CBSE Class 7

In this page, we are providing Food Where Does it Come From Forests: Our Lifeline Class 7 Extra Questions and Answers Science Chapter 17 pdf download. NCERT Extra Questions for Class 7 Science Chapter 17 Forests: Our Lifeline with Answers will help to score more marks in your CBSE Board Exams.

Class 7 Science Chapter 17 Extra Questions and Answers Forests: Our Lifeline

Extra Questions for Class 7 Science Chapter 17 Forests: Our Lifeline with Answers Solutions

Forests: Our Lifeline Class 7 Extra Questions Very Short Answer Type

Question 1.
Give four examples of forest animals.
Answer:
Tiger, lion, elephant, bear, etc.

Question 2.
What is meant by canopy?
Answer:
The branches of tall trees look like a roof over the other plants in the forest is called canopy.

Question 3.
Why do trees vary from place to place in their shapes and sizes?
Answer:
Because of different climatic conditions.

Question 4.
Define carnivores.
Answer:
The organisms which eat flesh and are dependent on other animals for food are called carnivores.

Question 5.
Define herbivores.
Answer:
The organisms which depend on plants or plant products for their food are called herbivores.

Question 6.
Give three examples of herbivores.
Answer:
Deer, elephant, rabbit.

Question 7.
How can the presence of an animal be recognised in the forest?
Answer:
By its droppings and footprints.

Question 8.
Define food web.
Answer:
Several interrelated food chains or feeding relationship among organism in an ecosystem is called food web.

Forests: Our Lifeline Class 7 Extra Questions Short Answer Type

Question 1.
Differentiate between autotrophs and heterotrophs.
or
Differentiate between producer and consumer.
Answer:

Question 2.
Give an example of food chain.
Answer:
Grass is eaten by insects, which in turn, is taken by the frog. The frog is consumed by snakes. This is an example of food chain.

Question 3.
Name any four birds which you expect to see in a forest.
Answer:
Kingfisher, blue jay, hornbill and jungle crow.

Question 4.
How does the forests floor look like?
Answer:
The forest floor looks dark-coloured and covered with a layer of dead and decaying fruits, plants, leaves, twigs and small herbs, which is quite moist and warm.

Question 5.
What do you mean by deforestation? Give some causes of deforestation.
Answer:
The excessive cutting of trees for personal or commercial purposes is called deforestation.
Two causes of deforestation are as follows:

1. Land is required to be cleared for cultivation, construction of houses, road, etc.
2. Forest fires cause huge loss to forest cover which may be natural or by man.
3. Overpopulation too directly affects forest covers with the expansion of his habitat.
4. Felling of trees recklessly for obtaining timber also causes deforestation.

Question 6.
What is the importance of dense bushes and tall grasses for animals living in the forests?
Answer:
The dense bushes and tall grasses provide the animals with food and shelter. Moreover, they protect the herbivores from carnivores living in the forest.

Question 7.
Why is it dark inside a forest?
Answer:
It is dark inside the forest because sun rays are hardly able to penetrate through the dense covering of leaves. The canopy of tall trees form a roof over the other plants. The trees also get covered with different types of creepers and climbers.

Question 8.
How does photosynthesis and respiration maintain the 02-C02 balance in the atmosphere?
Answer:
Photosynthesis is the process in which carbon dioxide gas is used and as a byproduct oxygen is given out. This oxygen is used by the animals for respiration and carbon dioxide is given out which is again used by green plants for photosynthesis.

Question 9.
How do forests help in bringing rain?
Answer:
Trees absorbs water from the soil through their roots, and the excess water is released in the atmosphere through transpiration in the form of water vapour. This released water vapour forms clouds which later bring rainfall.

Question 10.
Why are forests called green lungs?
Answer:
Forests, like lungs, maintain the 02-C02 balance in the atmosphere. Therefore forests are called green lungs.

Forests: Our Lifeline Class 7 Extra Questions Long Answer Type

Question 1.
Write the importance of forests.
or
Why forests are also known as our ‘lifeline’?
Answer:
The major importance of forests are following:

1. They maintain the 02-C02 balance in the atmosphere.
2. They maintain ground water level.
3. They prevent the soil from getting eroded.
4. They provide us with food, shelter, medicines, timber, wood and other useful products.
5. They maintain water cycle in the nature.

