Class 7

Haryana State Board HBSE 7th Class Science Solutions Chapter 12 Reproduction in Plants Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 12 Reproduction in Plants

HBSE 7th Class Science Reproduction in Plants Textbook Questions and Answers

Question 1.
Fill in the blanks :
(a) Production of new individuals from the vegetative part of parent is called _________.
(b) A flower may have either male or female reproductive parts. Such a flower is called _________.
(c) The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as _________.
(d) The fusion of male and female gametes is termed as _________.
(e) Seed dispersal takes place by means of _________ and _________.
Answer:
(a) vegetative reproduction,
(b) bisexual flower
(c) pollination
(d) fertilization,
(e) wind, water, insects.

Question 2.
Describe the different methods of asexual reproduction. Give examples.
Answer:
Different methods of asexual reproduction are :
(a) Binary fission : This process takes place in unicellular organisms. Parent cell elongates and get divided into two identical daughter cells. Each daughter cell grows into an independent adult, e.g. in case of bacteria.

(b) Endospore formation : In this method a spore wall is formed around a bacterial cell to form an endospore. This endospore germinates to form an active bacterium under favourable conditions.

(c) Fragmentation : This occurs mainly in Algae. Body of the organism breaks up into two parts. Then each part grows into a new filament thus forming two organisms from a single one.

(d) Spore formation : The spores are tiny, spherical unicellular structures protected by a thick wall. The spores are stored in a hard outer covering and this is called sporangia. Under favourable conditions the hard cover breaks and spores spread for germination.

(e) Budding : In yeast, new organisms are produced by the bud formation from the parent organism. After growing to full size, the bud gets detached and form a new independent individual.

(f) Vegetative reproduction : When vegetative part of a plant like stems, leaves and root etc. give rise to new ones, it is called vegetative reproduction.

Question 3.
Explain what do you understand by sexual reproduction?
Answer:
Sexual reproduction means involvement of two parents in the process of reproduction. It is found mainly in higher plants. Male gamete and female gamete fuse to form a zygote. These zygotes develop into individuals which are not identical. Offspring inherit the characteristics of both the parents. In sexual reproduction both parents survive after the process of reproduction.

Question 4.
State the main differences between asexual and sexual reproduction.
Answer:

Question 5.
Sketch the reproductive parts of a flower.
Answer:

Question 6.
Explain the difference between self-pollination and cross-pollination.
Answer:

Question 7.
How does the process of fertilization take place in flowers?
Answer:
When the pollen grain reaches the stigma of a same flower, it starts growing out in pollen tube of the stigma. This tube continues to grow inside the style till it reaches the ovule. Male cells are released in the ovule for the fertilization with female cells and thus the zygote is formed. After this process of fertilization, the ovary develops into fruit and ovule into seeds.

Question 8.
Describe the various ways by which seeds are dispersed.
Answer:
Following are the ways in which the seeds get dispersed:
(i) Some light seeds like that of Madar, which are hairy, dry and small are carried away by the wind to different places. Some seeds having winged structure e.g. that of Maple and Drumstick are also dispersed by air.

(ii) Spiny seeds and fruits like that of Xanthium and Gokhru, the seeds stick to the clothes of passers-bye and animals. These seeds are carried away by these agents to different places.

(iii) In some cases having heavy seeds like that of Coconut, water acts as the dispersing agents.

(iv) Some seeds are diprersed when the fruit bursts like in case of Balsam and castor.

Question 9.
Match the items in Column I with those of Column II :

Answer:
(a) (iii)
(b) (v)
(c) (ii)
(d) (i)
(e) (iv)

Question 10.
Tick (✓) the correct answer :
(a) The reproductive part of a plant is the :
(i) Leaf
(ii) Stem
(iii) Root
(iv) Flower
Answer:
(iv) Flower

(b) The process of fusion of the male and the female gametes is called :
(i) fertilization
(ii) Pollination
(iii) reproduction
(iv) seed formation
Answer:
(i) fertilization

(c) Mature ovary forms the:
(i) Seed
(ii) Stamen
(iii) Pistil
(iv) Fruit
Answer:
(iv) Fruit

(d) A spore producing plant is :
(i) Rose
(ii) Bread mould
(iii) Potato
(iv) Ginger
Answer:
(ii) Bread mould

(e) Bryophyllum can reproduce by its :
(i) Stem
(ii) Leaves
(iii) Roots
(iv) Flower
Answer:
(ii) Leaves

Extended Learning-Activities and Projects

Question 1.
Make your own cactus garden by collecting pieces cut from different kinds of cacti. Grow the variety in one single flat container or in separate pots.
Answer:
Do it yourself.

Question 2.
Visit a fruit market and collect as many local fruits as possible. If many fruits are not available, you can collect tomatoes and cucumbers (these are fruits, though we use them as vegetables). Make drawings of the different fruits. Split the fruits and examine the seeds within. Look for any special characteristics in the fruits and their seeds.
Answer:
Do it yourself.

Question 3.
Think of ten different fruit-bearing plants. Remember that many vegetables are also fruits of the plants. Discuss with your teacher, parents, farmers, fruit growers and agricultural experts (if available nearby) and find out the manner of their dispersal. Present your data in the form of a table as shown below :

Answer:
Do it yourself.

Question 4.
Suppose there is one member of a particular kind of organism in a culture dish, which doubles itself in one hour through asexual reproduction. Work out the number of members of that kind of organism which will be present in the culture dish after ten hours. Such a colony of individuals arising from one parent is called a “clone”.
Answer:
Do it yourself.

HBSE 7th Class Science Reproduction in Plants Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What do you understand by the term reproduction?
Answer:
Reproduction is the process by which the living organisms produce more of their ownkind.

Question 2.
Name the methods by which plants reproduce.
Answer:
Plants reproduce in two ways :

• Asexual reproduction
• Sexual reproduction.

Question 3.
What is pollination?
Answer:
Pollination is a process in which pollen grains get transferred from anther to the stigma of the‘flower.

Question 4.
Name different methods of asexual reproduction.
Answer:
Various methods of asexual reproduction are :

• Binary fission
• Endospore formation
• Fragmentation
• spore formation
• Budding
• Vegetative reproduction.

Question 5.
What do you mean by the term fertilization?
Answer:
Fertilization is a process in which fusion of male and female gametes takes place to produce the zygote.

Question 6.
What is vegetative reproduction?
Answer:
It is the simplest method of reproduction in plants. In this method the vegetative parts like stem, roots and leaves produce new ones.

Question 7.
What is the advantage of the vegetative reproduction?
Answer:
The vegetative reproduction occurs very fast and easily. So quick reproduction is possible.

Question 8.
What is difference between unisexual and bisexual flowers?
Answer:
Unisexual flower has either a male or female reproductive part and bisexual flower has both of them.

Question 9.
Write any one advantage of seed dispersal.
Answer:
It prevents the plants from competing for sunlight, water and minerals.

Question 10.
Where are the male and female gametes found?
Answer:
The male gametes are found inside the pollen grains and the ovule contains the female gametes.

Short Answer Type Questions

Question 1.
What is reproduction? Name various methods of reproduction in plants.
Answer:
Reproduction is the process by which the living organisms produce more of their ownkind. Plants reproduce by two methods asexual and sexual. Asexual reproduction means the birth of new ones by single parent only. Sexual reproductions means involvement of two parents in the process.

Question 2.
List the different methods of asexual reproduction. In which type of plants does asexual reproduction occur?
Answer:
Asexual reproduction occurs in lower form of plants, where they do not have any reproductive part. It occurs through following methods.

• Binary fission
• Budding
• Endospore formation
• Spore formation
• Fragmentation
• Vegetative reproduction.

Question 3.
What is pollination? How is it brought about?
Answer:
The transfer of pollen grains from anther to stigma of a flower is called pollination. Pollination is brought about by many agents like water, air, animals and insects. Pollen grains are carried by these agents from anther of one flower to the stigma of another flower of same kind.

Question 4.
What do you mean by cross-pollination and self-pollination?
Answer:
Transfer of pollens occur in two ways. When pollen grains ate transferred to stigma of the same flower, it is called self pollination. When transfer of pollen grains take place from anther of one flower to the stigma of another flower of same kind, it is called cross pollination.

Question 5.
Write a short note on vegetative propagation.
Answer:
Vegetative reproduction! means the birth of new ones from the vegetative parts of the plant like leaves, stem, roots and buds. This is an asexual type of reproduction. Eyes on potato, buds sprouting on the leaves of bryophyllum, new plant growing out of cactus’ stem etc are examples of vegetative reproduction.

Question 6.
Write atleast three advantages of vegetative propagation methods.
Answer:
Following are the advantages of vegetative propagation:

• It is a fast method of reproduction.
• Plants produced by vegetative propagation have same features as that of parent plant.
• Plants produced by vegetative reproduction bear flowers and fruits earlier than the plants grown out of seeds.

Long Answer Type Questions

Question 1.
What is Asexual reproduction? Explain various methods of asexual reproduction.
Answer:
Asexual reproduction means obtaining new plants from one parent without seeds. Various methods of asexual reproduction are as follows :

Different methods of asexual reproduction are :
(a) Binary fission : This process takes place in unicellular organisms. Parent cell elongates and get divided into two identical daughter cells. Each daughter cell grows into an independent adult, e.g. in case of bacteria.

(b) Endospore formation : In this method a spore wall is formed around a bacterial cell to form an endospore. This endospore germinates to form an active bacterium under favourable conditions.

(c) Fragmentation : This occurs mainly in Algae. Body of the organism breaks up into two parts. Then each part grows into a new filament thus forming two organisms from a single one.

(d) Spore formation : The spores are tiny, spherical unicellular structures protected by a thick wall. The spores are stored in a hard outer covering and this is called sporangia. Under favourable conditions the hard cover breaks and spores spread for germination.

(e) Budding : In yeast, new organisms are produced by the bud formation from the parent organism. After growing to full size, the bud gets detached and form a new independent individual.

(f) Vegetative reproduction : When vegetative part of a plant like stems, leaves and root etc. give rise to new ones, it is called vegetative reproduction.

Question 2.
What is vegetative reproduction ? Describe vegetative reproduction in different parts of the plant.
Answer:
Vegetative reproduction means growing of off springs from the vegetative parts of the plant like roots, stems, and leaves.
(i) Vegetative propagation by roots : Thick roots of sweet potato, dahlia or asparagus give rise to new ones, inside the soil only.

(ii) Vegetative propagation by stems : In certain plants like potato, ginger, sugarcane etc, new plants grow from the stems of these plants. In potatoes these are small ‘eyes’ on the swollen stem. These eyes germinate to give rise to new plants. Ginger and turmeric also give rise to new plants rom the small buds growing on their swollen stems.

(iii) Vegetative reproduction by leaves : In plants like Bryophyllum Small plantlets grow from the margins of the leaves. These plantlets when detached from the leaf and grown develops into an independent plant.

Question 3.
Explain Sexual Reproduction in plants.
Answer:
Sexual reproduction occurs in plants having well developed reproductive parts in them. Flowers are the reproductive parts of the plant. Flowers can be unisexual i.e. having only male or female reproductive parts, and Bisexual i.e. having both male and female reproductive parts.

Female reproductive part of the flower i.e. the pistil form female ovules and male reproductive parts i.e. Androecium give rise to male gametes. When male and female gametes fuse in the ovary of the flower the process of fertilisation takes place. Male gametes are carried to the female flowers far away by agents like wind, water, insects and animals. This is called pollination. After fertilization the ovary of the flower becomes pulpy and juicy to form fruits. The ovules become the seeds.

Reproduction in Plants Class 7 HBSE Notes

• Reproduction is the process by which all the living organisms produce more of their own kind.
• The reproduction in plants occur by two methods : asexual reproduction and sexual reproduction.
• Asexual reproduction is reproduction without seeds involving only single parent.
• Asexual reproduction occurs in lower forms of the plants.
• Various methods of asexual reproduction are : Binary fission, fragmentation, Endospore formation, spore formation, Budding and vegetative reproduction.
• Binary fission is division of elongated parent cell into two daughter cell. It mostly occurs in bacteria. Some bacteria reproduce by endospore formation.
• Fragmentation is splitting up of filaments of algae in two or more than two parts, which develop into complete organism.
• Spores are formed in fungi, spores along with outer hard covering are called sporangium. Sporangium burst to release spores.
• Bud is a small bulb like projection, which comes out of yeast cell. It grows and detach from the parent cell to form a new yeast cell.
• Vegetative propagation is the birth of new ones from the vegatative parts of the plant like leaves, roots, stems etc.
• Sexual reproduction is the reproduction by seeds involving both male and female plants.
• Male and female gametes fuse to form zygote which grows into a developed new plant.
• Ovaries of the plant develop into fruit after fertilization and ovules becomes seeds.
• Male pollen grains are transferred from one flower to another and this is called pollination.
• When pollen grain of same flower are transferred from anther to stigma of same flower, it is called self-pollination.
• When pollens of a flower are transferred to stigma of another flower of same kind, it is called cross-pollination.

Haryana State Board HBSE 7th Class Science Solutions Chapter 7 Weather, Climate and Adaptations of Animals to Climate Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 7 Weather, Climate and Adaptations of Animals to Climate

HBSE 7th Class Science Weather, Climate and Adaptations of Animals to Climate Textbook Questions and Answers

Question 1.
Name the elements that determine the weather of a place.
Answer:
The temperature, humidity, rainfall, wind-seed, etc. are called the elements of the weather, that determine the weather of a place.

Question 2.
When are the maximum and minimum temperature likely to occur during the day?
Answer:
The maximum temperature of the day occurs generally in the afternoon while the minimum temperature occurs generally in the early morning.

Question 3.
Fill in the blanks:
(i) The average weather taken over a long time is called ………… .
(ii) A place receives very little rainfall and the temperature is high throughout the year, the climate of that place will be………….. and ………….. .
(iii) The two regions of the earth extreme climatic conditions are …………… and ……………. .
Answer:
(i) the climate of the place
(ii) hot, dry
(iii) polar, tropical

Question 4.
Indicate the type of climate of the following areas:
(a) Jammu and Kashmir
(b) Kerla
(c) Rajasthan
(d) North-East India.
Answer:
(a) Jammu and Kashmir – moderately hot and moderately wet climate
(b) Kerala – very hot and wet climate
(c) Rajasthan – hot and dry climate
(d) North-east India – The north eastern India receives rain for a major part of the year. Therefore, we can say that the climate of the north-east is wet.

Question 5.
Which of the two changes frequently, weather or climate?
Answer:
Weather.

Question 6.
Following are some of the characteristics of animals:
(i) Diets heavy on fruits
(ii) White fur
(iii) Need to migrate
(iv) Loud Voice
(v) Sticky pads on feet
(vi) Layer of fat under skin
(vii) Wide and large paws
(viii) Bright colours
(ix) Strong tails
(x) Long and large beak
For each characteristic indicate whether it is adaptation for tropical rainforests or polar regions. Do yQU think that some of these characteristics can be adaptations for both the regions?
Answer:
(i) Diets heavy on fruits – tropical rainforests
(ii) White fur – polar regions
(iii) Need to migrate – pblar regions
(iv) Loud Voice – tropical rainforests
(v) Sticky pads, on feet – tropical rainforests
(vi) Layer of fat under skin – polar regions
(vii) Wide and large paws – polar Regions
(viii) Bright colours – tropical rainforests
(ix) Strong tails – tropical regions
(x) Long and large beak – tropical rainforests.

Question 7.
The tropical rainforests has a large population of animals. Explain why it is so?
Answer:
The tropical region has generally a hot climate because of its location around the equator. Even in the coldest month the temperature is generally higher than about 15°C. During hot summers, the temperature may cross 40°C. Days and nights are almost equal in length throughout the year. These regions get plenty of rainfall.

An important feature of this region is the tropical rainforests. Tropical rainforests are found in Western Ghats and Assam in India, South East Asia, Central America and Central Africa. Because of continuous warmth and rain, this region support wide variety of plants and animals. The major types of animals living in the rainforests are monkeys, apes, gorillas, lions, tigers,, elephants, leopards, lizards, snakes, birds and insects.

Question 8.
Explain, jirith examples, why we find animals of certain kind living in particular climatic conditions?
Answer:
Animals are adapted to survive in the conditions in which they live. Animals living in very cold and hot climate must possess special features to protect themselves against the extreme cold or heat.

Penguins are found in cold regions. They have a feathery coat as well as a layer of fat under the feathery coat. The coat covers their bodies right down to their legs. These adaptations keep the body warm.

Polar bear Eire found in the Arctic region where it is very cold. They have a thick layer of fur Emd a lot of fat in their bodies to keep them warm. Their soles are covered with fur to keep them warm. The white fur also helps the polar bears to blend with the snowy surroundings so that they are detected by the prey.!

Question 9.
How do elephant living in the tropical! rainforest adapt itself
Answer:
It has adapted to the conditions of rainforests in many remarkable ways. Trunks uses it as a nose because of which it has a strong sense of smell. The trunk is also used by it for picking up food. Moreover, its tusks are modified teeth. These can tear the bark of trees that elephant loves to eat. So, the elephant is able to handle the competition for food rather well. Large ears of the elephant help it to hear even very soft sounds. They also help the elephant to keep cool in the hot and humid climate of the rainforest.

Choose the correct option which answers the following questions (Question 10-12).

Question 10.
A carnivore with stripes on its body moves very fast while catching its prey. It is likely to be found in:
(i) polar regions
(ii) deserts
(iii) oceans
(iv) tropical rainforests
Answer:
(iv) tropical rainforests

Question 11.
Which features adapt polar bears to live in extremely cold climate?
(i) A white fur, fat below skin, keen sense of smell.
(ii) Thin skin, large eyes, a white fur.
(iii) A long tail, strong claws, white large paws.
(iv) White ‘body, paws for swimming, gills for respiration.
Answer:
(i) A white fur, fat below skin, keen sense of smell.

Question 12.
Which option best describes a tropical region?
(i) hot and humid
(ii) moderate temperature, heavy rainfall
(iii) cold and humid
(iv) hot and dry
Answer:
(i) hot and humid

Extended Learning – Projects And Activities

Question 1.
Collect weather reports of seven successive days in the winter months (Preferably December). Collect similar reports for the summer months (Preferably June). Now prepare a Table for sunrise and sunset times as shown:

Try to answer the following questions:

• Is there any difference in the time of sunrise during summer and winter?
• When do you find that the sun rises earlier?
• Do you also find any difference in the time of sunset during the month of June and December?
• When are the days longer?
• When are the nights longer?
• Why are the days sometimes longer and sometimes shorter?
• Plot the length of the day against the days chosen in June and December. (Instructions for plotting graphs are given in Chapter 13).
  Answer:
  Do yourself.

