a threating phenomenon because we may have to face dire consequences due to Global warming.

Question 10.
Describe the threat to the beauty of the Taj Mahal.
Answer:
Increasing air pollution has posed a threat to the beauty of the Taj Mahal. Excessive poisonous gases and smoke has started to discolour the white marble of the Taj Mahal. Acid rains due to increasing air pollution has started to corrode the marble, thus making Taj Mahal loose its beauty.

Question 11.
Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
Answer:
Addition of nutrients in water flourishes the growth of microorganisms like algae. When these microorganisms die, they become food of bacteria. When bacteria become active, they consume a lot of oxygen present in water. Decrease in oxygen in water, becomes trouble for other aquatic animals and they start dying due to insufficient amount of oxygen to breath.

Extended Learning – Activities and Projects

Question 1.
In some cities, a pollution check has been made compulsory for vehicles. Visit a petrol pump in order to learn about the process of conducting a pollution check. You may systematically record your findings in the following areas:
(i) Average number of vehicles checked per month.
(ii) Time taken to check each vehicle.
(iii) Pollutants checked for.
(iv) The process of testing.
(v) Permissible levels of emission of various gases.
(vi) Measures taken if the emitted gases are above the permissible limits.
(vii) How frequently is a pollution check required?
Answer:
For self attempt.

Question 2.
Conduct a survey in your school to investigate various environment related activities that have been undertaken. The class can divide itself into two groups, with each group looking at a different area. For example, one group can find out whether there is an environment club in the school. What are its objectives? What is its calendar of events? How can you become a member?
If your school does not have such a club, you can even think of starting one along with a few of your friends.
Answer:
For self attempt.

Question 3.
Organise a field visit to a river in or around your town with the help of your teachers. Observations followed by discussion could focus on:
(i) The history of the river.
(ii) Cultural traditions.
(iii) Role of the river in meeting the town’s water needs.
(iv) Pollution concerns.
(v) Sources of pollution.
(vi) Effects of pollution on the people living by the riverside as well as those living far away.
Answer:
For self attempt.

Question 4.
Find out with the help of your teachers and the internet (if possible), whether there are any international agreements to control global warming. Which are the gases covered under these agreements?
(i) www.edugreen.teri.res.in/explore/air/ air.htm
(ii) www.edugreen.teri.res.in/explore/water/ pollu.htm
(iii) www.cpcb.nic.in/citizen’s%Charter/ default_citizen’s.html
(iv) coe.mse.ac.in/kidswater.asp
(v) coe.mse.ac.in/kidsair.asp
Answer:
For self attempt.

HBSE 7th Class Science Pollution of Air and Water Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is a pollutant?
Answer:
Pollutant is an undesired and harmful substance.

Question 2.
What is air pollution?
Answer:
Addition of pollutants to air is called air pollution.

Question 3.
Name any two air pollutants.
Answer:
Smoke and sulphur dioxide.

Question 4.
Name any two natural pollutants.
Answer:
Forest fire and erruption in volcanoes.

Question 5.
What is smog?
Answer:
Mixture of smoke and moisture is called smog.

Question 6.
Name two chemicals causing acid rains.
Answer:
Sulphur dioxide and nitrogen dioxide.

Question 7.
Which gas is responsible for depletion of ozone layer?
Answer:
Chlorofluorocarbon.

Question 8.
Where CFC is used?
Answer:
CFC is used for refrigeration.

Question 9.
What effect does acid rain has on building?
Answer:
It corrodes the buildings.

Question 10.
Name any two green house gases.
Answer:
Methane and carbon dioxide.

Question 11.
Which phenomenon causes global warming?
Answer:
Green house effect.

Question 12.
Write any one harmful effect of global warming.
Answer:
It can cause flood by melting glaciers.

Question 13.
Which is the main constituent gas of air?
Answer:
Nitrogen about 78%.

Question 14.
What is the percentage of oxygen in air?
Answer:
21%.

Question 15.
Which industry is the main source of gaseous pollutants like sulphur dioxide and nitrogen dioxide?
Answer:
Petroleum refineries.