Question 2.
How does forests sustain a large variety of animals?
Answer:
Different types of animals live in the forest, like herbivores, carnivores, scavengers, etc. Forest provides them with suitable living conditions. The animals get their food in the forest itself. Herbivores feed on plants. Carnivores eat herbivores and thus survive. When these animals die, various scavengers like vultures, eagles, etc., feed on their dead bodies.

Numerous microorganisms also live in the forest that convert dead and decaying plant and animal tissues into humus. They are called decomposers. Thus, they provide a hostile condition for all the animals.

Question 3.
How do forests prevent soil erosion? Explain.
Answer:
The removal of top layer of fertile soil by the action of wind, river or rain is known as soil erosion. This can change a fertile land into a desert. This happens in areas which are not covered with vegetation like trees and plants.

The roots of plants and trees bind the soil particles together firmly. Owing to this, strong winds and flowing rivers find it very difficult to take away the particles of soil. In this way soil erosion is prevented.

When it rains heavily in a forests, the rainwater is first intercepted by the canopy and then it comes down through stem, branches and leaves of the forest plants. Over this process the speed of the rainwater slows down. In this way, the rainwater does not hit the floor of the forest directly. The forest floor covered with fallen, leaves and twigs absorbs water readily and do not allow it to flow and thus, also prevent soil erosion.

Question 4.
As an active citizen, elaborate your role in protecting the forests?
Answer:
At my level I will do the following things to protect the forest:

1. Use less paper and try to recycle it.
2. Do not buy any products made up of or obtained from killing of wild animals.
3. Try to plant as many trees as I can.
4. Aware people about the importance of forest in our lives.
5. Reduce use of artificial items as it also create stress on the forest.

Forests: Our Lifeline Class 7 Extra Questions HOTS

Question 1.
How do trees grow in the forest without human interference? Explain.
Answer:
Forest is a self-sustaining system. Forest floor is fertile due to presence of humus. Various agents like animals, wind, water, etc., disperse the seeds of many plants. When these seeds get the favourable conditions, like nutrient, water and proper temperature germinate into a seedling and gradually into a plant. Thus, no human interference is required for trees to grow in a forest.

Question 2.
Explain why a forest is called a ‘dynamic living entity’.
Answer:
Forests are called dynamic living entity because of the various plants, animals and microorganisms. The wide variety of animals helps the forest to regenerate and grow. Decomposers help in maintaining the supply of nutrients to the growing plants in the forest. Thus, in a nutshell forest is a dynamic living entity, full of life and vitality.

Question 3.
How do you think a bunch of seedlings sprouting on a heap of animal dropping in a forest will be benefitted?
Answer:
The decaying animal dropping will provide nutrients to the growing seedlings.

Question 4.
It is a matter of concern if any plants or animals perish from forest. Explain, why?
Answer:
Every component of a forest is dependent on other. If any of these component perish due to any adverse condition all other components of the forest get affected. For example, if herbivores are eliminated from the forest, then the forest will grow very dense due to no one to eat them and the carnivores will perish due to unavailability of food.

Forests: Our Lifeline Class 7 Extra Questions Value Based (VBQs)

Question 1.
Somya likes to buy books and copies. To finish a copy she wastes a lot of space and leave most of the pages blank. When she finds that her book shelf is full with old copies and books she just throw then in the dustbin. Once her cousin Abhishek visited her home. On seeing such a wastage of papers he said to her that this practice of hers is actually the cause of deforestation and she must stop this immediately.
(a) How wasting of papers are the cause of deforestation?
(b) How can we save papers?
(c) What value of Somya is shown here?

Answer:
(a) Papers are obtained from tree fibres. Making of papers causes felling of trees on a large scale. So wasting of papers mean making more papers which cause deforestation.
(b) We can save papers by following ways:

1. By recycling papers and using recycled papers.
2. By writing on both sides of papers.
3. By using all the space available on the paper.
4. By using paperless technologies like using phone or email to communicate, etc.