Question 2.
Collect information about the Indian Meteorological Department. If possible visit its website: htt/www.imd.gov.in.
Write a brief report about the things this department does.
Answer:
Do yourself.

HBSE 7th Class Science Weather, Climate and Adaptations of Animals to Climate Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is raingauge?
Answer:
Rainfall is measured by an instrument called the rainguage. It is basically a measuring cylinder with a funnel on top to collect rainwater.

Question 2.
Define weather.
Answer:
The day-to-day condition of the atmosphere at,’a place with respect to the temperature, humidity, rainfall, wind speed, etc., is called the weather of that place.

Question 3.
Who prepares the weather reports?
Answer:
The weather reports are prepared by the Materological Department of the Government. This department collects data on temperature, wind etc., and makes the weather prediction.

Question 4.
Define climate.
Answer:
The average weather pattern taken over a long time, say 25 years, is called the climate of the place.

Question 5.
Why do some places have hotter climate than others?
Answer:
The places nearer to the equator are usually hotter. This is because the sun’s rays are more concentrated near the equator than they are farther North or South.

Question 6.
Give two examples of animals found in cold climates.
Answer:
(i) Penguins
(ii) Polar bear.

Question 7.
Give two examples of animals found in hot and humid climate.
Answer:
(i) Red-eyed frog
(ii) Beard ape.

Question 8.
Name three desert animals.
Answer:
(i) Camel
(ii) Snake
(iii) Lizard.

Question 9.
Can a polar bear live happily on land?
Answer:
No, it lives where the land is fully covered with snow.

Question 10.
Where do the elephant live?
Answer:
Elephant lives in forest.

Question 11.
Where does penguin live?
Answer:
Penguin lives in very cold places.

Question 12.
Define adaptation.
Answer:
The particular features of an organism that makes it suited to a particular climate is called adaptation.

Question 13.
What do you understand by ‘summer sleep’?
Answer:
Animals like frog, crocodiles and alligators live in mud during the summer months. This is called the ‘summer sleep’.

Question 14.
What do you understand by hibernation?
Answer:
During winter, some animals like bears, bats, snakes, lizards, frogs and squirrels go to sleep. This is called the winter sleep or hibernation.

Question 15.
Where do the following animals live?
(i) Monkeys
(ii) Snakes
(iii) Rabbit
(iv) Fish.
Answer:
(i) On land and trees
(ii) On land and water
(iii) On land
(iv) In water.

Question 16.
Name three animals which are active during night;
Answer:
(i) Bat
(ii) Owl
(iii) Cockroach.

Question 17.
What is the difference between climate of Kashmir and Kerala?
Answer:
Kerala is very hot and wet in comparison to Kashmir, which has a moderately hot and moderately wet.

Question 18.
Name two countries where polar regions are found?
Answer:
(i) Canada
(ii) Sweden.

Question 19.
Name two countries where the tropical rainforests are found?
Answer:
(i) India
(ii) Malaysia.

Question 20.
Name a migratory bird.
Answer:
Siberian crane.

Short Answer Type Questions

Question 1.
Why do desert animals have thick skin?
Answer:
Animals living in hot places, such as snakes, desert rats and lizards are not able to get sufficient water. So these animals have a thick skin, which prevents evaporation. Since they do not sweat, they can survive| without water for a longer time.

Question 2.
How is camel adapted live in/ desert?
Answer:
Camel lives in desert. It has long legs which help it to lift its body above the ground. Thus camel is able to avoid direct contact with the hot ground. The camel drinks water 50 litre or above in one time and store it in its body. So it lives without water for longer time. Its skin is also thick which prevents transpiration of ‘ water. Thus camel is suited to live in desert.

Question 3.
How cold place animals protect themselves from cold?
Answer:
The animals which live in cold places like waives seals, and penguins have thick skin which protects them from cold. They also have thick ,fur.

Question 4.
How fishes are adapted to live in water?
Answer:
Fishes are best suited to live in water. They have boat like structure which help them in swimming in water. They have gills from which they get oxygen and food. The body of fishes contain different types of fins which help them from swimming in water. Fishes shape tapers which provide least resistance in swimming water.

Question 5.
Why do polar bears have white fur?
Answer:
Polars bears have white fur so that they are not easily visible in the snowy white background. It protects them from their predators. It also helps them in catching their prey. To protect them from extreme cold, they have two this layers of fur. They also live a er of fair under their skin.

Question 6.
Differentiate between weather and climate.
Answer:

Question 7.
Give some examples of sea water animals.
Answer:
Almost all types of animals live in sea water. Most of the sea water animals are actively swimming animals like fishes and whales. Animals like corals, star fish, and urchin live at the bottom of the sea.s

Question 8.
Write the factors which the climate of a region depend.
Answer:
The climate of a region depends on:
(i) The presence or absence of water (rainfall).
(ii) Amount of sunshine it gets.
(iii) The ability to transfer water to the atmosphere (evaporation), and
(iv) The place whether it is a hilly or a plain region.

Question 9.
Mention the adaptive features of the animals found n cold climates.
Answer:
The animals found in cold climates have a thick layer of fat under the skin. This gives them nourishment in winter. They also have thick coat of fur on their body which helps the stay warm. The examples of animals 6 in cold regions are reindeer, arctic fox, polar bear, etc.

Question 10.
Mention the adaptations in hot and dry climates.
Answer:
Animals living in hot and dry places usually have following adaptations:
(i) Short shiny fur to reflect the sun’s rays.
(ii) Keep the body cool through sweating and panting.
(iii) To avoid the strong sun, they feed in the morning or evening and hide behind rocks and in burrows during the day.
Examples: Camel, Ostrich and Snail.

Long Answer Type Questions

Question 1.
The Earth is the only planet on which life is exists, why? Explain.
Answer:
The Earth is not the only planet revolving around the Sun. There are eight other planets that revolve Ground tfye Sun. But Earth is the only planet on which life exists. A number of factors are responsible for it. These are:
(i) Distance of Earth from the Sun; this is sufficient to keep the temperature’ on the surface of Earth at an average of 30°C; life can exist at this temperature.
(ii) The layer of carboh dioxide and watervapour which surrounds Earth prevents too much heat from leaving Earth into space; otherwise the temperature of Earth would be -30°C.
(iii) The layer of Zone which surrounds Earth does not allow ultraviolet rays to reach Earth from the sun, other wise living onganisns will die.

Question 2.
Describe the adaptive features of camel.
Answer:
The camel is the animal that thrives on the best in such hpt climate. It is also called the ship of the desert. The camel is called so because of the following adaptations it has:
(i) Thick skin that prevents water loss through perspiration or evaporation.
(ii) Humps (one or two) present in the body. These are the storehouse of fat. The camel uses this fat when food is scarce.
(iii) Pouches in the body to store water. This enables the camei to go without water for many days.
(iv) Pads of skin under the feet that act like cushions and enable the camel to walk easily in the sand without sinking.
(v) Long curly eyelashes preventing the entry of sand into eyes and thick eyebrows to protect eyes from sun. The plants and animals living in cold regions also have certain features. These are different from those possessed by plants and animals living in hot regions.

Question 3.
Defind adaptation. Mention various adaptations in terrestrial animals.
Answer:
Climate influences living organisms directly. Hence, they develop certain traits that help them to thrive well in that particular climate. This is called adaptation.

The animals that live on land are called terrestrial animals. These animals have different types of habits and ways of living. The terrestrial animals may be runners (cursorial habit), burrowers and diggers (fossorial habit), climbers (scansorial or arboreal habit) and fliers (aerial habit). Accordingly, these animals have different types of adaptations, as described below.
A. Modification of foot: Terrestrial animals have different types of foot for locomotion.
(i) Pentadactily: Terrestial animals have pentadactyl (five digits) foo; bearing claws for walking and running. Pentadactyl foot are of following three types:
(а) Plantigrade: In this type of foot, the entire palm and sole rest on the ground e.g. bear, baboon, raccoon.
(b) Digitigrade: In this case, animals perform walking and running on the digits e.g. dogs, cat, hyaena.
(c) Unguligrade: In this case, animals perform walking and running on the tips of digits covered with modified nail called hoof. The distal toe bones (unguals) are depressed or flattened, e.g. pig, horse, donkey, rhinoceros.

(ii) Bipedality: Some terrestrial animals have two footed or bipedal mode of locomotion, which spares forelimbs for other types of jobs. e.g. human beings.

B. Modification of body and head:
(i) The fast moving animals like horse, dog, etc. have streamlined body to reduce the resistance offered by the air.
(ii) In burrowing and digging animals, the head and snout are tapering. e.g. snakes, shrew, mole.

C. Modification for respiration:
The majority of terrestrial animals are lung breathers. They have lungs for respiration, e.g. Frog, lizards, all mammals.

D. Protective adaptations:
Many terrestrial animals are able to modify their form, appearance, structure or behaviour to escape predation or to increase the chances of capturing the prey. For example frog can change its body colour to match the back ground.

Question 4.
Mention various adaptations in aquatic animals.
Answer:
A large number of animals live in aquatic habitat. They include both fresh water and marine (sea water) forms. Several invt ibrates such as prawn, Octopus, some insects are aquatic or semi aquatic. A number of vertebrates such as fishes, whales, dolphins are well adapted to aquatic mode of life. They have following adaptation for aquatic mode of life.
(i) Body contour: They have streamlined laterally compressed body to reduce friction. This allows swift passage in water while swimming.
(ii) Swimming organs: The fishes have fins and whales possess flippers which help them in swimming. Frogs and ducks have webbed feet for swimming.
(iii) Protective covering: The body of fishes is covered with scales and that of frog with a mucilaginous covering, which protect them from decaying effect of water.
(iv) Gills: Fishes have special breathing organs called gills, which use dissolved oxygen of water.
(v) Swim bladder or Air bladder:
Certain fishes (bony fishes) have swim bladder or air bladder. It is filled with air and maintain buoyancy.

Weather, Climate and Adaptations of Animals to Climate Class 7  HBSE Notes

1. The day-to-day condition of the atmosphere at a place with respect to the temperature, humidity, rainfall, wind-speed, etc.; is called the weather at that place.
2. The temperature, humidity and other factors are called the elements of the weather. The weather of a place charges day after day and week after week.
3. The maximum temperature of the day occurs generally in the afternoon while the minimum temperature occurs in the early morning.
4. The times of sunrise and sunset also change during the year.
5. All the changes in the weather are driven by the sun.
6. The average weather pattern taken over a long time, say 25 years, is called the climate of the place.
7. The tropical and the polar regions are the two regions of the earth, which have severe climate conditions. .
8. Animals are adapted to the conditions in which they live.
9. The polar regions are very cold throughout the year. The sun does not set for six months in a year and in the other six months it does not rise.
10. Animals in the polar region are adapted to the extremely cold climate by having some special characteristics such as white fur, strong sense of smell, a layer of fat under the skin, wide and large paws for swimming and walking etc.
11. Migration is another means to escape the harsh, cold conditions.
12. Because of the hospitable climatic conditions, huge populations of plants and animals are found in the tropical rainforests.
13. Animals in the tropical rainforests are adapted such that they eat different kinds of food to overcome the competition for food and shelter.
14. Some adaptations of animals living in the tropical rainforests include living on the trees, development of strong tails, long and large beaks, bright colours, sharp patterns, loud voice, diet of fruits, sensitive hearing, sharp eyesight, thick skin, ability to camouflage in order to protect themselves from predators etc.

Haryana State Board HBSE 7th Class Science Solutions Chapter 6 Physical and Chemical Changes Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 6 Physical and Chemical Changes

HBSE 7th Class Science Physical and Chemical Changes Textbook Questions and Answers

Question 1.
Classify the changes involved in the following processes as physical or chemical changes.
(a) Photosynthesis
(b) Dissolving sugar in water
(c) Burning of coal
(d) Melting of wax
(e) Beating aluminium to make aluminium foil
(f) Digestion of food.
Answer:
Physical Change (b), (d), (e)
Chemical Change (a), (c), (f)

Question 2.
State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook.
(a) Cutting a log of wood into pieces is a chemical change.
(b) Formation of manure from leaves is a physical change.
(c) Iron pipes coated with zinc do not get rusted easily.
(d) Iron and rust are the same substances.
(e) Condensation of steam is not a chemical change.
Answer:
(a) False
(b) False
(c) True
(d) True
(e) True.

Question 3.
Fill the blanks in the following statements:
(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of ………….. .
(b) The chemical name of baking soda is ……………… .
(c) Two methods by which rusting of iron can be prevented are …………. and …………. .
(d) Changes in which only …………. properties of a substance change are called physical changes.
(e) Changes in which new substances are formed are called …………. changes.
Answer:
(a) Calcium carbonate
(b) Sodium hydrogen carbonate
(c) Coating, galvanization
(d) Physical
(e) Chemical.

Question 4.
When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.
Answer:
When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas carbon dioxide.
lemon juice + baking soda → carbon dioxide + lime water
Since, a change in which one or more new substance are formed is called a chemical change, therefore this is a chemical change.

Question 5.
When a caùdie burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.
Answer:
Physical Change → Melting of ware
Chemical Change → Burning of candle

Question 6.
How would you show that setting of curd is a chemical change?
Answer:
The conversion of milk into curd, i.e., setting of curd is a permanent as well as irreversible and lead to the production of a new substance. The new substance, curd is formed has different composition and properties from the milk. Hence, setting of curd is a chemical change.

Question 7.
Explain why burning of wood is cutting it into small pieces are considered as two different types of a changes.
Answer:
Burning of wood is a chemical change because, in addition to new products burning is always accompanied by production of heat.
Cutting of wood into small pieces is a physical change because, pieces of wood underwent changes in size and no new substance is formed.

Question 8.
Describe how crystals of copper sulphate are prepared.
Answer:
Take a cup full of water in a beaker and add a few drops of dilute sulphuric acid. Heat the water. When it starts boiling add copper sulphate powder slowly while stirring continuously. Continue adding copper sulphate powder till no more powder can be dissolved. Filter the solution. Allow it to cool. Do not disturb the solution when it is cooling. Look at the solution after some time. Now, you can see the crystals of copper sulphate.

Question 9.
Explain how painting of an iron gate prevents it from rusting.
Answer:
The process of rusting can be represented by the following equation:
Iron (Fe) + Oxygen (O₂ from the air) + Water (H₂O) → rust (iron oxide Fe₂O₃).

For rusting the presence of both oxygen and water (or water vapour) is essential. In fact, if the content of moisture in air is high, which means if it is more humid, rusting becomes faster. So, prevent iron gate from coming in contact with oxygen, or water, or both. One simple way is to apply a coat of paint or grease. In fact, these coats should be applied regularly to prevent rusting.

Question 10.
Explain why rusting of iron objects is faster in coastal areas than in deserts.
Answer:
The water of coastal areas contain many salts. The salt water makes the process of rust formation faster. Thus, rusting of iron objects is faster in coastal areas than deserts.

Question 11.
The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder it exist as a liquid. When it comes out from the cylinder it becomes a gas (Change – A) then it burns (Change – B). The following statements pertain to these changes. Choose the correct one.
(i) Process – A is a chemical change
(ii) Process – B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change.
Answer:
(iii) Both process A and B are chemical changes.

Question 12.
Anaerobic bacteria digest animal waste and produce biogas (Change – A). The biogas is then burnt as fuel (Change – B). The following statements pertain to these changes. Choose the correct one.
(i) Process – A is a chemical change,
(ii) Process – B is a chemical change.
(iii) Both process A and B are chemical changes.
(iv) None of these processes is a chemical change.
Answer:
(iii) Both process A and B are chemical changes.

Extended Learning – Activities And Projects

Question 1.
Take three glass bottles with wide mouths. Label them A, B and C. Fill about half of bottle A with ordinary tap water. Fill bottle B with water which has been boiled for several minutes, to the same level as in A. In bottle C, take the same boiled water and of the same amount as in other bottles. In each bottle put a few similar iron nails so that they are completely under water. Add a teaspoonful of cooking oil of the water in bottle C so that it forms a film on its surface. Put the bottles away for a few days. Take out nails from each bottle and observe them. Explain your observations.
Answer:
Do yourself.

Question 2.
Prepare crystals of alum.
Answer:
Do yourself.

Question 3.
Collect information about the types of fuels used for cooking in your area. Discuss with your teachers/parents/others which fuels are less polluting and why.
Answer:
Do yourself.

HBSE 7th Class Science Physical and Chemical Changes Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is a physical change?
Answer:
Change in which no new product is formed.

Question 2.
What is a chemical change?
Answer:
A change in which a new substance with different properties is formed.

Question 3.
Which of the following substance contains only one kind of atoms?
copper, iron, iron sulphide, sulphur, oxygen gas, water, air and hydrogen gas.
Answer:
The following contains only one kind of atoms:
Copper, Iron, Sulphur, Oxygen gas, Hydrogen gas.

Question 4.
Which of the following substances are compounds and which are elements?
Magnesium oxide, Mercuric oxide, Carbon, Nitrogen, Potassium permagnate, Sodium carbonate.
Answer:
Elements: Carbon, nitrogen.
Compounds: Magnesium oxide, mercuric oxide, potassium permanganate, Sodium carbonate.

Question 5.
Write the symbol of the following elements:
Aluminium, calcium, chlorine, cobalt, iodine and mercury.
Answer:
Al, Ca, Cl, Co, I, Hg.

Question 6.
Ne is the symbol of neon. What else does it represent?
Answer:
This symbol represent one atom of Neon.

Question 7.
Which elements are represented by the following symbols?
Na, K, P, Pb, Ca, Zn, Br, Sn.
Answer:
Sodium, Potassium, Phosphorus, Calcium, Zinc, Bromine, Tin.

Question 8.
Name four Elements which occur in gaseous form.
Answer:
Oxygen, Nitrogen, Hydrogen and Argon.

Question 9.
When some one open a bottle of perfumes, you smell it from a distance why it is so?
Answer:
It is due to the property of gases that their molecules diffuse (move) easily in the air.

Question 10.
What is crystallisation?
Answer:
The process of separation of pure crystals of a substance from its hot and supersaturated (concentrated) solution on cooling is called
crystallisation.