Question 16.
From what does the ozone layer – protect us?
Answer:
Ozone layer protects us from ultraviolet rays of sun.

Question 17.
What reduces the visibility in air?
Answer:
Small suspended particles emitted by automobiles using diesel as fuel.

Question 18.
Which refinery is producing pollutants near the Taj Mahal?
Answer:
Mathura oil refinery.

Question 19.
What is Marble cancer?
Answer:
Corrosion of marble due to acid rain is called marble cancer.

Question 20.
Which fuel is being used as the pollution free fuel?
Answer:
CNG and LPG.

Question 21.
What is trapping of radiations of sun by the atmosphere of the earth, called?
Answer:
Green house effect.

Question 22.
Which gas is mainly the green house gas?
Answer:
Carbon dioxide.

Question 23.
Which substances pollute water?
Answer:
Sewage, toxic chemicals, silt etc.

Question 24.
Name the Indian river which is considered as one of the ten most polluted rivers in world?
Answer:
Ganga.

Question 25.
What pollutes Ganga?
Answer:
Untreated sewage, dead bodies, garbage etc.

Question 26.
What is the plan, implemented to save Ganga, called?
Answer:
Ganga Action Plan.

Question 27.
Which chemicals released in water leads to toxicity in animals and plants?
Answer:
Arsenic, lead and fluorides.

Question 28.
What do you mean by potable water?
Answer:
Water which is suitable for drinking is called potable water.

Question 29.
Which chemical is used to purify water?
Answer:
Chlorine.

Question 30.
Which physical qualities should we look for in drinking water?
Answer:
Clearness, transparency and odour.

Short Answer Type Questions

Question 1.
Describe what is pollution.
Answer:
Pollution can be described as addition of unwanted and undesired harmful substances in any natural resource. Addition of these substances spoil the natural resources and make them unfit for consumption by men and other living beings. Air pollution, water pollution, soil pollution etc. are various types of pollutions.

Question 2.
Describe air pollution.
Answer:
Addition of poisonous and harmful substances in air is called air pollution. Air gets polluted when poisonous gases like sulphur dioxide, nitrogen dioxide and other oxides of nitrate get mixed up in air. It is also polluted by smoke emitted by industries using coal and also the smoke emitted by vehicles.

Question 3.
Write any three causes of air pollution.
Answer:
Following are various causes of air pollution:

• Smoke emitted due to fires in forests.
• Poisonous gases expelled the various industries.
• Poisonous gases emitted by vehicles using petroleum fuels.

Question 4.
What is smog? How is it produced?
Answer:
In winters, we can see a fog like dark layer in the mornings and nights. It reduces the visibility. This is called smog. Smog means fog plus smoke. It is formed due to combination of oxides of mitrates with fog. Various vehicles and industries produce smoke and the nitrates. Thus smog is formed.

Question 5.
What is ozone? How is it helpful for our environment?
Answer:
Ozone is a gas which is very helpful for environment of our earth. It forms a protective layer around the atmosphere of earth. It does not allow the ultraviolet rays of the sun from reaching the earth. U.V. rays can cause great damage to our earth. So, ozone is of great help for our earth.

Question 6.
What is ozone hole or depletion of ozone layer?
Answer:
A gas named ozone forms a protective layer around the atmosphere of the earth. It protects the earth from the ultra-violet rays of the sun. But some chemicals used in refrigeration causes damage to this layer. CFCs cause tearing away of this layer. This is called depletion of ozone layer. At some points, this layer is depleted completely and holes are created. These holes are called ozone holes.

Question 7.
What are the harmful effects of air pollution?
Answer:
Air pollution cause many diseases in human beings. Respiratory diseases are commonly caused by air pollution. It causes harm to our building and monuments. It reduces visibility as smog and causes many serious accidents.

Question 8.
How is acid rain caused?
Answer:
When rain water becomes acidic in nature, it is called the acid rain. Different industries produce pollutants like sulphur dioxide and nitrogen dioxide. These gases react with moisture and produce sulphuric acid and nitric acid. These acids fall on earth along with rain and this is called acidic rain.