(c) Somya is passionate of buying books and copies without their requirement, extravagant, eco-unfriendly and immature.

In this page, we are providing Water: A Precious Resource Class 7 Extra Questions and Answers Science Chapter 16 pdf download. NCERT Extra Questions for Class 7 Science Chapter 16 Water: A Precious Resource with Answers will help to score more marks in your CBSE Board Exams.

Class 7 Science Chapter 16 Extra Questions and Answers Water: A Precious Resource

Extra Questions for Class 7 Science Chapter 16 Water: A Precious Resource with Answers Solutions

Water: A Precious Resource Class 7 Extra Questions Very Short Answer Type

Question 1.
What message do we get from water day?
Answer:
We celebrate water day to attract the attention of everybody towards the importance of conserving water.

Question 2.
What percentage of earth’s surface is covered with water?
Answer:
71%.

Question 3.
What is the two sources through which groundwater gets recharged?
Answer:
The rainwater and water from other sources such as rivers and ponds are the sources for recharging groundwater.

Question 4.
What will happen to plants if they do not get water for few days?
Answer:
Plants will wilt and ultimately dry-up if they are not watered for a few days.

Question 5.
List the main sources of underground water.
Answer:
Springs, tubewells, handpumps, etc.

Question 6.
What is water management?
Answer:
Minimum wastage of water is called water management.

Question 7.
Name the techniques of watering plants which minimises the wastage of water.
Answer:
Drip irrigation.

Question 8.
Why do certain regions on the earth become desert?
Answer:
Certain regions on the earth became desert because they got very little rain.

Question 9.
What is the minimum amount of water per person per day recommended by United Nations?
Answer:
50 Litres.

Question 10.
State any one way to prevent the wastage of water.
Answer:
There should not be any leakage in the supply lines.

Water: A Precious Resource Class 7 Extra Questions Short Answer Type

Question 1.
Define briefly what is water cycle.
Answer:
The continuous movement of water from the water bodies to the atmosphere and again back to the water bodies is called water cycle.

Question 2.
What do you mean by surface water?
Answer:
The water present on the surface of the earth is called the surface water.

Question 3.
What do you mean by rainwater harvesting?
Answer:
Collecting and conserving the rainwater from the roof tops of the buildings is called rainwater harvesting.

Question 4.
How is water table maintained below the earth?
Answer:
The rainwater and water from other sources seeping into the earth maintains the water table. This is called replenishing the water table.

Question 5.
What is the reason due to which earth appear blue from space?
Answer:
The earth appears blue from space because a major part of the surface of earth is covered with water in seas and oceAnswer:It is this water on the earth which makes it appear blue in colour.

Question 6.
What is drip irrigation?
Answer:
Drip irrigation is a technique of watering the plants by making use of narrow tubings which deliver water drop by drop directly at the base of the plant.

Question 7.
What is freshwater?
Answer:
The water that is fit for human consumption is called freshwater.

Question 8.
List the various reasons of depletion of water table.
Answer:
Following are the various reasons for depletion of water table:

1. Increase in population
2. Scanty rainfall
3. Deforestation
4. Agricultural activities
5. Industrialization
6. Decrease in the effective area of seepage of water.

Question 9.
What are bawris?
Answer:
Bawris are the old age practices of water storage and water recharge. It is a step well in which a person can go down by using set of steps to fetch water.

Water: A Precious Resource Class 7 Extra Questions Long Answer Type

Question 1.
What do you mean by conservation of water? How can we conserve water?
Answer:
The process of conservation of water is the wise and judicious use of water by us. We can conserve water by different ways. Rainwater harvesting minimises the wastage of water in houses and industries, us¬ing conservation techniques like drip irrigation in agriculture, etc., are few methods of conservation of water.

Question 2.
Explain briefly what is rainwater harvesting?
Answer:
Collecting and conserving the rainwater from the roof tops of the buildings is called rainwater 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 3.
List five advantages of conserving water.
Answer:
Following are the five advantages of conserving water:

1. Protects drinking water resources.
2. It solves the problem of water scarcity.
3. It helps to recharge groundwater.
4. It saves energy and money.
5. It save freshwater to run off into sea and ocean.