Question 11.
Define chemical reaction.
Answer:
The process in which the originally present substances change into new substances is called a chemical reaction.

Question 12.
What is matter?
Answer:
Anything which occupies space and has weight is called matter. Example: Air, Water, Wood, Stone, etc.

Question 13.
What are solids?
Answer:
Any materials which has a definite shape and definite volume, at room temperature is called solid.

Question 14.
What are liquids?
Answer:
Any substance which has a definite volume but no definite shape and has one free surface is called liquids: Milk, Water, Fruit juice, Alcohol etc.

Question 15.
Name two elements that are abundantly found in air.
Answer:
The two elements that are found abundantly in air are Nitrogen element and Oxygen element.

Question 16.
Choose the elements from the following substances: Marble, Mercury, Air, Carbon.
Answer:
Mercury and Carbon are elements.

Question 17.
What is the difference between 2N and N?
Answer:
2N represent 2 atoms of nitrogen and N represent 1 molecule of nitrogen.

Question 18.
Which of the following contains only one kind of atoms?
Copper, Iron sulphide, Sulphur, Oxygen gas, Water, Air and Hydrogen gas.
Answer:
Copper, Iron, Sulphur, Oxygen gas, Hydrogen gas.

Question 19.
Which of the following substances are compounds and which are elements?
Magnesium oxide, nitrogen, potassium permanganate, sodium carbonate.
Answer:
Compounds: Magnesium oxide, Potassium permanganate, Sodium carbonate.
Elements: Nitrogen.

Question 20.
Write down the chemical symbols of the following elements: Potassium, Calcium, Phosphorus, Nitrogen, Sulphur.
Answer:
K, Ca, P₄, N and Sg.

Question 21.
Write the names of the elements having the following symbols: C, Br, P, Al, Si.
Answer:
Carbon, Bromine, Phosphorus, Aluminium and Silicon.

Question 22.
A given substance ‘X’ has definite shape, fixed volume, is in comprissible and non-diffusing. What is the physical state of the substance ‘X’?
Answer:
The substance ‘X’ is solid state.

Question 23.
Write the names of the elements which compose a molecule of water.
Answer:
Hydrogen and Oxygen.

Question 24.
Name the three most abundant elements on the earth’s crust.
Answer:
Iron, Aluminium and Silicon.

Question 25.
Give the chemical formulae of the following:
(i) Calcium hydroxide
(ii) Copper oxide
(iii) Iron chloride
(iv) Zinc nitrate
(v) Silver sulphate
(vi) Lead carbonate
(vii) Potassium phosphate
(viii) Sodium hydroxide
(ix) Hydrochloric acid
(x) Zince hydroxide.
Answer:
(i) Ca(OH)₂
(ii) CuO
(iii) FeCl₂
(iv) Zn (NO₃)₂
(v) Ag₂SO₄
(vi) PbCO₃
(vii) K₃PO₄
(viii) NaOH
(ix) HCl
(x) Zn(OH)₂.

Question 26.
Define reactents.
Answer:
The original substances that take part in a chemical reaction are called the reactants,

Question 27.
Define products.
Answer:
The substances that form as a result of chemical reaction are called the products.

Question 28.
Define chemical combination reaction.
Answer:
When two or more elements or compounds react chemically to form only one new product, then the reaction which takes place is called chemical combination.

Question 30.
Define chemical displacement reaction.
Answer:
When a more reactive element displaces a less reactive elements from its aqueous salt solution, the reaction which takes place is called chemical displacement.

Question 31.
What kind of chemical reaction takes place when a mixture of iron fillings are heated with sulphur?
Answer:
Chemical combination reaction.

Short Answer Type Questions

Question 1.
Formation of clouds is a physical change. Explain.
Answer:
Formation of clouds is a physical change. Clouds are formed by condensation of water vapours present in the atmosphere. When rainwater goes back on the earth no new product is formed. Therefore, it is a physical change.

Question 2.
Explosion of a cracker is a chemical change. Explain.
Answer:
When we burn a cracker, it exploide. Heat, light and smoke comes out after explosion. Many new products are formed. So, it is a chemical change.

Question 3.
Most physical changes are reversible. Give reasons with two examples.
Answer:
All physical changes are reversible. Because in physical changes, no new product is formed. They can be reversed easily.
Examples:
(i) Dissolving of sugar in water is a physical change and we get back sugar and water easily.
(ii) Formation of ice from water. In melting of ice, we can get water back.

Question 4.
Identify the type of change and state whether energy is evolved or absorbed in each one of the following:
Burning of a candle, lighting of a bulb, preparation of food by green plants, Volcanic eruption.
Answer:
(i) Burning of a candle: Chemical change, energy evolved.
(ii) Lighting of a bulb: Physical change, energy evolved.
(iii) Preparation of food by green plants: Chemical change, energy absorbed.
(iv) Volcanic eruption: Chemical change, energy evolved.

Question 5.
What is a chemical formula? What information does it provide?
Answer:
Chemical formula is a shorthand method of using symbols to represent the composition of a compound. Using it, we can get the following informations:
(i) Constituting name of the elements present in the compound, e.g., water has the formula H₂0. It shows that water is made up .. of two elements, hydrogen and oxygen.
(ii) Atoms present in each element, e.g.,
(iii) The composition of compound and the formula H₂O shows that in a molecule of molecular weight of the compound, this compound two atoms of hydrogen and one atom of oxygen are present.

Question 6.
What are the differences between chemical and physical changes?
Answer:
Differences between chemical and physical changes:

Question 7.
How is common salt obtained from sea water?
Answer:
In the coastal regions of India, especially in the Rann of Kutch in Gujarat and some parts of Tamil Nadu, the sea water is collected in shallow pits. It is then allowed to evaporate in the sun. As the water evaporates, the salt solution becomes supersaturated. This supersaturated solution cannot hold the excess salt. Thus, it separates out in form of salt crystals. These salt crystals are collected. They are redissolved in water and the solution is filtered to remove insoluble impurities. The clear solution is again evaporated so as to obtain the crystals of pure salt.

Question 8.
What is crystallisation? To what purpose is it put?
Answer:
The process of separation of pure crystals of a substance from its hot and supersaturated (concentrated) solution on cooling is called Crystallisation.

The process of crystallisation is employed for the separation of a pure water soluble substance from its mixture. For example, if there is a mixture of alum and common salt, the pure alum crystals can be separated by the process of crystallisation.

Question 9.
What is the significance of an equation?
Answer:
Significance of an equation:
(i) It tells us which substance reacted and which substances are produced.
(ii) It tells us the quantities of each of the reactants and each of the products.

Question 10.
Give four examples of a physical change.
Answer:
(i) Formation of dew.
(ii) Evaporation of water.
(iii) Melting of wax.
(iv) Making of ice-cream.

Question 11.
Give four examples of a chemical change.
Answer:
(i) Photosynthesis by plants.
(ii) Clotting of blood.
(iii) Curdling of milk.
(iv) Burning of candle.

Question 12.
State four characteristics of physical change.
Answer:
(i) It is temporary.
(ii) It is reversible.
(iii) No new substance is produced.
(iv) No change in the chemical properties.

Question 13.
State four characteristics of chemical change.
Answer:
(i) It is permanent.
(ii) It is irreversible.
(iii) New substance is produced.
(iv) Changes in the chemical properties due to the formation of new substances.

Question 14.
What happens when an iron blade of a knife is dipped in copper sulphate solution? What kind of chemical reaction takes place?
Answer:
When an iron blade of a knife is dipped in copper sulphate solution iron blade is coated with reddish deposit of copper. Thus, we can say that iron (more reactive element), displaces copper (less reactive element), from its aqueous copper sulphate solution. Chemical displacement reaction is takes place.

Question 15.
Why do the molecules in a liquid tend to stay together and give a condensed form?
Answer:
In a liquid, the molecular motion are not great enough to over come the force of attraction between molecules. That is why the molecules tend to stay together and give a condensed form.

Question 16.
On a hot summer day the cycle tubes burst suddenly. Explain why?
Answer:
The cycle tubes are filled with air. On a hot summer day, the temperature of the atmosphere is high. When cycle runs on the road, the friction between the cycle wheel and the path produces heat which raises the temperature of the air in the cycle tubes. On heating the air expands and exerts pressure in the inside of the tubes. Due to the pressure, the cycle burst suddenly on a hot summer day.

Question 17.
Why can the same substance exist in all the three states, that is, solid liquid and gas?
Answer:
The space between the molecules, the force of attraction between the molecules, and the amount of movement of the molecules of a substance can be changed by changing the pressure and temperature of the substance. So depending on the pressure and temperature, the same substance can exist in all the three states i.e., Solid, liquid and gaseous. For example under normal pressure water exists as a solid in the form of ice at a temperature of 0°C or below. It exists as a liquid in the form of water at the room temperature and as a gas in the form of steam at 100°C or above.

Question 18.
Write some important properties of an element.
Answer:
Properties of an element are:
(i) An element is made up of some kinds of atoms.
(ii) An element cannot be Broken up into much simpler substances,
(iii) An element can be represented by a chemical symbol.

Question 19.
What are the important characteristics of a compound?
Answer:
(i) Chemical compound is made up of two or more elements combined chemically.
(ii) They have fixed formula or composition.
(iii) They have fixed melting point (M.P.) and boiling point (B.P.).
(iv) Energy is either evolved or absorbed during formation of a compound.
(v) Properties of constituent elements are different from its compound, e.g., properties of water (H₂O) are different from properties of hydrogen and oxygen.

Question 20.
What does the formula CO₂ represent?
Answer:
Molecular formula CO₂ represents:
(i) the name of the compound carbon dioxide.
(ii) carbon dioxide is made up of two kinds of elements – carbon and oxygen.
(iii) one molecule of carbon dioxide has one atom of carbon and 2 atoms of oxygen.
(iv) the molecular mass of carbon dioxide is 12 + 2 x 16 = 44 gram.

Question 21.
How is salt obtained from sea-water?
Answer:
The seas are great sources of salts. A litre of a water contains about 35 grams of salts. Sodium chloride is the main salt. The sea-water is trapped in shallow called lagoons and is allowed to evaporate in sunlight to white solid crystal of salts. These crystals are processed and packed to send the markets.

Question 22.
Give three reasons for supporting that water is a compound and not a mixture.
Answer:
Water is considered a compound due to the following reasons:
(i) Water cannot be separated into its constituents, hydrogen and oxygen, by the physical process.
(ii) The properties of water are entirely different from those of its constituents hydrogen and oxygen.
(iii) Water contains hydrogen and oxygen combined together in a fixed proportions of 1:8 by weight.

Question 23.
Explain why solution of salt in water is considered a mixture and not a compound. Give three reasons.
Answer:
Salt solution is considered a mixture due to the following reasons:
(i) Salt solution can be separated into salt and water by the physical process.
(ii) Salt solution, shows the properties of both its constituents salt as well as water.
(iii) The composition of salt solution is variable i.e., the percentage of salt and water in different salt solutions are different.

Question 24.
What information do we get from a chemical equation?
Answer:
The informations obtained from a chemical equation are:
(i) Name of the substance (elements or compound) taking part in reaction, i.e., reactants and products.
(ii) The number of atoms and molecules of different substances.
(iii) The conditions under which the reaction takes place or taking part in reaction, for example:
N₂ + 3H₂ → 2NH₃
It represents 1 molecule of nitrogen combines with 3 molecules of hydrogen to form 2 molecules of ammonia.

Question 25.
“In a chemical reaction, there is only a rearrangement of the atoms of the reactants.” Explain this statement giving an example.
Answer:
In a chemical reaction, there is only a x’e. angement of the atoms of the reactants because when a chemical reaction occurs new products are formed. These products have same kind and number of atoms as are present in reactants. They are only rearrange to give new substances. For example, in a reaction between iron and sulphur to give iron sulphide the number of atoms of iron and sulphur are identical on both sides of the equation.
Fe + S → FeS (On heating)

Question 26.
What is done to make a chemical equation more informative?
Answer:
To make a chemical equation more informative it should be balanced and conditions of the reaction should be written above the arrow. For example,

It shows that 2 molecules of water on electrolysis break up into 2 molecules of hydrogen and 1 molecule of oxygen.

Question 27.
What do you understand by reactants and products?
Answer:
Reactants: Substances taking part in a reaction are called reactants. They are written on the left side of the chemical equation.
Products: Substances produced in a reaction are called products. They are written on the right side of the equation.
Example:

Long Answer Type Questions

Question 1.
What does a chemical formula represent?
Answer:
Significance of chemical formula:
(i) It represents the name of the substance.
(ii) It represents one molecule of the substance.
(iii) It gives the names of all the elements present in the molecule.
(iv) It represents the mass of one molecule.

As an example of the formula of H₂SO₄:
(i) Represents sulphuric acid.
(ii) Represent one molecule of sulphuric acid.
(iii) Tells that sulphuric acid contains three elements:
hydrogen, sulphur, and oxygen.
(iv) Tells that one molecule of sulphuric acid contains two atoms of hydrogen; 1 atom of sulphur and 4 atoms of oxygen.

Question 2.
What do you understand by the following terms? Give examples.
(i) Endothermic chemical change
(ii) Exothermic chemical change.
Answer:
(i) Endothermic chemical change: When a chemical change takes place with the absorption of heat energy, then the change is said to be endothermic. .
Examples: Heating of mercuric oxide to form mercury and oxygen. Heating of calcium carbonate to form calcium oxide and carbon dioxide.

(ii) Exothermic chemical change: When a chemical change takes place with the liberation of heat energy, the change is said to be exothermic.
Examples: Candle on burning liberates heat and light energy. Respiration is an exothermic change.

Question 3.
What is a compound? How does it differ from a mixture?
Answer:
A compound consists of two or more elements, joined together in a fixed ratio by chemical bonds. For example, water formed from hydrogen and oxygen, sodium chloride formed from sodium and chlorine, sugar formed from carbon, hydrogen and oxygen, nitre formed from potassium, nitrogen and oxygen are all compound.
Difference between compounds and mixtures:

Question 4.
What is the difference between a balanced and unbalanced chemical equations? Explain with an example.
Answer:
Difference between a balanced and unbalanced chemical equations:
In unbalanced chemical equations, the number of each element atoms do not same. As for example:
Mg + O₂ → MgO.
This is not a balanced equation because the number of Mg atom and oxygen atoms are not same on both the sides, Le., reactants and product sides. On the other hand, in a balanced chemical equation the number of each atoms of each elements on both sides should be equal. As for example:
2Mg + O₂ → 2MgO.
In this balanced chemical equation the number of magnesium atoms and oxygen atoms in the left hand side are equal to the right hand side of the equation. So it is a balanced chemical equations.
(i) A mixture consists of two or more chemically different substances.
(ii) The composition of mixture can be separated easily by simple means.
(iii) Its formation is not accompanied by absorption or evolution of heat, light or electricity.
(iv) Mixture do not have definite formula.
(v) Mixture do not have fixed M.P. and B.P.
(vi) Mixture can be homogeneous and heterogenous.

Question 5.
Balance the following equations:
(i) Fe + O₂ → Fe₂O₃
(ii) H₂O + H₂ → O₂
(iii) Mg + O₂ → MgO
(iv) Al + O₂ → Al₂O₃
(v) Fe + HCl → FeCl₃ + H₂
(vi) Cu + O₂ → CuO
(vii) Hg + O₂ → HgO
(viii) Zn + HCl → ZnCl₂ + H₂
(xi) Al + HCl → AlCl₃ + H₂
(x) N₂ + H₂ → NH₃
Answer:
(i) 4Fe + 3O₂ → 2Fe₂O₃
(ii) 2H₂O → 2H₂ + O₂
(iii) 2Mg + O₂ → 2MgO
(iv) 4Al + 3O₂ → 2Al₂O₃
(v) 2Fe + 6HCl → 2FeCl₃ + 3H₂
(vi) 2Cu + O₂ → 2CuO
(vii) 2Hg + O₂ → 2HgO
(viii) Zn + 2HCl → ZnCl₂ + H₂
(xi) 2Al + 6HCl → 2AlCl₃ + 3H₂
(x) N₂ + 3H₂ → 2NH₃

Physical and Chemical Changes Class 7  HBSE Notes

1. Properties such as shape, size, colour and state of a substance are called its physical properties.
2. A change in which a substance undergoes a change in its physical properties is called a physical change. A physical change generally reversible.
3. A change in which one or more new substances are formed is called a chemical change. A chemical change is also called a chemical reaction.
Some common examples of chemical change:
1. Burning of wood or charcoal.
2. Burning of Candle.
3. Decomposition of water into hydrogen and oxygen.
4. Formation of water from hydrogen and oxygen.
5. Digestion of food.
6. Curdling of milk.
7. Formation of biogas (Crobar gas).
8. Burning of petrol or diesel.
9. Smoking of cigarette.
10. Drying of paint.
11. Rusting of iron.
12. Ripening of fruit.
13. Baking of cake.
14. Photosynthesis by plants.
15. Formation of wine.

Some Common Examples of Physical Changes:
1. Formation of dew.
2. Evaporation of water.
3. Crystallisation of sugar from its solution.
4. Ringing of an electric bell.
5. Breaking of glass pane.
6. Making of ice-cream.
7. A rock rolling down a hill.
8. Bending of glass tube by heating.
9. Melting of wax.
10. Sublimation of camphor.

4. If you leave a piece of iron in the open for some time, it acquires a film of brownish substance. This substance is called rust and the process is called rusting.
5. Any pure substance which cannot be broken into two or more pure substances by any chemical means is called an element.
6. The smallest unit of an element, which takes part in a chemical reaction is called an atom.
7. The smallest unit of a pure substance, which always exists independently and can retain physical and chemical properties of that substance, is called a molecule.
8. A metal is an element which is generally malleable, ductile and a good conductor of heat and electricity. About 80% of the elements are metals.
9. Non-metals are bad conductors of heat and electricity. They are neither malleable nor ductile. Non-rr Hals are generally soft.
10. When the molecule of a substance contains two or more atoms of different elements, combined together in a definite ratio, then it is said to be a molecule of a compound.
Symbols of common elements (Metals)

11. When one or more substances (elements or compounds) undergo a chemical change, with the absorption or release of energy, so as to form one or more new products, then the change taking place collectively is called chemical combination.
12. When two or more elements or compounds react chemically to form only one new product, then the reaction which takes place is called chemical combination.
13. When a single chemical compound decomposes on heating or by some other kind of energy, so as to form two or more new substances (elements or compounds), then the chemical reaction which takes place is called chemical decomposition.
14. When a more reactive element displaces a less reactive element from its aqueous salt solution, the reaction which takes place is called chemical displacement.
15. When an acid solution reacts with a base or metal carbonate, so as to form a salt, then the reaction is called neutralisation reaction.
16. The process of separation of pure crystals of a substance from its hot and supersaturated (concentrated) solution on cooling is called crystallisation.