Question 9.
What steps has. Honourable Supreme Court taken to save the Taj Mahal from air pollution?
Answer:
The Supreme Court has given orders that cleaner fuel be used in the near about areas of the Taj Mahal. Fuels like CNG and LPG are considered clean fuel. Moreover petrol should be free from lead. This is called unleaded petrol. Only unleaded petrol can be used in areas near the Taj Mahal.

Question 10.
What is the Green House effect?
Answer:
The sun sends its rays to the earth. Some of these rays are absorbed by the earth and some radiations are reflected back by the earth. Thes reflected radiations are not allowed to leave earth’s atmosphere completely. Some of these radiations are trapped by the earth’s atmosphere and this is called the green house effect.

Question 11.
What is global warming? How is it caused?
Answer:
Increasing temperature of the earth is called global warming. The radiation of the sun, reaching the earth is not being consumed. This is due to the deforestation. The level of CO₂ has increased and thus global warming has also increased. CO₂ is absorbed by the plants for photosynthesis. So reduced number of plants increases the amount of carbon dioxide in the environment, this causes accumulation of carbondioxide and increases temperature.

Question 12.
How does water get polluted?
Answer:
Water gets polluted when unwanted and harmful chemical substances are added to the water. Untreated sewer and garbage is also added to water resources to pollute water. All these chemicals make water unfit for usage.

Long Answer Type Questions

Question 1.
What is air pollution? How is it caused?
Answer:
When poisonous gases, dirt and smoke get added in the water it pollutes the air and it is called air pollution. Following factors are responsible for air pollution.
(i) Industrial Emissions : Various dangerous and poisonous gases emitted by different industries cause air pollution. Industries using coal and other petroleum products as fuel emit poisonous gases like sulphur dioxide and nitrogen dioxide. These gases further react with moisture present in environment and form their respective acids. These acids along with rain water cause acid rains.

(ii) Vehicles : Unburnt carbon particles emitted by vehicles due to incomplete combustion cause severe air pollution. It contains gases like carbodioxide and carbon monoxide which is highly poisonous. Unburnt carbon particles emitted as smoke also cause phenomenon like smog which reduce visibility besides causing air pollution.

(iii) Natural Pollutant: Natural pollutants like forest fire, volcanic erruption, dust storms etc. also cause air pollution to some extent.

(iv) Other activities of Man : Besides above described causes many other human activities also add to air pollution. Using fuels like cow dung, coal, wood etc. at home for domestic use also pollute the air. Agricultural practices like burning chaff after cultivation etc. also pollute the air. A lot of air pollution is caused due to burning of crackers on Diwali and other celebrations.

Question 2.
How is water pollution caused?
Answer:
Water pollution is caused by many factors. These pollutants are described below :
(i) Industrial discharges: Various harmful and poisonous chemicals are discharged by various industries directly into water bodies. These chemicals when added in water, spoil it and render it unfit for consumption by living beings.

(ii) Domestic discharges : Sewage from homes are collected and disposed off in rivers nearby. This untreated sewage is one of the prominent causes of water, pollution.

(iii) Religious Rituals : Various religious rituals of different religions also add to certain extent to the water pollution.

Dispersion of dead bodies or remains of dead bodies in rivers is causing pollution of water. Various other materials are also dispersed in water after performing some rituals. These also make water dirty.

(iv) Other Human activities : Apart from above cited reasons, water is also polluted due to certain other human activities. People wash their clothes on banks of rivers. They take their livestock to rivers for their bathing. They throw their wastage in water bodies and sometimes defecate in open at the banks of rivers. This makes water polluted and unfit for human consumption.

Question 3.
What measures should be taken to control air pollution and water pollution?
Answer:
Air pollution and water pollution are causing a great threat for the human civilization. We should seriously work to control them. Following measures can help us in controlling air and water pollution :
(i) All industrial units should use cleaner fuels and should not release their harmful 4 emission directly into air or water.

(ii) All industrial units throwing their harmful waste products in water, should install treatment or purification plants in their premises so that only treated and purified waste should be released in water bodies.

(iii) All the sewages of cities and villages should treated to destroy harmful physical, chemical and biological impurities before releasing it in water resources.