Question 4.
Explain how increasing population is responsible for the depletion of water table.
Answer:
Increasing population creates demands for construction of houses, shops, offices, roads and pavements. This decreases the open areas like parks and playgrounds. This in turn decreases the seepage of rainwater into the ground.

Moreover a huge amount of water is required for construction work and daily chores, often groundwater is used for this purpose. So on the one hand we are consuming more groundwater and on the other we are allowing lesser water to seep into the ground. This results in depletion of water table. In fact, the water table in some parts of many cities has gone down to alarmingly low levels.

Question 5.
How can you contribute towards water conservation?
Answer:
We can contribute towards water conservation by
(a) checking faucets and pipes for leaks.
(b) turning off taps while brushing
(c) mopping the floor instead of washing.
(d) using water after mopping to water the plants.
(e) using grey water from washing machine to flush the toilets.
(f) watering plants in evening and morning to avoid loss of water due to evaporation.

Water: A Precious Resource Class 7 Extra Questions HOTS

Question 1.
What is the source of water in each of the following?
(a) Wells
(b) Atmosphere
(c) Ground
Answer:
(a) Groundwater
(b) Evaporation (from ponds, lakes, transpiration, etc.)
(c) Rain (through infiltration)

Question 2.
Three-fourths of earth is covered with water, then why we need to conserve water?
Answer:
Seas and oceans occupy a vast per cent of water and is salty. This water is unfit for human consumption. Only a little per cent of water is freshwater. Out of this freshwater major portion is present in the frozen form in glaciers, ice caps and permanent snow. Thus, only a little is present as groundwater and much lesser than that as ponds, lakes, rivers, etc. So for our future we need to conserve water.

Question 3.
How scarcity of water can effect education of children?
Answer:
In water scarce area, children cannot attend school regularly since they spend hours in fetching water. Also, many children are not able to attend the school due to water-borne diseases caused due to absence of safe drinking water.

Question 4.
How scarcity of water can effect health as well as economy of an area?
Answer:
Water scarcity will force people to drink contaminated or polluted water. It may also lead to unhygienic conditions as our daily activities need lot of water to keep us clean. Thus, can lead to many infectious diseases. Neither small businesses or major global industries can function properly without water. Also, unhealthy people cannot work properly or able to attend a business. Thus, water scarcity effects health as well as economy of an area.

Water: A Precious Resource Class 7 Extra Questions Value Based (VBQs)

Question 1.
A bottle packaging company established in Rohan’s village started extracting a large quantities of water from the ground. It affected both the quantity and quality of water. All the wells in their village dried up. Women now had to walk nearly five kilometres to fetch water. All the villagers united to protest against the packaging company and led to its permanent closure.
(a) Why the wells in village dried up?
(b) How the quality of groundwater deteriorates due to over-extraction?
(c) How can groundwater be replenished again?
(d) What value of villagers are shown here?

Answer:
(a) Wells in the village dried up due to over-exploitation of groundwater by the packaged drinking water company.
(b) Excessive pumping in coastal areas cause saltwater to move inland and upward, resulting in saltwater contamination of the water supply.
(c) Groundwater can be replenished again through rainwater harvesting by building bunds, check- dams and other methods which helps in much percolation of water into the ground. By planting more and more trees, i.e., reforestation, groundwater level can be increased.
(d) Villagers are conscious of their rights and duty to mother nature, and united.

Question 2.
Water is one of the most important compound for all living things. There can be no life without it. Empty water pots, long queue of women and children, people jostling to get a bucket of water when a tanker arrives, etc., are common scenes at the onset of summer or in water-scarce area. Still many people who are blessed with this precious gift, water, do not bother to waste it thoughtlessly.
(a) Do you think that handling the most precious gift of nature thoughtlessly is correct?
(b) In your level how would you try to minimise the wastage of water?
(c) Write two slogans for conserving water.

Answer:
(a) No.
(b)

1. Close the tap while brushing.
2. Check for leaking taps and water pipes.
3. Use water from mopping for watering plants
4. Help in spreading water education and creating awareness amongst the masses.