Haryana State Board HBSE 7th Class Science Solutions Chapter 13 Motion and Time Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 13 Motion and Time

HBSE 7th Class Science Motion and Time Textbook Questions and Answers

Question 1.
Classify the following as motion along a straight line, circular or oscillatory motion :
(i) Motion of your hands while running.
(ii) Motion of a horse pulling a cart on a straight road.
(iii) Motion of a child in a merry go round.
(iv) Motion of a child on a see-saw.
(v) Motion of the hammer of an electric bed.
(vi) Motion of a train on a straight bridge.
Answer:
(i) Oscillatory
(ii) along a straight, line
(iii) circular
(iv) oscillatory
(v) oscillatory
(vi) along a straight line.

Question 2.
Which of the following is not correct?
(i) The basic unit of time is second.
(ii) Every object moves with a constant speed.
(iii) Distance between two cities are measured in kilometres.
(iv) The time period of a given pendulum is not constant.
(v) The speed of a train is expressed in m/h.
Answer:
(ii), (iv) (v).

Question 3.
A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
Answer:
Time period of a pendulum is time taken to complete 1 oscillation
Time taken to complete = 32 s.
20 oscillations
Time taken to complete = \(\frac { 32 }{ 20 }\)s.
1 oscillation
= 1.6 s.
∴ Time period of pendulum is 1.6 seconds.

Question 4.
The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
Answer:
Distance = 240 km.
Time taken = 4 hr.
Speed = \(\frac { Distance covered }{time taken }\)
= \(\frac { 240 }{ 4 }\) \(\frac { km }{ h }\)
= 60 km/h.
Speed of the train is 60 km/h.

Question 5.
The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/ h also.
Answer:
Distance = 57336.0 km – 57321 km = 15 Km
Time = 8.50 Am. – 8.30 Aim. = 20 min
Speed = \(\frac { Distance }{ time }\) = \(\frac { 15 }{ 20 }\) km/m
= 0.75 km/m. = 45 km/h

Question 6.
Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/s. Calculate the distance between her house and’the school.
Answer:
Time taken = 15 min
Speed = 2 m/s.
Distance = Speed x time
= 15 x 2
= 30 m.
So, distance between Salma’s School and her house is 30 metre.

Question 7.
Show the shape of the distance-time graph for the motion in the following cases :
(i) A car moving with a constant speed.
(ii) A car parked on a side road.
Answer:

Question 8.
Which of the following relations is correct?
(i) Speed = Distance x Time
(ii) Speed = \(\frac { Distance }{ Time }\)
(iii) Speed = \(\frac { Time }{ Distance }\)
(iv) Speed = \(\frac { 1 }{ Distance x Time }\)
Answer:
(ii) Speed = \(\frac { Distance }{ Time }\) is correct.

Question 9.
The basic unit of speed is :
(i) km/min
(ii) m/min
(iii) km/h
(iv) m/s
Answer:
(iv) m/s

Question 10.
A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is :
(i) 100 km
(ii) 25 km
(iii) 15 km
(iv) 10 km
Answer:
(ii) 25 km

Question 11.
Suppose, the two photographs shown in Fig. 13.1 and Fig. 13.2, had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in these photographs. Calculate the speed of the blue car.
Answer:
0.1 cm/s or 10 m/s.

Question 12.
Fig. 13.16 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Answer:
‘A’ car is moving faster.

Question 13.
Which of the following distance-time graphs shows a truck moving with speed which is not constant?

Answer:

Extend Learning – Activities and Projects

Question 1.
You can make your own sundial and use it to mark the time of the day at your place. First of all find the latitude of your city with the help of an atlas. Cut out a triangular piece of a cardboard such that its one angle is equal to the latitude of your place and the angle opposite to it is a right angle. Fix this piece, called gnomon, vertically along a diameter of a circular board a shown in Fig. 13.4. One way to fix the gnomon could be to make a groove along a diameter on the circular board.

Next, select an open space, which receives sunlight for most of the day, Mark a line on the ground along the North-South direction. Place the sundial in the sun as shown in Fig. 13.4 Mark the position of the tip of the shadow of the gnomon on the circular board as early in the day as possible, say 8:00 AM. Mark the position of the tip of the shadow every hour throughout the day. Draw lines to connect each point marked by you with the centre of the base of the gnomon as shown in Fig. 13.4. Extend the lines on the circular board up to its periphery. You can use „ this sundial to read the time of the day at your place. Remember that the gnomon should always be placed in the North- South direction as shown in Fig. 13.4.

Answer:
Do it yourself.

Question 2.
Collect information about time-measuring devices that were used in the ancientitimes in different partrs of the world. Prepare a brief write up on each one of them. The write up may include the name of the device, the place of its origin, the period when it was used, the unit in which the time was measured by it and a drawing or a photograph of the device, if available.
Answer:
Do it yourself

Question 3.
Make a model of a sand clock which can measure a time interval of 2 minutes (Fig. 13.5).

Answer:
Do it yourself

Question 4.
You can perform an interesting activity when you visit a park to ride a swing. You will require a watch. Make the swing oscillate without anyone sitting on it. Find its time period in the same way as you did for the pendulum. Make sure that there are no jerks in the motion of the swing. Ask one of your friends to sit on the swing. Push it once and let it swing naturally. Again measure its time period. Repeat the activity with different persons sitting on the swing. Compare the time period of the swing measured in different cases. What conclusions do you draw from this activity?
Answer:
Do it yourself.

HBSE 7th Class Science Motion and Time Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is motion?
Answer:
Motion is the change in the position of a body with respect to time and its surroundings.

Question 2.
What is uniform motion?
Answer:
When a body covers equal distance in equal intervals of time, the motion is called uniform motion.

Question 3.
What is speed?
Answer:
Speed is the distance covered by a body in a unit time.

Question 4.
Write one way in which people used to measure time in early days?
Answer:
People used to measure time with the help of Sundials.

Question 5.
What is the use of stop-watch?
Answer:
Stop-watch is used to measure exact time in case of athletic events as it can be stopped and started any moment.

Question 6.
What is a pendulum?
Answer:
A pendulum is a small non-magnetic ball like body, suspended by a light string.

Question 7.
What is a uniform motion?
Answer:
Motion of a body along a straight line covering equal distances in equal intervals of time is called a uniform motion.

Question 8.
What are the units of measuring speed?
Answer:
Speed is measured in metre per second (m/s) or kilometre per hour (km/h).

Short Answer Type Questions

Question 1.
Distinguish between uniform and non-uniform motion.
Answer:
Uniform motion is the equal distances covered in equal intervals of time. It means body moves with a constant speed. Non-uniform motion is the unequal distances covered in equal intervals of time. It means the body moves with unconstant speed.

Question 2.
How can we make a pendulum of our own? What is the time period of a pendulum?
Answer:
We can make a pendulum by susptending a metal ball with a cotton thread. The other end of the thread can be tied to some support. The time taken by a pendulum to complete its to and fro movement i.e. one oscillation is called the time period of the pendulum.

Question 3.
How can we determine the motion made by any body to be uniform or non-uniform with the help of a distance – time graph?
Answer:
If the distance – time graph obtained shows a straight line, the motion of the body is said to be uniform and if we obtain a curved line on a distance time graph that means the body is undertaking non-uniform motion. Thus a distance time graph helps in determining the uniform or non-uniform speed of the body.

Question 4.
A train is running at a speed of 50 km/h. How long will it take to cover a distance of 250 km.?
Answer:
Speed = 50 km/h
Distance = 250 km.
Time = ?
S = \(\frac { d }{ t }\)
50 = \(\frac { 250 }{ t }\)
∴ t = \(\frac { 250 }{ 50 }\) hr = 5 hr.

Question 5.
Shatabdi Express takes 6 hours to reach Lucknow, at a speed of 60 km/h. Find the distance it travels.
Answer:
Time = 6 hr.
Speed = 60 km/h
Distance = Speed x time
= 60 x 6 = 360 km
∴ Shatabdi travels 360 km at a speed of 60 km/h in 6 hr.

Question 6.
A car travels a distance of 200 km at the speed of 50 km/h. Calculate the time taken to cover the distance.
Answer:
Distance = 200 km
Speed = 50 km/h
Time = \(\frac { Distance }{ Speed }\) = \(\frac { 200 }{ 50 }\) = 4h
Car will take 4 h to cover the distance.

Long Answer Type Questions

Question 1.
Given below is a table showing time taken by a car to travel various distances. What do you infer from this data?

Answer:
We see that the car covers the distance of first 10 m in 1 sec. It again covers the distance of 10 m in another time of 1 sec i.e. 2-1 = 1 sec. So, we find that the car covers every 10 m in each 1 sec. It means that the car is covering equal distance in equal interval of time. When a body covers equal distance in equal intervals of time, it is said to be in a uniform motion. So, this data shows that the car is moving with a constant speed.

Question 2.
Describe various methods used to measure time in earlier times?
Answer:
There were no electronic watches in earlier times. Measuring time was a little bid difficult. The earliest method of measuring time was based on the position of the Sun. The Sundials were used for this purpose. Time was measured by the shadow casted by the changing position of the Sun from day to night. Chinese made a water clock 6000 years ago. Sand Clock was also used to measure time. Sand Clock was used by Romans. The time taken by sand to fall into the lower chamber from the upper chamber was considered to be the unit of measuring time. The discovery of pendulum helped in determining the exact time before the electronic watches were invented.

Question 3.
What is a pendulum? How does it help in determing time?
Answer:
Pendulum is a simple device which shows periodic motion. A simple pendulum consists of a non-magnetic metal ball called bob. This bob is suspended with help of a string. The open end of the string is tied to a support. Bob of the pendulum is held at a side and released. It starts moving in a to and fro motion. This is called an oscillatory motion. The time taken by the pendulum to complete one oscillation is called time period. This time period is always same with a pendulum having same length. Time period changes with the change in the length of the string. The string of the pendulum is adjusted to the length, that it completes one oscillation in second and it keeps on moving the clock giving us time.

Motion and Time Class 7 HBSE Notes

• Motion is the change in the position of an object with respect to its surroundings.
• Motion can be of many types. It can be along a straight line, circular, oscillatory.
• Motion can be uniform or non-uniform motion.
• Uniform motion means equal distance covered in equal intervals of time. It means a constant motion.
• Non-uniform motion means unequal distance covered in equal intervals of time.
• Distance moved by an object in unit time is called its speed.
• Basic unit of measuring speed is (m/s) meter / second.
• Time is measured in respect to the periodic motions.
• Pendulum was the first device to measure time exactly.
• In earlier days time Was measured by various objects like sundials, sand clocks, water clocks, etc.
• With the discovery of pendulum, devices to measure exact time were invented.
• Now-a-days various devices like stop-watch and other electronic devices are used to measure time intervals smaller than even a second.
• Distance time graph gives us an idea about the motion of the object. Straight-line obtained on this graph depicts constant motion, while non-constant motion is depicted by various shapes on the graph.

Haryana State Board HBSE 7th Class Science Solutions Chapter 5 Acids, Bases and Salts Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 5 Acids, Bases and Salts

HBSE 7th Class Science Acids, Bases and Salts Textbook Questions and Answers

Question 1.
State differences between acids and bases.
Answer:

Question 2.
Ammonia is found is many household products, such as window cleaners. It turns red litmus blue, what is its nature?
Answer:
Basic.

Question 3.
Name the source from which litmus solution is obtained. What is the use of this solution?
Answer:
Litmus solution is extracted from lichens. It has a mauve (purple) colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue. It is available in the form of a solution, or in the form of strips of paper.

Question 4.
Is the distilled water acidic/basic/ neutral? How would you verify it?
Answer:
The distilled water is neutral. Put a drop of the distilled water on a strip of the red litmus paper with the help of a droper. We observe that colour of the litmus paper as not change.

The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. These substances are neither acidic nor basic.

Question 5.
Describe the proeess of neutralization with the help of an example.
Answer:
The process due to! which an acid completely reacts with a base to form salt and water as the only products is called neutralization.
Acid + Base → Salt + Water
Example: Hydrochloric add (HCl) + Sodium hydroxide (NaOH)
Sodium chloride (NaCl) + Water (H₂O)

Question 6.
Make “T” if the statement is true and ‘F’ if it is false.
(i) Nitric acid turn red litmus blue.
(ii) Sodium hydroxide turns blue litmus red.
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water.
(iv) Indicator is a substance which shows different colours in acidic and basic solutions.
(v) Tooth decay is caused by the presence of a base.
Answer:
(i) Flase
(ii) Flase
(iii) True
(iv) True
(v) True.

Question 7.
Dorji has a few bottles of soft drink in his restaurant. But unfortunately, these are not labelled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink; How will Dorji decide which drink is to be served to whom?
Answer:
Do yourself.

Question 8.
Explain why?
(a) An antacid tablet is taken when you suffer from acidity.
(b) Calamane solution is applied on the skin when an ant bites.
(c) Factory waste is neutralised before disposing it into the water bodies.
Answer:
(a) Our stomach contains hydrochloric acid. It help us to digest food. But too much of acid in the stomach causes indigestion. Sometimes indigestion is painful. To relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide. It neutralises the effect of excessive acid.

(b) The sting of an ant contains formic acid. When an ant bites, it injects the acidic liquid into the skin. The effect of the sting can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains Zinc carbonate.

(c) The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms. The factory wastes are, therefore, neutralised by adding basic substances.

Question 9.
Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you Identify them? You have only turmeric indicator.
Answer:
Do yourself.

Question 10.
Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
Answer:
The nature of the solution is neutral, because the solutions which do not change the colour of either red or blue litmus are known as neutral solution. These substances are neither acidic nor basic.

Question 11.
Consider the following statements:
(a) Acids and bases both change colour of all indicators.
(b) If an indicator gives a colour change with an acid, it does not give a change with a base.
(c) If an indicator changes colour with a base, it does not change colour with an acid.
(d) Change of colour in an acid and a base depends on the type of the indicator. Which of these statements are correct?
(i) All four
(ii) a and b
(iii) b and c
(iv) only d
Answer:
(ii) a and b.

Extended Learning – Activities And Projects

Question 1.
Using the knowledge of acids and bases, write a secret message with the help of baking soda and beet’root. Explain how it works.
(Hint: Prepare baking soda solution in water. Use this solution to write the message on a sheet of white paper with a cotton bud. Rub a slice of fresh beet root over the message.)
Answer:
Do yourself.

Question 2.
Prepare red cabbage juice by boiling a piece of red cabbage in water. Use it as an indicator and test the acidic and’ basic solutions with it. Present your observations in the form of a Table.
Answer:
Do yourself.

Question 3.
Bring the soil sample of your area, find out if it is acidic, basic or neutral. Discuss with farmers if they treat the soil in any manner.
Answer:
Do yourself.

Question 4.
Visit a doctor. Find out the medicines be prescribes to treat acidity. Ask him how acidity can be prevented.
Answer:
Do yourself.

HBSE 7th Class Science Acids, Bases and Salts Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is an acid Id
Answer:
A substance which dissolves in water to give hydrogen ions as the only positively charged ions’fs called an acid.

Question 2.
What are mineral acids? Give, three examples.
Answer:
The acids which are prepared from the minerals of the Earth are called mineral acids.
Examples: Sulphuric acid, Nitric acid, Hydrochloric acid.

Question 3.
What are organic acids? Give three examples.
Answer:
Organic acids are found in plant and animal products, for examples, oxalic acids, citric acid, acetic acid, etc.

Question 4.
A solution turns red litmus solution blue. Is the solution acidic or basic in nature?
Answer:
Basic.

Question 5.
Give two examples each of (i) Strong bases (ii) Weak bases.
Answer:
(i) Strong bases: Sodium hydroxide, potassium hydroxide.
(ii) Weak bases: Copper hydroxide, zinc hydroxide. .

Question 6.
What do you understand by the term “neutral substance?”
Answer:
The substances which do not bring about any change in the colour of common indicators are called neutral substances.

Question 7.
Name the acids present in:
(i) Vinegar
(ii) Lemon juice
Answer:
(i) Acetic acid (CH₃COOH)
(ii) Citric acid.

Question 8.
Write the names of three mineral acids.
Answer:
(i) Sulphuric acid (H₂SO₄)
(ii) Nitric acid (HNO₃) and
(iii)Hydrochloric acid (HCl) are mineral acids.

Question 9.
Which of the following are oxides?
H₂O, CO, Co, NO, CO₂ , NaOH
Answer:
Oxides: H₂O, CO, NO and CO₂.

Question 10.
From the following list select metallic oxide and non-metallic oxides: CaO, Fe₂O₃, N₂O₅, CO₂, Na₂O, SO₂.
Answer:
(i) Metallic oxide: CaO, Fe₂O₃ and Na₂O.
(ii) Non-metallic oxide: N₂O₅, CO₂ and SO₂.

Question 11.
What are indicators?
Answer:
The complex, naturally occurring substances, which change their colour on coming in contact with other substances are called indicators. Turmeric, litmus, china rose etc. are some indicators.

Question 12.
Name two neutral liquids.
Answer:
(i) Alcohol
(ii) Ether.

Question 13.
Name two neutral gases.
Answer:
(i) Hydrogen, (ii) Oxygen.

Question 14.
Name two neutral solids.
Answer:
(i) Common Salt
(ii) Sugar.

Question 15.
What do you understand by term concentrated acid?
Answer:
The acids which contain very little or no amount of water are called concentrated acids.

Question 16.
What are dilute acids?
Answer:
The acids which contain a large amount of water (or solutions of acids in water) are called dilute acids.

Question 17.
Name the kind of substance formed when an acid reacts with a base.
Answer:
Neutralised.

Question 18.
What is missing in the following equation?
Fat + ……. → Soap + Glycerol
Answer:
Fat + NaOH → Soap + Glyceral
Thus NaOH missing from the equation.

Question 19.
An element combines with oxygen to form an oxide. This oxide dissolves in water. This aqueous solution changes blue litmus to red. Write:
(i) The nature of element (metal or non-metal)
(ii) The general name of the oxide.
Answer:
(i) The element is non-metal.
(ii) General name of the oxide non-metallic oxide.