(iv) All vehicles should use pollution free fuels like CNG, LPG and unleaded petrol. Vehicles should be serviced well to avoid incomplete combustion of fuel.

(v) Smokeless fuels should be provided for domestic usage.

(vi) Electrical crematoriums should be made in all cities as well as in villages.

Question 4.
What are the various harmful effects of air and water pollution?
Answer:
(i) Air and water pollution are both dangerous for human health. They cause various diseases, which are the result of harmful emissions and discharges in air and water. Water brone diseases like Cholera, Typhoid, Infections, etc. are caused. Air pollution causes various respiratory diseases like asthma, allergies and lung cancer etc.

(ii) These pollutions also cause troubles for animals. Water pollution destroy the aquatic life as it causes deficiency of oxygen in water causing death of aquatic animals.

(iii) Various environmental problems like global warming are result of air pollution. Due to increase in level of carbon dioxide, the radiations of sun are not allowed to leave our environment. They get trapped in our environment and temperature of earth gets increased. This is called global warming.

(iv) Fresh and consumable water is getting reduced day by day as water resources are getting polluted very rapidly.

(v) Phenomena like smog, marble-cancer etc. are causing threat to our property and life.

Pollution of Air and Water Class 8 HBSE Notes

• Addition of unwanted and poisonous substances in air or water is called their respective pollutions.
• Air and water pollution has increased in recent past with industrialization and urbanization.
• Air is a mixture of gases mainly the nitrogen, oxygen and carbon dioxide when any of the harmful gases increase in its percentage, it makes the air polluted.
• Emission of smoke in industries, smoke due to forest fires and smoke emitted by vehicles pollutes the air.
• Smoke, dust of harmful gases emitted during volcanic erruptions, or forest fires or due to dust storms etc. are called the natural air pollutents.
• Unburnt fuel of the vehicles is one of main cause of air pollution.
• Air pollution can give rise to different ailments in human beings. Oxides of nitrogen can cause asthma, cough and wheezing. It can even cause cancer of lungs.
• Pollutants like sulphur dioxide, nitrogen oxide are emitted by industries.
• Gases used in refregeration also cause depletion of ozone layer, which cause further environmental problems like global warming.
• Non-living objects are also effected by air pollution. Discolouring of white marble of Taj Mahal is an example.
• Deforestation is one of the main cause of air pollution because less amount of carbon dioxide is absorbed by the plants and its amount increases in atmosphere resulting in global warming.
• Addition of undesirable substances like sewage, harmful chemicals etc. to the water cause water pollution.
  Polluted water becomes unfit for consumption.
• Water is purified before consuming it.

Haryana Board HBSE 8th Class Science Solutions

HBSE 8th Class Science Solutions in English Medium

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: Metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Combustion and Flame
• Chapter 7 Conservation of Plants and Animals
• Chapter 8 Cell Structure and Functions
• Chapter 9 Reproduction in Animals
• Chapter 10 Reaching the Age of Adolescence
• Chapter 11 Force and Pressure
• Chapter 12 Friction
• Chapter 13 Sound
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water

HBSE 8th Class Science Solutions in Hindi Medium

• Chapter 1 फसल उत्पादन एवं प्रबंध
• Chapter 2 सूक्ष्मजीव: मित्र एवं शत्रु
• Chapter 3 संश्लेषित रेशे और प्लास्टिक
• Chapter 4 पदार्थ: धातु और अधातु
• Chapter 5 कोयला और पेट्रोलियम
• Chapter 6 दहन और ज्वाला
• Chapter 7 पौधे एवं जंतुओं का संरक्षण
• Chapter 8 कोशिका – संरचना एवं प्रकार्य
• Chapter 9 जंतुओं में जनन
• Chapter 10 किशोरावस्था की ओर
• Chapter 11 बल तथा दाब
• Chapter 12 घर्षण
• Chapter 13 ध्वनि
• Chapter 14 विधुत धारा के रासानिक प्रभाव
• Chapter 15 कुछ प्राकृतिक परिघटनाएँ
• Chapter 16 प्रकाश
• Chapter 17 तारे एवं सौर परिवार
• Chapter 18 वायु तथा जल का प्रदूषण