(c)

1. Water water everywhere, try to save it if you care’.
2. ‘Slow the; flow, save H20’.

In this page, we are providing Light Class 7 Extra Questions and Answers Science Chapter 15 pdf download. NCERT Extra Questions for Class 7 Science Chapter 15 Light with Answers will help to score more marks in your CBSE Board Exams.

Class 7 Science Chapter 15 Extra Questions and Answers Light

Extra Questions for Class 7 Science Chapter 15 Light with Answers Solutions

Light Class 7 Extra Questions Very Short Answer Type

Question 1.
What type of mirror is used as a side view mirror in a scooter?
Answer:
Convex mirror.

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

Question 3.
What happens when a beam of light enters a prism?
Answer:
The beam of light splits into seven colours.

Question 4.
Define briefly a convex mirror.
Answer:
A mirror which reflects the light from its inner polished side is a convex mirror.

Question 5.
When we see an ambulance we see that the letters which actually appears to right is seen by us on left side. What is this effect called?
Answer:
This effect is called lateral inversion.

Question 6.
What is virtual image?
Answer:
The image which cannot be obtained on a screen is called a virtual image.

Question 7.
What is a lens?
Answer:
A lens is a piece of refracting transparent medium bounded by two surfaces in which at least one has curved surface.

Question 8.
Name the two type of lenses.
Answer:

• Concave lens
• Convex lens.

Question 9.
What kind of image is formed by concave lens?
Answer:
A concave lens always forms erect, virtual and smaller image than the object.

Question 10.
What is prism?
Answer:
The transparent glass pyramid bounded by four triangular surfaces that separate white light into spectrum of colours is called prism.

Question 11.
What are spherical mirrors?
Answer:
The mirrors which have curved surface are known as spherical mirror.

Light Class 7 Extra Questions Short Answer Type

Question 1.
What is regular reflection?
Answer:
When parallel rays of light fall on a smooth or polished surface, the reflected rays are parallel to each other. This is called regular reflection.

Question 2.
List two uses of concave mirror.
Answer:
Following are two uses of concave mirror:
(i) It is used by dentists and doctors.
(ii) Concave mirrors are used in head lights of the cars, buses, shaving mirror, etc.

Question 3.
What is the kind of image formed by a concave mirror?
Answer:
Concave mirror forms real and inverted image but when the object is placed very near to the mirror then the image formed to be virtual erect and magnified.

Question 4.
List two uses of convex mirror.
Answer:Following are the two uses of convex mirror:
(i) It is used as a side view mirror to help the drivers to see the traffic behind them.
(ii) It is used in shops, parking lots, etc., to get larger view of the area.

Question 5.
State any two uses of convex lens.
Answer:
(i) It is used as a magnifying glass in hand lenses, microscope, telescope, etc.
(ii) It is used in spectacles to correct far-sightedness.

Question 6.
What is light?
Answer:
Light is a form of electromagnetic radiation (radiation energy) which produces in us the sensation of vision. Light travels along a straight line.

Question 7.
What are the characteristics of image formed by a convex mirror?
Answer:
Following are the characteristics of image formed by a convex mirror:

1. Image is erect.
2. The image is smaller than the object.
3. The image formed is virtual.

Light Class 7 Extra Questions Long Answer Type

Question 1.
Differentiate between the following:
(a) Convex mirror and convex lens
(b) Concave mirror and concave lens
(c) Convex mirror and concave mirror
Answer:

Question 2.
What are the characteristics of images formed by a concave mirror?
Answer:
Following are the characteristics of images formed by a concave mirror:

1. The image is not always of the same size as the object.
2. The image is formed on the screen and the type of images which are formed on screen are called real images.
3. The image is inclined when the object is kept far away from the mirror. When it is brought very close to the concave mirror, an erect and enlarged image is formed.

Question 3.
What is meant by spectrum? Name the colours of spectrum in their order.
Answer:
The band of seven colours dispersed by a glass prism is known as spectrum. The seven colours in a spectrum are violet, indigo, blue, green, yellow, orange, and red. It is also abbreviated as VIBGYOR.