Question 20.
What happens when a non-metal oxide is dissolved in water?
Answer:
When a non-metal oxide is dissolved in water, it forms acids. Examples:
(i) CO₂ + HO₂ → H₂CO₃ (Carbonic acid).
(ii) SO₂ + HO₂ → H₂SO₃(Sulphuric acid).

Question 21.
State one characteristics, property of all acids.
Answer:
All acids contain replaceable hydrogen.

Question 22.
Name the gas obtained when a metal carbonate reacts with an acid.
Answer:
When a metal carbonate reacts with an acid, carbon dioxide gas is envolved. Example:

Question 23.
Write equations for the action of water on:
(i) MgO
(ii) Calcium oxide.
Answer:
(i) MgO + H₂O → Mg(OH)₂ (Magnesium hydroxide)
(ii) CaO + H₂O → Ca(OH)₂(Calcium hydroxide)

Question 24.
What are mineral acids? Give two examples.
Answer:
Mineral acids are those acids which are obtained from the earth. Examples, Sulphuric acid, Nitric acid.

Question 25.
Name the three salts which are commonly lised at home..
Answer:
Three, salts commonly used at home are:
(i) Sodium chloride
(ii)Sodium carbonate
(iii) Sodium hydrogen carbonate.

Question 26.
Give the chemical formula of slaked lime
Answer:
Chemical formula of slaked lime is Ca(OH)₂

Question 27.
Name one/compound of calcium which is used for bleaching cloth.
Answer:
Bleaching powder.

Question 28.
What is the formula of sulphuric acid?
Answer:
The formula of sulphuric acid is H₂SO₄.

Question 29.
A solution turns red litmus paper blue. What does this indicate about the chemical nature of the solution?
Answer:
The chemical nature of the solution is acidic.

Question 30.
What do you understand by anhydrous salt?
Answer:
Hydrated salts loose their water of crystallisation upon heating. They love their shape and colour also and becomes powered. They are called anhydrous salts.

Question 31.
Name two normal salts.
Answer:
(i) Sodium Chloride (NaCl)
(ii) Potassium nitrate (KNO₃).

Question 32.
Name two basic sdlts.
Answer:
(i) Calcium hydrdgen chloride [Ca(OH)Cl]
(ii) Magnesium hydroxy chloride [Mg(OH)Cl] etc.

Question 33.
Write the balanced chemical equations for the reaction that takes place when zinc, magnesium and sodium react with dilute hydrochloric acid.
Answer:
Reaction of hydrochloric acid (dil.) with Zn, Mg, and Na:
(i) Zn + 2HCl → ZnCl₂ + H₂
(ii) Mg + 2HCl → MgCl₂ + H₂
(iii) 2Na + 2HCl → 2NaCl + H₂

Question 34.
Write two uses of slaked lime.
Answer:
Uses of slaked lime:
(i) It is used in manufacture of bleaching powder.
(ii) It is used as an important building materials

Question 35.
Complete the following equations:
(i) CO₂ + H₂O → ……………..
(ii) CO₂ + 2Na0H → …………….. + ……………..
(iii) SO₂ + H₂O → ……………..
(iv) MgO + H₂SO₄ → …………….. + ……………..
(v) CaC0₃ + 2HCl → …………….. + ……………..
(vi) Na₂O + H₂O → ……………..
(vii) 2NaOH + H₂SO₄ → …………….. + ……………..
(viii) NaOH + HNO₃ → …………….. + ……………..
(ix) CaO + H₂SO₄ → …………….. + ……………..
(x) MgO + 2HCl → ……………..
Answer:
(i) CO₂ + H₂O → H₂CO₃ (carbonic acid)
(ii) CO₂ + 2Na0H → Na₂CO₃ + H₂O (sodium carbonate)
(iii) SO₂ + H₂O → H₂SO₃ (suiphurous acid)
(iv) MgO + H₂SO₄ → MgSO₄ + H₂O (magnesium sulphate)
(v) CaC0₃ + 2HCl → CaCl₂ + H₂O + CO₂ (Calcium Chloride)
(vi) Na₂O + H₂O → 2Na0H (sodium hydroxide)
(vii) 2NaOH + H₂SO₄ → Na₂SO₄ + H₂O (sodium suphate)
(viii) NaOH + HNO₃ → NaNO₃ + H₂O (sodiùm nitrate)
(ix) CaO + H₂SO₄ → CaSO₄ + H₂O (calcium sulphate)
(x) MgO + 2HCl → MgCl₂ +H₂O

Short Answer Type Questions

Question 1.
How can you test the presence of an acid in any substance?
Answer:
Acid can be tested in any substance by the following methods:
(i) Take a drop of the dilute solution of the substance on the tips of your tongue. If tastes sour, it is acidic.
(ii) Dip a blue litmus paper in the solution. If ‘ the colour of the litmus paper turns red, the solution is acidic.

Question 2.
What are organic acids? Give two examples.
Answer:
Soured milk, Lemon, Green mangoes and Karvanda are sour testing. All of them contain some naturally occuring acids. Such acids are also found in humans and plants materials. They are known as organic acids. The acids such as lactic acid, citric acid, tartaric acid and acetic acid are naturally occuring and known as organic acid.

Question 3.
What are the uses of mineral acids in industry?
Answer:
Use of’mineral acids in industry:
(i) Concentration sulphuric acid, nitric acid and hydrochloric acid are used in a large number of metallurgical operations, manufacture of fertilizers and preparations of large number of industrial chemicals.
(ii) Hydrochloric acid is used for removing the deposits from inside the boilers. This process is known as de-scaling.

Question 4.
What are indicators? Name two acid-base indicators.
Answer:
The substances which are used to identify whether a substance is an acid or base is called indicators. For example, litmus solutions give red colour with acids and blue colour with bases. Therefore, litmus is used as indicators. Substances which give different colours with acid and base are called acid-base indicators, for examples. Methyl orange, phenolphthalein.

Question 5.
What are acid salts? Give two examples.
Answer:
The salts which dissolves water to produce a solution, which behaves like an acid is called an acid salt.
Examples: Sodium hydrogen carbonate (NaHCO₃), Potassium hydorgen carbonate (KHCO₃), Sodium hydrogen sulphate etc.

Question 6.
How is potash alum prepared?
Answer:
A mixture of potassium sulphate and aluminium sulphate is dissolved in water and then the solution is concentrated. Potash alum is formed. It separates out as crystals.

Question 7.
Why are sodium bicarbonate and lemon juice used during indigestion?
Answer:
Sodium bicarbonate neutralizes the acidity in the stomach. Hence, it is used during indigestion. Lemon contains acid. It reacts with undigested food and softens it. Thus, lemon is also used in indigestion.

Question 8.
Why are brass vessels coated with tin or kalai?
Answer:
When brass vessels are used to cook food with tamarind or lemon juice, the acids present in it reacts with brass metal and corrode it. The kalai layer protects this vessels from the action of acids. Due to this reason brass vessels are coated with tin.

Question 9.
What is salt? Name any salts and give thier formulae.
Answer:
A substance formed by the neutralisation of an acid with a base is called salt.
Examples:
(i) Potassium nitrate (KNO₃)
(ii) Sodiun: nitrate (NaNO₃)
(iii) Calcium carbonate (CaCO₃)
(iv) Zinc sulphate (ZnSO₄)
(v) Copper sulphate (CuSO₄).

Question 10.
Define an acid. Give three properties of acids.
Answer:
An acid is a substance which when dissolved in water gives hydrogen ions. Examples: H₂SO₄, HNO₃ and HCl etc.
Properties of acids:
(i) They have a sour taste
(ii) They turn blue litmus solution red.
(iii) They have replaceable hydrogen ion.

Question 11.
What are bases? Mention three properties of alkalies.
Answer:
The substance which react with acids to form salt and water only are called bases. Examples: Cu(OH)₂, Fe(OH)₃, Pb(OH)₂ etc.
Properties of alkalies:
(i) They tarn red litmus paper blue
(ii) They have a better taste.
(iii) They turn methyl orange from pink to yellow.

Question 12.
What are the uses of sodium bicarbonate?
Answer:
Uses of sodium bicarbonate:
(i) It is used in medicines to neutralise the acidity in the stomach.
(ii) It is used as backing power.
(iii) It is used in fire extinguisher.

Question 13.
What are the uses of common salt?
Answer:
Uses of common salt:
(i) It is an essential constituents of our diet.
(ii) It is used in the manufacture of soap.
(iii) It is used for glazing pottery. .
(iv) It is a starting material for the manufacture of chlorine, hydrochloric acid, washing soda and sodium hydroxide.
(v) It is used as food preservatives.
(vi) It turns freezing mixture with ice.

Question 14.
Give five uses of potassium nitrate.
Answer:
Uses of potassium nitrate:
(i) It is used in the manufacture of gun powder.
(ii) It is used in making fire works.
(iii) It is used in refrigeration.
(iv) It is used as fertilizers.
(v) It is used in glass industry.

Question 15.
Which acids is called ‘the king of the acids’? Give its uses.
Answer:
Sulphuric acid (H₂SO₄) is called “the king of the acids”.
Uses of sulphuric acid:
(i) It is used in the manufacture of detergents.
(ii) It is used as a dehydrating agent.
(iii) It is used in storage batteries.
(iv) It is used in petrol refining.
(v) It is used in textile, paper and leather industry.
(vi) It is used in fertilizers industry for the manufacture of ammonium sulphate and superphosphate of lime.

Question 16.
Explain with the help of chemical equations how the following acids are formed?
Carbonic acids, Sulphurous acid, Phosphoric acid.
Answer:
(i) Carbonic acid is prepared by dissolving carbon dioxide in water.
CO₂ + H₂O → H₂CO₃ (Carbonic acid)

(ii) Sulphurous acid is formed by dissolving sulphur dioxide in water.
SO₂ + H₂O → H₂SO₃ (Sulphurous acid)

(iii) Phosphoric acid is prepared by dissolving phosphorus pentaoxide in hot water.
P₂O₅ + 3H20 → 2H₃PO₄ (Phosphoric acid)

Acids, Bases and Salts Class 7 HBSE Notes

1. Curd, lemon juice, orange juice and vinegar taste sour. These substances taste sour because they contain acids. The chemical nature of such substances is acidic. The word acid comes from the Latin word acere which means sour. The acids in these substances are natural acids.
2. A substance which produces hydrogen (H⁺) ions when dissolved in water is called an acid. This definition was given by Arrhenius, a Swedish Chemist in 1912.
3. The acids which are prepared from the minerals of the Earth are called mineral acids.
Examples of Mineral Acids

4. The acids which dissolve in water to give a large number of positively charged hydrogen ions are called strong acids.
Examples of Strong Acids : Sulphuric acid, nitric acid, hydrochloric acid and phosphoric acid are examples of strong acids.
5. The acids which dissolve in water to give a small number of positively charged hydrogen ions are called weak acids.
Examples of Weak Acids : Carbonic acid, acetic acid, sulphurous acid, formic acid, etc., are examples of weak acids. In fact, most of the organic acid are weak acids.
6. The acids which contain very little or no amount of water are called concentrated acids.
7. The acids which contain a large amount of water (or solutions of acids in water) are called dilute acids.
8. General Physical Properties of Acids
(i) They have a sour taste.
(ii) They turn blue litmus solution red.
(iii) They turn methyl orange solution pink.
(iv) They do not affect phenolphthalein solution.
(v) Strong acids have a corrosive action on skin. They cause painful blisters.
(vi) Most of the acids are soluble in water.
(vii) Acids solutions are conductors of electricity.
9. Uses of Acids

10. The substances which react with acids to form salt and water as only products are called bases. All oxides of metals are bases. All hydroxides of metals are bases.
11. All bases which are soluble in water are called alkalis.
12. Strong bases completely dissociate in aqueous solution. For example, sodium hydroxide (NaOH), potassium hydroxide (KOH), etc.
13. They undergo partial dissociation in aqueous solution. For example, copper hydroxide Cu(OH)₂, Zinc hydroxide Zn(OH)₂, etc.
14. The bases show the following properties:
(i) These have a bitter taste.
(ii) Bases neither have colour nor small. Only Ammonium hydroxide (NH₄OH) has a pungent smell.
(iii) The basic solutions are soapy to touch, i.e., if little amount of sodium hydroxide is rubbed on fingers, it would give a feeling as if soap has been applied on the fingers.
(iv) Bases turn red litmus blue.
(v) Bases contain hydroxide ions e.g., Sodium hydroxide is represented as NaOH, calcium hydroxide is represented as Ca(OH)₂, etc., where OH is the hydroxy group.
(vi) Bases react with acids to give salt and water.
15. Uses of Bases

16. Special type of substances are used to test whether a substance is acidic or basic. These substances are known as indicators. Turmeric, litmus, china, rose, petals (Gudhal), etc., are some of the naturally occurring indicators.
17. The reaction between an acid and a’base-is known as neutralisation. Salt and water are produced in this process with the evolution of heat.
Acid + Base → Salt + Water (Heat is evolved)
The following reaction is an example :
Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H₂O)

Haryana State Board HBSE 7th Class Science Solutions Chapter 14 Electric Current and its Effects Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 14 Electric Current and its Effects

HBSE 7th Class Science Electric Current and its Effects Textbook Questions and Answers

Question 1.
Draw in your notebook the symbols to represent the following components of electrical circuits: Connecting wires, Switch in the ‘OFF’ position. Bulb, Cell, Switch in the ‘ON’ position, and Battery.
Answer:
Draw in your notebook the symbols to represent the following components of electrical circuits :
Connecting wires — —
Switch in off position — —
Bulb — —
Cell — —
Switch in ‘on’ position — —
Battery — —

Question 2.
Draw the circuit diagram to represent the circuit shown in Fig. 14.1.
Answer:

Question 3.
Fig 14.2 shows four cells fixed on a board. Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.
Answer:

Question 4.
The bulb in the circuit shown in Fig 14.3 does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulbs glow.
Answer:
The problem in this circuit is that of the battery. The cells have not been arranged in right series. The correct circuit is like this.

Question 5.
Name any two effects of electric current.
Answer:
Electric current has following effects:

• Electric current can give rise to heating and lighting.
• Electric current can make a straight conductor a temporary magnet.

Question 6.
When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.
Answer:
When current is passed through the wire, it deflects the compass near it from its north-south position behaving like a magnet. This is called magnetic effect of the current. As we know that needle of the compass is made up of a thin magnet, when this needle comes in contact with another magnet the like poles of the magnet repell each other and opposite poles attract each other. So the deflection is seen in the needle. In this case the wire behaves like a magnet and cause deflection in needle of the compass.

Question 7.
Will the compass needle show deflection when the switch in the circuit shown by Fig. 14.4 is closed?

Answer:
No, because there is no source of electric current in this circuit i.e. there is no battery.

Question 8.
Fill in the blanks:
(a) Longer line in the symbol for a cell represents its _______ terminal.
(b) The combination of two or more cells is called a _______.
(c) When current is switched on in a room-heater, its _______.
(d) The safety device based on the heating effect of electric current is called a _______.
Answer:
(a) Positive
(b) Battery
(c) Element becomes red hot and emit heat
(d) Fuse.

Question 9.
Mark ‘T’ if the statement true and ‘F’ if it is false.
(a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell.
(b) When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks.
(c) An electromagnet does not attract a piece of iron.
(d) An electric bell has an electromagnet.
Answer:
(a) F
(b) T
(c) F
(d) T

Question 10.
Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.
Answer:
No, the plastic bags do not get attracted by the magnet, so they cannot be separated by an electromagnet. Plastic bags are not magnetic materials, only magnetic materials like iron can be attracted by the magnet.

Question 11.
An electrician is carrying out some repairs in your house. He wants to replace a fuse by a piece of a wire. Would you agree? Give reasons for your response.
Answer:
No, we would not agree to allow to replace the fuse by a wire. Wires in the fuses are of specific metting points. So we should always use ISI marked fuses in our houses to save short circuits.

Question 12.
Zubeda made an electric circuit using a cell holder shown in Fig. 14.4, a switch and a bulb. When she put the switch in the ‘ON’ position, the bulb did not glow. Help Zubeda in identifying the possible defects in the circuit.
Answer:
It is important to put the cells in right series. The positive terminal of the cell should be connected with negative terminal of the second cell. The switch should be closed properly and bulb should not be fused. If Zubeda will check these then the bulb will certainly glow.

Question 13.
In the circuit shown in Fig. 14.5
(i) Would any of the bulb glow when the switch is in the ‘OFF’ position?
(ii) What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?

Answer:
(i) No, bulb will glow.

(ii) The bulb A will glow first, follow by B bulb and then C, because A bulb comes first in the path of electric current flowing from positive terminal towards the negative terminal of the battery.

Extended Learning-Activities and Projects

Question 1.
Set up the circuit shown in Fig. 14.6 again. Move the key to ‘ON’ position and watch carefully in which direction the compass needle gets deflected. Switch ‘OFF’ the current. Now keeping rest of the circuit intact, reverse the connections at the terminal of the cell. Again switch ‘on’ the current. Note the direction in which the needle gets deflected. Think of an explanation.
Answer:
Do it yourself.

Question 2.
Make four electromagnets with 20, 40, 60 and 80 turns. Connect them one by one to a battery of 2 cells. Bring the electromagnet near a box of pins. Count the number of pins attracted by it. Compare the strengths of the electromagnets.
Answer:
Do it yourself.

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

Very Short Answer Type Questions

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

Question 2.
What is conventaional current?
Answer:
The current flowing the positive end of the conducting wire towards the negative end is called conventaional current.

Question 3.
What are the different sources of current in an electric circuit?
Answer:
Cell or a battery are the sources of elctric current in an electric circuit.

Question 4.
What role does a switch plays in an electric circuit?
Answer:
The switch regulates the flow of electric current. It allows the current to pass when it is in ‘ON’ position.

Question 5.
Write the symbols of the following : Switch (open).
Switch closed and a cell.
Answer:

Question 6.
What is an open electric circuit?
Answer:
An electric circuit having the switch in ‘off position is called open electric circuit.

Question 7.
What is a closed electric circuit?
Answer:
An electric circuit having the switch in ‘on’ position is called a closed circuit or a complete circuit.

Question 8.
Which effect of the electric current enables the room heater to heat the room?
Answer:
The heating and lighting effect of the electric current enables the room heater to heat the room.

Question 9.
What is a fuse?
Answer:
It is a safety device used to avoid damages from short circuits and over loading in electric appliances.

Question 10.
Which effect of the electric current is used in Electric bells?
Answer:
The magnetic effect of the electric current is used in electric bells to make the sound.

Short Answer Type Questions

Question 1.
What is an electric current and electric circuit?
Answer:
Flow of electrons is called electric current. The path through which the electric current passes is called an electric circuit.

Question 2.
What are the components of the electric circuit? Name different components of the electric circuit and draw their symbols.
Answer:
Various elelments connected in the electric circuit are called components of the electric circuit. Following are some components of electric circuit and their symbols :

Question 3.
What is a cell and what is a battery?
Answer:
Cell and battery are both the sources of electric current in an electric circuit. A cell has two terminals – +ve terminal and – ve terminal. A combination of two or more than two cells is called a battery. Battery is formed by joining a positive terminal of a cell to the negative terminal of other cell.

Question 4.
What is an electric fuse? Explain its working.
Answer:
A fuse is a safety device used in household circuit to prevent damage to electric appliances due to overload and short circuit. It is the weakest part in the electric circuit. It melts and breaks the circuits when the problem arises in the circuit due to short circuiting, overloading or fluctuations of current in power supply system.

Question 5.
What is short circuit and overloaded circuit?
Answer:
Short circuit occurs when live wire and neutral wire come in direct contact. The short circuit occurs either due to melting of plastic insulation or connection of live wire with the earth wire. An overload circuit is the one through which more current passes than it can bear.

Question 6.
What is an M. C. B.?
Answer:
M.C.B. is miniature circuit breaker. This is a safety device like a fuse. It is used instead of or in addition to fuses, in household circuits. It is a switch that automatically switches off a current when it exceeds the specified maximum limit.

Question 7.
Write any three applications of the electromagnets.
Answer:
Fallowing are the applications of the electromagnets :

• Electromagnets are used to separate scrap iron from other metallic scraps.
• Used in electric motors of washing machines, fans, air conditioners etc.
• Used for preparing strong magnets.

Long Answer Type Questions

Question 1.
Explain the construction and working of an electric bell with help of a labelled diagram.
Answer:
An electric bell consists of an electromagnet, Armature, contact spring, Hammer and gong.
Electromagnet: It consists of a U-shaped soft iron rod having insulated copper wire wounded on it. One end of wire is connected to terminal T and other to the brass stud.

Armature: is a soft iron rod, suspended to brass stud. It faces the poles of the electromagnet.

Contact spring is attached to the armature and to a silver-cadmium alloy contact point. Spring is made up of steel.

Contact screw adjustment: It is a brass pillar having a brass screw passing through it. The tip of the screw is made up of silver cadmium alloy. Pillar is connected to T₂ with a copper wire.

Hammer and Gong : Hammer is made up of steel and is attached to the armature. Gong is made up of brass, and the hammer strikes the gong to make the sound.

Working : When electric current passes through T₁ and T₂, current passes from the battery to electromagnet, then to the contact screw and to T₂ completing the circuit. Electromagnet pulls the armature towards itself, the contact spring gets under tension, hammer strikes against gong thus making the sound. The whole process stops, when current stops flowing.

Electric Current and its Effects Class 7 HBSE Notes

• Flow of electrons is called electric current.
• The path in which the electric current flows is called an electric circuit.
• Conventially the current is said to flow from positive end of the conducting wire to the negative end of the conducting wire.
• There are many components which are attached to the path of the electric current. These are called the elements of the electric circuit,
• Elements like cell, battery, switch, bulb, connecting wires are represented by different symbols.
• Cell and battery are the sources of the electric current in a circuit. Battery is the combination of two or more than two cells.
• A circuit is said to be complete or closed when the switch regulating the flow of the current is in ‘on’ position when the switch is in ‘off’ position the circuit is called open.
• Flow of the electric current causes certain effects like heating and lighting and electromagnetism.
• The electric appliances like room heaters, gysers, rods etc. give out heat due to heating effect.
• When electric current passes through a magnetic substance like iron, it behaves like a temporary magnet.
• Electric bell works on this principle.
• Hans Christian Oersted found out the relation between electricity and magnetism.
• A fuse is a safety device used in the household circuits to prevent damage to electric appliances due to overload or short circuits.

Haryana State Board HBSE 7th Class Science Solutions Chapter 15 Light Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 15 Light

HBSE 7th Class Science Light Textbook Questions and Answers

Question 1.
Fill in the blanks :
(a) An image that cannot be obtained on a screen is called _________.
(b) Image formed by a convex _________ is always virtual and smaller in size.
(c) An image formed by a _________ mirror is always of the same size as that of the object.
(d) An image which can be obtained on a screen is called a _________ image.
(e) An image formed by a concave _________ cannot be obtained on a screen.
Answer:
(a) virtual image
(b) mirror
(c) plane
(d) real
(e) lens.

Question 2.
Mark ‘T’ if the statement is true and ‘F’ if it is false :
(a) We can obtain an enlarged and erect image by a convex mirror.
(b) A concave lens always form a virtual image.
(c) We can obtain a real, enlarged and inverted image by a concave mirror.
(d) A real image cannot be obtained on a screen.
(e) A concave mirror always form a real image.
Answer:
(a) F
(b) T
(c) T
(d) F
(e) F

Question 3.
Match the items given in Column I with one Or more items of Column II.

Answer:
(a) (v)
(b) (ii)
(c) (i)
(d) (iii)
(e) (vi)

Question 4.
State the characteristics of the image formed by a plane mirror.
Answer:

• Plane mirror forms an erect image.
• It forms a virtual image.
• Size of the image is same as that of the object.
• Image gets formed at the same distance behind the mirror as the object stands infornt of it.
• Image formed is a laterally inverted image, i.e. right hand side of the object seems to be the left hand side and vice-versa.

Question 5.
Find out the letters of English alphabet or any other language known to you in which the image formed in a place mirror appears exactly like the letter itself. Discuss your findings.
Answer:
Letters like A, H, I, M, O, T, U, V, W etc appear same when seen through a plane mirror.

Question 6.
What is a virtual image? Give one situation where a virtual image is formed.
Answer:
The image which cannot be taken on a screen is called a virtual image. When some object is placed very close to the concave mirror we do not get any image of that object on the white screen placed behind the mirror. Such image is called a virtual image.

Question 7.
State two differences between a convex and a concave lens.
Answer:

Question 8.
Give one use each of a concave and a convex mirror.
Answer:

• Use of Concave mirror: Concave mirror is used by dentists to- examine the teeth.
• Use of Convex mirror: Convex mirror is used as side view mirror in vehicles.

Question 9.
Which type of mirror can form a real image?
Answer:
Concave mirror can form a real image.

Question 10.
Which type of lens forms always a virtual image?
Answer:
Convex lens always form a virtual image.

Choose the correct option in questions 11-13

Question 11.
A virtual image larger than the object can be produced by a _________.
(i) concave lens
(ii) concave mirror
(iii) convex mirror
(iv) plane mirror
Answer:
(iii) convex mirror

Question 12.
David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be _________.
(i) 3 m
(ii) 5 m
(iii) 6 m
(iv) 8 m
Answer:
(i) 3 m

Question 13.
The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear view mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be _________.
(i) 1m/s
(ii) 2m/s
(iii) 4mls
(iv) 8m/s
Answer:
(iii) 4mls

Extended Learning-Activities and Projects

Question 1.
Play with a mirror Write your name with a sketch pen on a thin sheet of paper, polythene or glass.

Read your name on the sheet while standing in front of a plane mirror. Now look at your image in the mirror.
Answer:
Do it yourself.

Question 2.
A burning candle in water
Take a shoe box, open on one side. Place a small lighted candle in it. Place a clear glass sheet (roughly 25 cm x 25 cm) infront of this candle (fig. 15.1). Try to locate the image of the candle behind the glass sheet. Place a glass of water as its position. Ask your friends to look at the image of the candle through the sheet of glass. Ensure that candle is not visible to your friends. Your friends will be surprised to see the candle burning in water. Try to explain the reason.
Answer:
Do it yourself.

Question 3.
Make a rainbow’.
Try to make your own rainbow. You can try this project in the morning of in the evening. Stand with your back towards the sun. Take a hosepipe or a water pipe used in the garden. Make a find spray in front of you. Your can see different colours of rainbow in the spray.
Answer:
Do it yourself.

Question 4.
Visit a laughing gallery in some science centre or a science park or a village mela. You will find some large mirrors there. You can see your distorted and funny images in these mirrors. Try to find out the kind of mirrors used there.
Answer:
Do it yourself.

Question 5.
Visit a nearby hospital. You can also visit the clinic of an ENT specialist, or a dentist. Request the doctor to show you the mirrors used for examining ear, nose,
throat and teeth. Can you recognise the kind of mirror used in these instruments?
Answer:
Do it yourseld.

Question 6.
Role play
Here is a game that a group of children can play. One child will be chosen to act as object and another will act as the image of the object. The object and the image will sit opposite to each other. The object will make movements, such as raising a hand, touching an ear, etc. The image will have to make the correct movement following the movement of the object. The rest of the group will watch the movements of the image. If the image fails to make the correct movement, she/he will be retired. Another child will take her/his place and the game will continue. A scoring scheme can be introduced. The group that scores the maximum will be declared the winner.
Answer:
Do it yourself.

HBSE 7th Class Science Light Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What do you mean by rectilinear propagation of light?
Answer:
Rectilinear propagation of light means that beam of a light always travels in a straight line.

Question 2.
How can we change the direction of the light?
Answer:
We can change the direction of the light by the phenomenon called reflection.

Question 3.
What do you mean by reflection of light?
Answer:
When a ray of light falls on the surface of any mirror, it bounces back in the same medium. This is called reflection of light.

Question 4.
What is a mirror?
Answer:
Any polished or shining surface is called a mirror.

Question 5.
What do you mean by a real image?
Answer:
Image which can be obtained on a screen is called a real image.

Question 6.
What do you mean by a virtual image?
Answer:
Image which cannot be obtained on a screen is called a virtual image.

Question 7.
What is a convex mirror?
Answer:
A mirror which reflects the light from its inner polished side.

Question 8.
What is a concave mirror?
Answer:
A mirror, which reflects light from its outer polished surface.

Question 9.
What kind of image is formed by a plane mirror?
Answer:
It forms an erect, virtual and image of same size as that of the object.

Question 10.
What kind of image is formed by a concave mirror?
Answer:
It can form both real and virtual, erect or inverted image.

Question 11.
What kind of image is formed when an object is placed very close to the concave mirror?
Answer:
A virtual erect and a magnified image will be formed.

Question 12.
What kind of image is formed by a convex mirror?
Answer:
Convex mirror forms an erect, virtual and diminished image.

Question 13.
What kind of image is formed by a concave lens?
Answer:
An erect, virtual and diminished image is formed by a concave lens.

Question 14.
What happens when a beam of light enters a prism?
Answer:
The beam of light splits into seven colours.

Question 15.
What do you mean by lateral inversion?
Answer:
When right hand side of an object appears as the left hand side and vice-versa.

Short Answer Type Questions

Question 1.
What is a virtual image? Give one example of virtual image.
Answer:
Virtual image : It is an image which cannot be obtained on a screen. It is formed when the reflected rays appears to meet each other but actually do not meet in reality. It is always erect. Image formed by a plane mirror is a virtual image.

Question 2.
What is real image of an object?
Answer:
Real image is formed when two or more reflected rays actually meet. This image can be obtained on a screen. It is always inverted. Pin-hole camera forms a real image.

Question 3.
Give two uses of concave mirror.
Answer:

• It is used as a reflector in search-light and head-lights of the automobiles.
• It is used as a shaving mirror.

Question 4.
Give two uses of convex mirror.
Answer:

• It is used in the cars and scooters to get the rear view to see the traffic coming from behind.
• It is used as reflectors in street lamps so as to diverse the light over a large area.

Question 5.
What do you mean by reflection of light?
Answer:
When a beam of light is incident on a plane surface a part of it is scattered back into the same medium. The scattering back of light into the same medium is called reflection.

Question 6.
Why is silvered glass used as a mirror?
Answer:
The silvered glass has a smooth surface and the smoothness helps in forming a clear image. Silvering makes it shiny and the shiny surface helps in reducing the absorption.

Question 7.
A man walks towards a plane mirror. At what rate will his image move if :
(a) the mirror is stationary,
(b) the mirror moves towards the man.
Answer:
(a) If the mirror is stationary the image moves at the same rate as the man.
(b) When the mirror moves towards the man the image moves at twice the rate of the mirror.

Question 8.
State four characteristics of the image formed by a plane mirror.
Answer:

• The image formed is as far behind the mirror as the object.
• It is exactly of same shape and size.
• It is erect but laterally inverted.
• It is virtual.

Question 9.
Distinguish between a real image and a virtual image.
Answer:
Difference between a real and virtual image :

Question 10.
Distinguish between a concave mirror and convex mirror.
Answer:

Long Answer Type Questions

Question 1.
How would you ascertain that a given mirror is a (a) Plane mirror, (b) Concave mirror, (c) Convex mirror without touching their surface?
Answer:
Hold the given mirror in the hand near your face, see the image. If the image is upright of the same size and does not change in size by moving the mirror, then the mirror is a plane mirror.

It the image is upright, larger and becomes inverted on moving the mirror away from your face, then the given mirror is a concave mirror. If the image is upright, smaller than your face and remains upright on moving the mirror away from your face, then the given mirror is the convex mirror. In this way one can ascertain the kind of mirror, without touching its surface.

Light Class 7 HBSE Notes

1. Light is an invisible energy which casue the sensation of sight.

2. Any object that gives out light is called the source of light e.g. Sun, firefly, candle etc.

3. Sun, moon, stars etc are called natural sources of light.

4. Candle, bulb etc are called man-made sources of light.

5. Light always travels in a straight line, this property of light is called the rectilinear propagation of light.

6. When light falls on a plane mirror, it falls back. This property of turning back of light is called in the same medium is called reflection of light.

7. There are two laws of reflection :
(i) The incident ray the normal at the point of incidence and the reflected ray lie in the same plane.
(ii) The angle of reflection is equal to the angle of incidence.

8. Any polished and shining surface is called a mirror.

9. Mirrors are of two types : concave mirror and convex mirror.

10. Concave mirror form a real and inverted image of the object.

11. Convex mirror always forms a virtual erect and small image.

12. Real image is one which can be obtained on a screen.

13. Virtual image is one, which cannot be obtained on a screen.

14. Lenses are also used to form images. Lenses are used to make spectacles, microscopes, magnifying glasses and telescopes etc.

15. Lenses are of two types. Concave lens and convex lens.

16. Concave lens is also called diverging lens, because it diverge the light falling on it. Convex lens is called the converging lens because it converges the light falling on it.

17. Concave lens forms, virtual erect and diminished image.

18. Convex lens can form both real and virtual images depending upon the position of the object. It magnifies the objects, when they are placed very near the lens.

19. White light splits into seven colours when it enters a prism.

20. This phenomenon is called dispersion of light.

Haryana State Board HBSE 7th Class Science Solutions Chapter 16 Water: A Precious Resource Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 16 Water: A Precious Resource

HBSE 7th Class Science Water: A Precious Resource Textbook Questions and Answers

Question 1.
Mark ‘T” if the statement is true and ‘F’ if it is false:
(a) The freshwater stored in the ground is much more than that present in the rivers and lakes of the world. (T/F)
(b) Water shortage is a problem faced only by people living in rural areas. (T/F)
(c) Water from rivers is the only source for irrigation in the fields. (T/F)
(d) Rain is the ultimate source of water. (T/F)
Answer:
(a) T, (b) F, (c) F, (d) T.

Question 2.
Explain How gropndwater is recharged?
Answer:
The ground water get recharged through the process of infiltration. Infiltration means seeping in water from rivers and lakes into the empty spaces and crack deep below the ground.

Question 3.
There are ten tubewells in a lane of fifty houses. What could be the long term impact on the water table?
Answer:
The effect on the water table depends on the replenishment of the underground water. As only five families will share a tubewell, the water used for daily domestic purpose will not effect the water table as such. But if there is acute shortage of rains the water used by the families will not replenished and water table will fall down.

Question 4.
You have been asked to maintain a garden. How will you minimise the use of water?
Answer:
The water is used to water the plants in a garden. To minimise the wastage of water we will use the technique of drip irrigation, which directly throws water at the base of plants. I will Check the leakages in the water papers. I will arrange small pits for rain water harvesting, The collected rain water will be used for watering loiter.

Question 5.
Explain the factors responsible for the depletion of water table.
Answer:
Various factors are responsible for the depletion of water table
(i) Increased Population : Increase in the human population has increased the demand for water. As the number of humans will keep on increasing, the consumption of water will also increase. Sources of water remain limited but consumption keeps on increasing causing great fall in, water table.

(ii) Increasing industries : All industries need water. Inlith increase in human population, the number of industries has also increased; so has increased the consumption of water mainly from ground. This has caused depletion of ground water.

(iii) Agricultural activities : India is a country whose economy depends on the agriculture. With time the land used for cultivation has increased. Therefore, the consumption of water for agricultural purpose has increased. Rains are the main source of water for irrigation. But irregular rain fall has increased the dependence of farmers on the ground water. This has increased the depletion of ground water.

(iv) Lack of water conservation techniques : Main source of/water on earth and for the underground water is the rain. The water of the rain, if conserved can increase the water level. But this is not done due to the lack of rain water harvesting techniques and other water conservation techniques.

Question 6.
Fill in the blanks with the appropriate answers :
(a) People obtain groundwater through _______ and _______ .
(b) Three forms of water are _______, _______ and _______ .
(c) The water bearing layer of the earth is _______.
(d) The process of water seewage into the ground is called _______.
Answer:
(a) wells and handpumps
(b) solid, liquid and vapour
(c) aquifer
(d) infiltration

Question 7.
Which one of the following is not responsible for water shortage?
(i) Rapid growth of industries.
(ii) Increasing population.
(iii) Heavy rainfall.
(iv) Mismanagement of water resources.
Answer:
(iii) Heavy rainfall.

Question 8.
Choose the correct option. The total water
(i) in the lakes and rivers of the world remains constant.
(ii) under the ground remains constant.
(iii) in the seas and oceans of the world remains constant.
(iv) of the world remain constant.
Answer:
(iii) in the seas and oceans of the world remains constant.

Question 9.
Make a sketch showing groundwater and water tube. Label it.
Answer:

Question 10.
Explain how ground water is recharged.
Answer:
The ground water get recharged through the process of infiltration. Infiltration means seeping in water from rivers and lakes into the empty spaces and crack deep below the ground.

Extended Learning-Activities and Projects

Question 1.
Role play
You are a water detective in your school. You have a team of six members. Survey the campus and make a note of the following:
(a) Total number of taps
(b) Number of taps leaking
(c) Amount of water wasted due to leakage
(d) Reasons of leakage
(e) Corrective measures taken
Answer:
Do it yourself.

Question 2.
Groundwater pumped out
Try to find out if there are any hand pumps in your neighbourhood. Go to the owner or the users of a few of these and find out the depth at which they struck water? If there are any differences, think of the probable reason. Write a brief report and discuss it in your class. If possible, visit a place where boring is going on to install a hand pump. Watch the process and find out the depth of the water table at that place. .
Answer:
Do it yourself.

Question 3.
Catching rainwater – Traditional methods
Form groups of 4 to 5 students in the class and prepare a report on the various traditional ways of water harvesting.
Answer:
Do it yourself.

Question 4.
Conservation of water
Carry out a compaign to conserve water at home and in the school. Design posters to remind others of the importance of water resources.
Answer:
Do it yourself.

Question 5.
Create a logo
Hold a competition to create a logo or a symbol depicting water scarcity.
Answer:
Do it yourself.

HBSE 7th Class Science Water: A Precious Resource Important Questions and Answers

Very Short Answer Type Questions

Question 1.
When do we celebrate water day?
Answer:
We celebrate water day on 22nd March every year.

Question 2.
How much minimum water is required by an individual for his daily requirements?
Answer:
According to survey of United Nations every individual require 50 litres of water every day.

Question 3.
What is the main source of water on the earth?
Answer:
Rain is the main source of water on the earth.

Question 4.
Name the main sources of the natural water.
Answer:
Main source of natural water on earth are two : Surface water and underground water.

Question 5.
What are the sources of surface water?
Answer:
Rain water, River and lake water and sea water are the three sources of surface water on earth.

Question 6.
What do you mean by underground water?
Answer:
Water from rain and other sources of surface water seeps inside the earth to fill the empty spaces and crack. It is called underground water.

Question 7.
What do you mean by infiltration?
Answer:
The process of seeping of water into the empty spaces of the ground is called infiltration.

Question 8.
What do you understand by aquifer?
Answer:
Aquifer is the underground water bearing layer of the earth, which is below the water table.

Question 9.
What are main sources of underground water?
Answer:
Main sources of underground water are springs, tubewells, wells, handpumps etc.

Question 10.
What is depletion of water table?
Answer:
Falling level of water at the water table is called depletion of water table.

Question 11.
Name the factors affecting the depletion of water table.
Answer:
Increase in human population, increasing industries and increasing agricultural activities are cause of depletion of water table.

Question 12.
What is water management?
Answer:
Minimum wastage of water is called water management.

Question 13.
What is drip irrigation?
Answer:
It is a technique using narrow tubings to water plants directly at their base without wasting water.

Question 14.
What symplasm in plants show scarcity of water?
Answer:
Wilting and drying.

Question 15.
How can we utilize the rain water?
Answer:
We can store rainwater with help of rain water harvesting techniques.

Short Answer Type Questions

Question 1.
What is the role of water in sustaining life on earth?
Answer:
Water is very important in sustaining life on earth. All the metabolic functions of living beings cannot be ‘performed without water. It provides habital to several animals and plants. So no living organism can survive without water.

Question 2.
What is surface water? What are its source?
Answer:
The water present on the surface of the earth is called the surface water. It can be obtained from rain water, water from rivers and lakes sea water contains maximum surface water.

Question 3.
What is underground water and how can it be obtained?
Answer:
A part of rain water gets percolated into the ground and collect to form a water table. This water is called underground water. Underground water can be obtained from springs, wells and tubewells. Handpumps are also means of obtaining underground water.

Question 4.
What is conservation of water? How can we conserve water.
Answer:
Conservation of water is the wise and fundicious use if, water by us. We can conserve water of harvesting rain water, minimising the wastage of water in houses and industries, using conservation techniques like drip irrigation in agriculture etc. can conserve our fresh water resources.

Question 5.
What do you mean by rainwater harvesting?
Answer:
Collecting and conserving the rain water from the roof tops of the buildings is called rain water harvesting. Water from the roof tops of the houses, industries etc. is collected. It is used directly or allowed to seep into the soil instead of allowing it to flow down. It helps in raising the water table.

Question 6.
What are water-wise habits?
Answer:
Following are the water-wise habits:

• brushing teeth shaving, etc with taps turned off while not using water.
• moking floor instead of washing.
• using small cisterns in toilets.
• using a bucket and mug to take bath instead of bathing under a shower.
• using harvested rain water.

Long Answer Type Questions

Question 1.
List main sources of water explaining each one briefly.
Answer:
There are mainly two sources of natural water.
(i) Surface water : The water which is present on the surface of earth is called the surface water.
It is of three types :

• Rain water : Rain water is the main source of water on the earth. It is the purest form of natural water.
• River and Lake water : The water is rivers and lakes came from rain and melting of snow.
• Sea water : Water from rivers, lakes and streams flow into the sea. Sea water cannot be consumed because it contains various soluble salts.

(ii) Underground Water : A part of rain water predates into the soil and gets collected there. It is called underground water. It can be obtained from the following :

• Spring Water : Some times the water that is collected above the rocks exert pressure. Consequently it comes out from any opening in the earth. It is called spring water.
• Well Water : Water collected inside the earth is called water table. Wells are dug to obtain water, borings are made to instal a hand pump or a tube well.

Question 2.
List the cause and effects of water scarcity.
Answer:
Cause of water scarcity : Following reasons cause the scarcity of fresh water on earth :
(а) Uneven Distribution of water :
There is uneven rainfall on the earth. Some places receive planty of rainfall while others do not receive any rain. Almost about half of the earths land area does not get sufficient rain.

(b) Lack of conservation facilities : Most of the rain water goes waste as it cannot be absorbed in the earth. It runs into other resources like sea, rivers etc. This water otherwise can be percolated into the soil and raise water table. Constructing small reservoirs, artificial lakes and other storage facilities can increase the water table.

(c) Pollution of water : Considerable amount of consignable water gets polluted due to human and industrial activities. This water if not polluted, can be consumed by human beings.

Effects following are the effects of water scarcity :

• acute shortage of water.
• drying up of pumps and lakes.
• failure of crops thus shortage of food.
• death of man and cattle.

Water: A Precious Resource Class 7 HBSE Notes

• Water is a vital natural resource.
• Main sources of natural water are surface water and underground water.
• Rain is the main source of water on the earth.
• Rainwater river and lake water and seawater are the sources of surface water.
• Springwater tubewells hand pumps are the means of obtaining under groundwater.
• level of water under the ground is called water table.
• Infiltration is the seeping of rainwater into the soil.
• Infiltration increases the water table.
• Excess usage of groundwater depletes the water table.
• Rainwater harvesting, drip irrigation etc. helps in conserving water.
• Increase in population, increase in industries, etc. Cause scarcity of water.
• Security of water can snatch away the greenry from the earth.

Haryana State Board HBSE 7th Class Science Solutions Chapter 17 Forests: Our Lifeline Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 17 Forests: Our Lifeline

HBSE 7th Class Science Forests: Our Lifeline Textbook Questions and Answers

Question 1.
Explain how animals dwelling in the forest help it grow and regenerate.
Answer:
Animals help in growing and regenerating forests in many ways. Animals work as the cleaning agents in the forest micro-organisms work on the dead bodies of plants and animals and degenerate them. This also renourishes the soil of the forest with the nutrients broken by the micro-organisms. Animals also help in dispersing the seeds of various plants and help in their pollination. This helps in growing a number of plants, which serve as a food for a number of herbivorous animals. Herbivores helps the carnivores to grow as they serve as food for them. Thus, the flora and fauna grows the in forests.

Question 2.
Explain how forest prevent floods.
Answer:
Forests can absorb a lot of water. The roots of the trees absorb the water and prevent it from flowing away. This helps in preventing floods.

Question 3.
What are decomposers? Name any two of them. What do they do in the forest?
Answer:
Decomposers are the organisms which feed on the dead bodies of the plants and animals. They clean the forests of the decaying dead bodies and replensish the nutrient back to the forest soil e.g. beetles and grubs.

Question 4.
Explain the role of forest in maintaining the balance between oxygen and carbon dioxide in the atmosphere.
Answer:
Plants release Oxygen in the atmosphere during the process called photosynthesis. This oxygen is inhaled by the animals living in the forest for their respirations. During respiration, they release carbon dioxide, which is absorbed by plants. In this way the O₂ – CO₂ cycle goes on in the forest.

Question 5.
Explain why there is no waste in a forest.
Answer:
There is no waste in the forest because decomposers convert all the dead bodies of the plants and animals into the humus. Humus gets added to the soil and no waste is remained.

Question 6.
List five products we get from forests?
Answer:
Products we get from forests:

• We get wood from forests which is used for many purposes like making furniture, paper etc.
• We get medicines from forest.
• We get fodder for our animals from forest.
• We get gum, wax etc.

Question 7.
Fill in the blanks :
(a) The insects, butterflies, honeybees and birds help flowering plants in __________.
(b) A forest is a purifier of __________ and __________.
(c) Herbs form the __________ layer in the forest.
(d) The decaying leaves and animals droppings in a forest enrich the __________.
Answer:
(a) pollination
(b) water and air
(c) lowest layer
(d) soil as humus.

Question 8.
Why should we worry about the conditions and issues related to forests far from us?
Answer:
We should be worried about deforestation, as it would lead to floods, increase in earth’s temperature, depriving animals of their habitats and soil erosion.

Question 9.
Explain why there is a need of variety of animals and plants in a forest.
Answer:
Animals and plants sustain the forest life CO₂ – O₂ cycle goes on in the forest due to animals and plants. Animals convert the dead plants and animals into humus and increase the fertility of soil. All food cycles and food webs need variety of plants and animals.

Question 10.
In Fig. the artist had forgotten to put the labels and directions on the arrows. Mark the directions on the arrows and label the diagram using the following labels :
clouds, rain, atmosphere, carbon dioxide, oxygen, plants, animals, soil, roots, water table.

Answer:
(See. Fig.)

Question 11.
Which of the following is not a forest product?
(i) Gum
(ii) Plywood
(iii) Sealing wax
(iv) Kerosene
Answer:
(iv) Kerosene

Question 12.
Which of the following statements is not correct?
(i) Forests protect the soil from erosion.
(ii) Plants and animals in a forest are not depedent on one another.
(iii) Forests influesce the climate and water cycle.
(iv) Soil helps forest to grow and regenerate.
Answer:
(ii) Plants and animals in a forest are not depedent on one another.

Question 13.
Micro-organisms act upon the dead plants to produce
(i) sand
(ii) mushrooms
(iii) humus
(iv) wood
Answer:
(iii) humus

Extended Learning-Activities and Projects

Question 1.
The Department of Environment is to decide whether some portion of a forest in your area could be cleared for a housing complex. Write a letter to the department explaining your point of view as a concerned citizen.
Answer:
Do it yourself.

Question 2.
Visit a forest. Here is a list of points that would make your visit more fruitful.
(а) Make sure that you have permission to go into the forest.
(b) Make sure that you can find your way around. Get a map and go along with some one who is familiar with the area.
(c) Keep a record of the things you see and do. Observations make the visit interesting. Sketches and photographs are useful.
(d) You may record bird calls.
(e) Collect different kinds of seeds or hard fruits like nuts.
(f) Try to recognise various types of trees, shrubs, herbs, etc. Make lists of plants from different places in the forest and of diferent layers. You may . not be able to name all the plants, but it is worth recording and seeing where they grow. Make a record of approximate heights of plants, crown shape, bark texture, lea size, and flower colour.
(g) Learn to recognise the animal’s droppings.
(h) Interview the forest officials and the people of surrounding villages and other visitors.
Answer:
Do it yourself.

HBSE 7th Class Science Forests: Our Lifeline Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Write three things we get from forests.
Answer:
Wood, gum and medicine

Question 2.
What is a forest?
Answer:
Forest is a place hosting a number of plants and animals.

Question 3.
Which plants constitute canopy in forests?
Answer:
Tall and giant trees.

Question 4.
Which plants constitute the understoreys in forest?
Answer:
Shrubs, tall grasses and small trees.

Question 5.
What is the basic unit of any food chain?
Answer:
Plants.

Question 6.
Draw any simple food chain going on in the forest.
Answer:
Grass → insects → frog snake → eagle.

Question 7.
What is Humus?
Answer:
Humus is a dark coloured substance which is formed from the dead bodies of plants and animals.

Question 8.
What are decomposers?
Answer:
The micro-organisms which decompose the dead bodies of the plants and animals are called decomposers.

Question 9.
Who helps in the dispersal of seeds of plants in the forest?
Answer:
Animals and wind helps in dispersal of seed.

Question 10.
How does forest help in preventing floods?
Answer:
Forests absorb the rain water in the soil and prevent the floods.

Question 11.
Why the noise pollution is less in the areas situated near the forests?
Answer:
Forest absorb the noise and prevent noise pollution.

Question 12.
What is deforestation?
Answer:
Cutting and destroying the forest is called deforestation.

Question 13.
What are the effects of deforestation?
Answer:
Floods, rising temperature, scarcity of food and wood and disturbed food chains are the results of deforestation.

Question 14.
How can we preserve our forest wealth?
Answer:
We can preserve our forest wealth by planting more and more trees.

Question 15.
What do you mean by afforestation?
Answer:
Planting more trees is called afforestation.

Short Answer Type Questions

Question 1.
Write any four products we get from forests.
Answer:

• We get wood from the forests.
• We get medicinal plants from the forests.
• We get gum and paper from the forests.
• We get food from forests in form of plants and animals.

Question 2.
What kind of flora is found in the forest?
Answer:
We can find wide variety of plants in the forest. We can find huge and giant trees. We can find small trees and shrubs. Various small plants like shrubs and grasses are also found in the forest.

Question 3.
What is a food chain?
Answer:
All the living components of the forest depend upon each other for their food. This interdependence of one organism on other for food is called a food chain.

Question 4.
What do you mean by micro-organisms?
Answer:
Micro-organisms as the name suggest are very small organisms. These organisms are so small that they cannot be seen with naked eyes. They can be seen under a microscope only e.gt bacteria, yeast etc.

Question 5.
What are decomposers?
Answer:
Decomposers are the micro-organisms which feed on the dead bodies of the plants and animals. They convert the dead bodies of these plants and animals into fertile humus.

Question 6.
How forests help in bringing rain?
Answer:
Trees absorbs water from the soil through their roots. They then release the excess of water through the process of transpiration in the form of water vapours. These water vapours form clouds and clouds bring rain.

Long Answer Type Questions

Question 1.
List the utility of forests.
Answer:
Forests are indispensible for us. They play an important role in our lives and in our environment.
Following are the importance of the forests:
(i) Forests give us a number of products which are very useful for us. They provide us wood. Wood is used to make furniture, house, toys, sports and fuel. Forests give us many medicinal plants. They give us gum, wax, catechu fruits, fodder and many more things.

(ii) Forests help in causing rains.

(iii) Forests maintain the temperature of the earth.

(iv) Forests maintain the O₂ – CO₂ cycle going on in the environment.

(v) Forests maintain the water-cycle going on in the environment.

(vi) Forests prevent many climate disaters like flood and draughts.

(vii) Forest provide shelter to a lot of wild life.

Question 2.
How forest sustain various variety of animals?
Answer:
Forests have different types of animals in it. Herbivores, Carnivores and Scvengers etc. Forest provide all the conditions necessary for their living. They get their food in the forest itself. The herbivores get their food in the form of plants. Carnivores eat the herbivores and systain their lives. Scavengers live on the dead bodies of all these animals and plants. Various invisible micro-organisms also live in forest. These micro-organisms are called decomposers. They convert the dead remains of animals and plants into the fertile humus.

Question 3.
What is the importance of scavengers and decomposers in the forests?
Answer:
A number of animals and plants live in forests. When they die, no body cremate their dead bodies. They keep on lying there. Scavengers like vultures, eagles etc. eat their dead bodies. They eat the flesh and other soft orgAnswer: The rest of the dead bodies are broken down by various micro-organisms called decomposers. They decompose the dead bodies of animals and plants into a dark substance called humus which is very nutritious for the soil. If scavengers and decomposers do not eat the dead bodies of animals and plants, the forest would become a big store of dead bodies and unfit for any wild life. This would disturb the whole environmental balance.

Forests: Our Lifeline Class 7 HBSE Notes

• A major part of our land is covered with forest.
• Forests are very important renewable resource.
• Forest help in maintaining the CO₂-O₂ cycle in our environment.
• They serve as a habitat to a number of plants and animals.
• Forests are indispensible for human life.
• A lot of variety of small and big plants can be found in forests.
• Different species of animals and birds live in the forest.
• All the biotic and abiotic components of the forest are interrelated with each other.
• All these components serve as complementary to each other.
• Forests save the soil erosion and maintain the water table beneath the soil.
• They cause the rains and maintain the water cycle.

Haryana State Board HBSE 7th Class Science Solutions Chapter 4 Heat Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 4 Heat

HBSE 7th Class Science Heat Textbook Questions and Answers

Question 1.
State similarities and differences between the laboratory thermometer and the clinical thermometer.
Answer:
Laboratory Thermometer: While performing experiments involving the measurement of temperature in the laboratory, a mercury thermometer is used. It is a thermometer having graduations marked on the Celsius scale from 0°C to 100°C.

The difference between the lower and upper fixed points is called range of the thermometer. The range of a mercury thermometer is 100°C. A mercury thermometer having graduations from 0°C to 100°C is shown in figure 4.8.

Clinical Thermometer:
To measure the temperature of a person running fever, doctor uses a thermometer known as Clinicdl Thermometer. It is a specially designed mercury thermometer and is used in the clinics and hospitals by doctors to measure human body temperature.

In construction, it differs from laboratory thermometers, in the sense that a kink or constriction is provided in the stem just above the bulb. Because of this kink, mercury doesn’t fall back into the bulb when clinical thermometer is taken out of the mouth of a patient to know the temperature. A jerk is given to the thermometer so that it is set again for measuring human body temperature. The temperature interval marked on the clinical thermometers ranges from 35°C to 43°C.

Question 2.
Give two examples each of conductors and insulators of heat.
Answer:
Conductors: aluminium, iron
Insulators: plastic, wood

Question 3.
Fill in the blanks:
(a) The hotness of an object is, is determined by its …………… .
(b) Temperature of boiling water cannot be measured by a …………… thermometer.
(c) Temperature is measured in degree ……………. .
(d) No medium is required for transfer of heat by the process of ………….. .
(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of …………. .
(f) Clothes of …………… colours absorb heat better than clothes of light colours.
Answer:
(a) Touching
(b) Clinical
(c) Celsius
(d) Radiation
(e) Conduction
(f) Dark

Question 4.
Match the following:

Answer:

Question 5.
Discuss why wearing more layers of clothing of during winter keeps us warmer tljian wearing just one thick piece of clothing?
Answer:
More layers of clothing keep us warm in winters as they have a lot of space between them. This space gets filled up with air. As air is a bad conductor, it does not allow the body heat to escape out.

Question 6.
Look at Fig. 4.10. Mark where the heat is being transferred by conduction, by convection and by radiation.
Answer:

Question 7.
In places of hot climate it is advised that the outer walls of houses be painted white. Explain.
Answer:
In places of hot climate it is advised that the outer wail of houses be painted white because white colour do not radiate heat easily.

Question 8.
One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will he:
(a) 80°C
(b) More than 50°C but less than 80°C
(d) 20°C
(d) Between 30°C and 50°C
Answer:
(b) More than 50°C but less than 80°C

Question 9.
An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will:
(a) Flows from iron ball to water.
(b) Not flow from iron ball to water or from water to iron ball.
(c) Flows from water to iron ball.
(d) Increase the temperature of both.
Answer:
(a) flows from iron ball to water.

Question 10.
A wooden spoon is dipped in a cup of ice-cream. Its other end:
(a) Becomes cold by the process of conduction.
(b) Becomes cold by the process of convection.
(c) Becomes cold by the process of radiation.
(d) Does not become cold.
Answer:
(d) does not become cold.

Question 11.
Stainless steel pans are usually provided with copper bottoms. The reason for this could be that:
(a) Copper bottom makes the pan more durable.
(b) Such pans appear colourful.
(c) Copper is a better conductor of heat than the stainless steel.
(d) Copper is easier to clean than the stainless steel.
Answer:
(c) Copper is a better conductor of heat than the stainless steel.

Extended Learning – Activities And Projects

Question 1.
Go to a doctor or your nearest health centre. Observe the doctor taking temperature of patients. Enquire:
(a) Why he/she dips the thermometer in a liquid before use.
(b) Why the thermometer is kept under the tongue.
(c) Whether the body temperature can be measured by keeping the thermometer at some place other than mouth.
(d) Whether the temperature of different parts of the body is the same or different. You can add m.ore questions which come to your mind.
Answer:
Do yourself. You can take help of your family doctor.

Question 2.
Go to a veterinary doctor (a doctor who treats animals). Discuss and find out the normal temperature of domestic animals and birds.
Answer:
Do yourself.

Question 3.
Wrap a thin paper strip tightly around an iron rod. Try to burn the paper with candle while rotating the iron rod continuously. Does it burn? Explain your observation.
Answer:
Do yourself.

Question 4.
Take two similar transparent glass bottles having wide mouths. Put a few crystals of potassium permaganate or pour a few drops of ink in one bottle. Fill this bottle with hot water. Fill the other bottle with cold water. Cover the cold water bottle with a thick piece of paper such as a postcard. Press the postard firmly with one hand and hold the bottle with the other hand. Invert the bottle and place it on top of the hot water bottle. Hold both the bottles firmly. Ask some other person to pull the postcard. Observe what happens. Explain.
Answer:
Do yourself.

HBSE 7th Class Science Heat Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is heat?
Answer:
The energy transferred from one body to another body due to a temperature difference between them is called heat.

Question 2.
Define temperature.
Answer:
Temperature is the degree of hotness or coldness of a body.

Question 3.
Define thermometer.
Answer:
A device used for measuring the temperature of different objects is called a thermometer.

Question 4.
Hot water bottles are used for fermentations. Explain why?
Answer:
Hot water bottles are used for fermentation as the water does not cool quickly due to its large specific heat capacity.

Question 5.
When equal amount of air, iron and oil are heated from 15°C to 25°C. List them in the order of increasing expansion.
Answer:
Iron, oil, air.

Question 6.
Name any four substances which expand on heating.
Answer:
Aluminium, steel, iron and copper.

Question 7.
Name any two substances which have negligible changes in length on heating.
Answer:
Pyrex glass, Invar.

Question 8.
Name two substances which contract on heating?
Answer:
Ice, Bismuth.

Question 9.
Do all liquids expand when heated or is there any exception?
Answer:
Yes, below 4°C when heated, water contract in stead of expanding.

Question 10.
Which substances has the highest heat capacity?
Answer:
Water.

Question 11.
What is the temperature of a normal human being on the Celsius scale?
Answer:
The temperature of a normal human being on the Celsius scale is 37°C.

Question 12.
Name the thermometer used for measuring the temperature of the human body.
Answer:
The thermometer used to measure the temperature of a human body is called clinical thermometer.

Question 13.
Define convection.
Answer:
The phenomenon due to which particles of a medium actually move to the source of heat energy and then move away from it after absorbing heat energy is called convection.

Question 14.
Why is convection not possible in solids?
Answer:
The molecules of a solid are held strongly due to intermolecular forces. As these molecules cannot travel to the source of heat energy, convection is not possible in case of solids.

Question 15.
What is ventilation?
Answer:
The process by which impure and warm air inside a room is continuously replaced by fresh air from outside is called ventilation.

Question 16.
What do you understand from the term lower standard point?
Answer:
The 0°C correspondence to the temperature of pure melting ice and is called the lower standard point.

Question 17.
What do you understand by upper standard point?
Answer:
100°C corresponds to the temperature of pure boiling water and is called the upper standard point.

Question 18.
Define conduction.
Answer:
The process of transmission of heat energy in solids without the actual movement of particles from their position is called conduction.

Question 19.
Give two examples to show that heat caused biological changes.
Answer:
(i) Conversion of ‘gur’ into alcohol.
(ii) Conversion of milk into curd.

Question 20.
Why is ice wrapped in gunny bags?
Answer:
Gunny bags have a number of fine pores, filled with air. Air being a bad conductor of heat does not allow the external heat to go in and melts the ice.

Question 21.
Why is tea generally served in China clay cups and plates?
Answer:
Because the China clay is bad conductor of heat and checks the heat conduction from the tea to the surroundings and thus keeps the tea hot.

Question 22.
By which of the processes (conduction, convection, radiation), it is not possible to transfer heat?
(i) In a vacuum
(ii) Through the solid material.
Answer:
(i) Conduction and convection
(ii) Convection and radiations.

Question 23.
Why do we use cooking utensils made of metals and alloys?
Answer:
Metals and alloys are good conductors of heat so that the heat from the flame is conducted to the food inside quickly and efficiently.

Question 24.
Is medium necessary for the transference of heat by radiations?
Answer:
No, medium is not necessary for the transference of heat by radiation.

Question 25.
Why do we feel warm while standing beside a burning furnace?
Answer:
When we stand beside a burning furnace, we feel warms, because of the heat radiation coming from the furnace.

Question 26.
Firemen wear helmets made from brass polished from outside. Why?
Answer:
Brass polished helmets reflects most of the heat and absorbs only a very little part of it when they fight against a fire.

Question 27.
When does the conduction of heat stop in two bodies in contact?
Answer:
The conduction of heat stops in two bodies in contact when both attain the same (equal) temperature. In this position they have no temperature difference.

Question 28.
Why is the handle of a press made of ebonite or wood?
Answer:
The handle of press is made of ebonite or wood, because ebonite and wood are bad conductors of heat. So the heat does not reach in our body.

Question 29.
Define radiation.
Answer:
The transfer of heat energy from a hot body to a cold body directly, without heating the space in between the two bodies is called radiation.

Question 30.
Define insulators.
Answer:
The materials which do not allow heat to pass through them easily are poor conductors of heat such as plastic and wood. Poor conductors are known as insulators.

Question 31.
What is thermos flask?
Answer:
Thermos flask is a device in which heat losses due to conduction, convention and radiation are minimised.

Short Answer Type Questions

Question 1.
The cooking utensils are made of metals like aluminium or copper while their handles are made of wood. Why?
Answer:
The cooking utensils are made of metals like aluminium or copper because these metals are good conductors of heat so they help in the transfer of heat.

The handles of cooking utensils are made up of bad conductors such as wood, plastic etc. As the handles made of bad conductors do not get heated up while cooking, we can hold them easily.

Question 2.
Kites and eagles fly without flapping their wings. Why?
Answer:
During the day, hot air surrounding the land gradually rises up and a convection air current develops. Kites and eagles move along this rising current without flapping the wings to fly high up in the sky.

Question 3.
Why do the birds puff up their feathers in winter?
Answer:
The birds puff up their feathers in winter, because in doing so they trap large amount of air, which in turn acts as an insulator and does not allow their body heat to flow out.

Question 4.
Explain briefly the formation of air currents.
Answer:
In coastal areas, during the day, the cool air blows from sea towmrds the land called sea breeze. During the night, the cool air blows from land to sea called the land breeze. This happens because of convection air currents. At night, land cools down much faster than sea. So, sea is warmer than land and the air current blows from land to sea. During the day, land is hotter than sea. As a result, the air rises up and cold air from sea blows towards the land to take its place.

Question 5.
Cement or concrete floors are made in pieces with metals or glass strips in between. Give reasons.
Answer:
It is done to allow for the expansion in summer and contraction in winter. If cement or concrete floors are made out in one continuous pieces. It would develop crackes due to contraction and expansion.

Question 6.
Room heaters have shiny reflectors. Why?
Answer:
Room heaters have shiny reflectors as the shiny surface absorbs very little heat. They reflect all the heat which makes the room heaters more effective.

Question 7.
Why is the handle of a pressure cooker covered with thick plastic?
Answer:
The handle of a pressure cooker covered with thick plastic, because plastic is a bad conductor of heat. Hence, the heat from the hot cooker does not flow to the handle, with the result that we can hold easily.

Question 8.
The desert sand is very hot in the day and very cool at night. Why?
Answer:
The desert sand has low specific heat capacity. So sand gets very hot in day time. During the night sand cools more quickly due to cold air which moves towards the sea.

Question 9.
Why is the handle of a metallic kettle covered with strips of cane?
Answer:
Cane strips is bad conductor of heat. Therefore, it cannot get heated when water is boiled in kettle. Therefore, the handle of a metallic kettle is covered with cane strips.

Question 10.
Why does the handle of an iron made of ebonite or wood?
Answer:
Ebonite or wood is a bad conductor of heat. Therefore, the heat from the iron is not conducted to the hand.

Question 11.
How does a blanket keep you warm in a cold night, even though it is not a source of heat?
Answer:
The blanket is made of wool, which is a bad conductor of heat. It has fine pores in which air is trapped which is also a bad conductor of heat. They do not allow heat to escape from our body to the surroundings. Therefore, the blanket keeps our body warm in winter.

Question 12.
Why are cloudy nights warmer than the clear nights?
Answer:
Cloudy nights are warmer than clear nights due to the fact that the heat which is radiated by the earth is again reflected back by the clouds. While on the other hand this phenomenon is not possible when the night is clear.

Question 13.
How are had conductors of heat useful in our daily life?
Answer:
Bad conductors are used for holding hot utensils in the kitchen. Bricks and mud which are bad conductors are used in building houses, especially in the ruler. regions. They keep houses warm in winter and cool in summer. The feathres of birds, hair and fur of animals keep them warm in winter, as they are bad conductor of heat.

Question 14.
Why do we wear woolen clothes in winter?
Answer:
Woolen clothes have fine pores filled with air. Wool and air are bad conductors of heat They do not allow heat of our bodies to escape out. Therefore woolen cloth keep the body warm in winter. And for the same reason we wear woolen cloth in winter.

Long Answer Type Questions

Question 1.
Describe briefly the process of conduction.
Answer:
Heat travels through solids by conduction only. The process of transmission of heat energy in solids without the actual movement of particles from their position is called conduction. Conduction takes place under the following conditions:
(i) A material medium that is compact.
(ii) No movement of any particle in the medium.
Thus, solids transmit heat though conduction. When a solid substance is heated, the particles that become hot start vibrating and pass on the excess energy to the neighbouring particles. This process continues till the whole body is heated. However during such an energy transfer, a particle does not change its position. Hence, heat is carried without the bodily movement of the particles.

There are some solids which allow the heat to pass through them. Such substances are called the conductors. Almost all metals such as iron, copper, silver, aluminium etc. are good conductors. The substances which do not allow the heat to pass through them are called the insulators. Wood, plastic, wool, clay etc. are bad conductors.

Question 2.
Write an experiment to prove that heat radiations can travel through vacuum.
Answer:
Take a flat bottomed flask. In the mouth of the flask fix a rubber stopper having two holes. Pass a thermometer through one hole and a glass tube with stopper through the other hole.

Remove air from the flask, by connecting to a vacuum pump. Record the temperature from the thermometer. Place the flask in bright sunlight or in front of an electric heater. It is observed that the thermometer records a rise in temperature. Thus, the experiment proves that transference of heat by radiaton requires no medium.

Question 3.
Explain the working of a thermos flask.
Answer:
Thermos flask is a special kind of flask for keeping liquids. It prevents loss or gain of heat by any of the three methods. It keeps liquid warm or cold for a long time. It was invented by Sir James Dewan in 1893.

It consists of a double-walled glass-cylinder. A vacuum is created in the space between the double walls. The two inner surfaces of glass walls are silvered. The flask is placed on a spring within a non-conduction cylindrical case to protect it from jerks and breakages. The gaps between flask and outer casing is packed with felt pads. The mouth of the flask is finally closed with a cork.

Since the container is made of glass which is a bad conductor of heat and therefore, the loss or gain of heat due to conduction is prevented. As there is vacuum between the double walls, it prevents transmission of heat by convection. Due to silvering of the inner surfaces, the heat loss by radiation is prevented. The cork and the felt pads also help to preserve the heat inside the flask. So, the hot liquids like tea, coffee, etc. remain hot and cold liquids like water, juice, etc. remain cold for a long time.

Question 4.
Write five applications of radiation.
Answer:
Applications of radiation:
(i) The base of cooking utensils is painted black so that it can absorb more heat and hence cooking is done fast.
(ii) Dark clothes are worn in winters as they absorb more heat from the sunlight and keep our body warm.
(iii) White clothes are worn in summer as they absorb very little heat and keep us cool.
(iv) Room-heaters have shiny reflectors as the shiny surface absorbs very little heat. They reflect all the heat which makes the room- heaters more effective.
(v) Crockeries are polished and painted white from outside so that they do not radiate heat easily.

Question 5.
Describe the process of radiation. How is it different from conduction and convection?
Answer:
Radiation is a process of transmission of heat in which heat energy travels in straight lines from hotter to cooler regions without the help of any intervening medium. It means that this process is different from the other two as it does not need any medium like conduction or convection. Radiation can take place in a vaccum. For example, heat from the sun reaches us through the outer space (vacuum) by means of radiation in the form of electromagnetic waves.

Differefnbe between radiation, conduction and convection:

Heat Class 7  HBSE Notes

• Our sense of touch is not always a reliable guide to the degree of hotness of an object.
• Heat: Heat is a form of energy which produces in us sensation of warmth. It causes hotness or coldness sensation in our body.
• Temperature: Temperature tells how hot a body is? Temperature of a body is the degree of hotness or coldness of the body.
• Heat flows in the direction of fall of temperature. Heat can be converted to other forms of energy like sound, light, mechanical energy etc. Other forms of energy can also be converted to heat energy.
• Effects of heat:
  (i) The object becomes hot.
  (ii) The object may expand in size.
  (iii) The object may change in state.
  (iv) Heat can speed up chemical reaction.
• Temperature is measured by a device called thermometer.
• The thermometer that measure our body temperature is called a clinical thermometer. The range of this thermometer is from 35°C to 42°C. For other purposes, we use the laboratory thermometers. The range of these thermometers is usually from 10°C to 110°c.
• The laboratory thermometer used in laboratories. It is called Celsius thermometer. It has one hundred markings on it.
• The melting point of pure ice is called lower standard point. Its value is 0°C.
• The boiling point of pure water is called upper standard point. Its value is 100°C.
• Transfer of heat: Heat flows from one body to another body by temperature difference. The flow of heat is from higher temperature to lower temperature. There are three different ways of heat transfer: conduction, convention and radiations.
• Conduction of heat: The process in which heat is handed over from one particle to another in the direction of fall of temperature without the actual movement of the particles of the medium is called conduction.
  
• Good conductor of heat: The materials which allow heat to pass through them easily, are called good conductor of heat. For example, silver, copper, aluminium, mercury etc. are good conductors of heat.
• Bad conductor of heat: The materials which do not easily allow heat to pass through them are called bad conductors of heat or insulators. Wood, plastics, mud, cork, cotton, ebonite, asbestos, most gases and liquids are bed conductor of heat.
• Convention of heat: Convention is a process by which heat is transferred from one part of a substance to another part through the actual movement of its constituents particles (atoms or molecules). Only liquids and gases convert heat. A solid cannot do so because solids do not flow like liquids or gases do.
• Radiation of heat: The process by which heat travels from one body to another without the intervention of any material medium is known as radiation.
  All hot objects transfer heat by radiation. Radiation does not require either a conducting medium or a convecting fluid. The sun transfers heat in all directions through the process of radiation. The radiations absorbed or emitted by a body depends upon the colour of the body.
  
• Thermos Flask (Vacuum Flask): Thermos flask is used to keep things warm and cold. It consists of a double walled glass flask, having vacuum between the walls, kept inside metallic case with the cork supporters.
  The outer and inner surfaces of the glass flask are highly silvered. The mouth of flask is fitted with air tight cork.
  
• The vacuum between the two walls of the flask prevents heat transfer by conduction or convection.
• The silver coating of the walls of the vessels reflects back heat radiations. Thus heat by radiation can neither enter inside the flask nor go out of the flask.
• The air-tight cork, which is a bad conductor of heat prevents any loss of heat by conduction or convection.
• Some heat may be transferred by conduction through thin glass walls at the neck and the poorly conducting cork.
• The total transfer of heat is very-very small, thus hot or cold liquid kept inside will keep its temperature for a long time.