Question 4.
Write a short note on Newton’s disc.
Answer:
A Newton disc, invented by Isaac Newton, is a disc with seven segments in rainbow colours. When the disc is rotated fast, the colour get mixed together and the disc appears to be whitish. This is due to the phenomenon called persistence of vision. It was an important discovery as it proves that light is not white, but a mixture of colour. The seven colours used to paint Newton disc are violet, indigo, blue, green, yellow, orange and red. See Fig. 15.16.

Light Class 7 Extra Questions HOTS

Question 1.
Rajesh for observing dispersion of light, used light from laser torch to fall on a prism. Will he be able to observe a band of seven colours?
Answer:
No, because laser torch gives out light of only one colour.

Question 2.
If the side mirror of a scooter is replaced by a plane mirror, will it cause any inconvenience to the driver?
Answer:
Yes, it will cause inconvenience to the driver and he will not be able to see the traffic behind him properly.

Question 3.
The concave reflecting surface of a torch got rusted. What effect would this have on the beam of light from the torch?
Answer:
The beam of light will be of lower intensity due to diffused or irregular reflection.

Question 4.
How can you obtain a real image of a distant object?
Answer:
By using concave mirror or convex lens and a screen we can obtain a real image of a distant object.

Question 5.
How will you identify the three mirrors, i.e., convex, concave and plane mirror without touching them?
Answer:
We can identify the mirrors by seeing the image formed by them.

1. Images formed by plane mirror is always virtual, erect and of same size as that of object.
2. Images formed by convex mirror is erect, virtual and smaller in size than the object.
3. Image formed by concave mirror is real, inverted, virtual, erect, magnified and diminished depending upon the distance of object with respect to the mirror.

Light Class 7 Extra Questions Value Based (VBQs)

Question 1.
Vinita thought to make a solar cooker and she shared her idea with Ankita. Ankita felt very excited that Vinita is using one of the renewable source of energy. Ankita suggested Vinita to use concave mirror instead of plane mirror as reflector to get the maximum heat. Vinita liked the idea of Ankita and thanked her for valuable suggestion.
(a) What is a solar cooker? What is its use?
(b) Why concave mirror is better than plane mirror for getting maximum heat?
(c) Can you name other such devices which are sources of energy and are eco-friendly.
(d) What values of Ankita and Vinita are shown here?

Answer:
(a) A solar cooker is a device which uses the energy of direct sunlight to heat, cook or pasteurize food or drink.
(b) Concave mirror converges the sunlight to a single point. Thus, generates more heat and cook the food faster.
(c) Solar water heater, wind mills, solar cells, etc.
(d) Ankita and Vinita, both, are eco-friendly, suggestive, friendly and caring to each other.

In this page, we are providing Electric Current and Its Effects Class 7 Extra Questions and Answers Science Chapter 14 pdf download. NCERT Extra Questions for Class 7 Science Chapter 14 Electric Current and Its Effects with Answers will help to score more marks in your CBSE Board Exams.

Class 7 Science Chapter 14 Extra Questions and Answers Electric Current and Its Effects

Extra Questions for Class 7 Science Chapter 14 Electric Current and Its Effects with Answers Solutions

Electric Current and Its Effects Class 7 Extra Questions Very Short Answer Type

Question 1.
What is a battery?
Answer:
When two or more cells are joined together, it is called a battery.

Question 2.
Name the effects of electric current.
Answer:

• Heating effect
• Magnetic effect
• Chemical effect

Question 3.
What is a circuit diagram?
Answer:
It is a symbolic representation of an electric circuit.

Question 4.
Which property of a conducting wire is utilised in making electric fuse?
Answer:
Low melting point of the wire.

Question 5.
What happens if the filament of the bulb is broken?
Answer:
The circuit would be incomplete and the bulb does not glow even if the switch is in the ‘ON’ position.

Question 6.
What is the use of a cell holder?
Answer:
A cell holder is used to make battery of two or more cells.

Question 7.
How are the cells placed in the cell holder?
Answer:
The cells are placed in the cell holder such that the positive terminal of one cell is connected to the negative terminal of the next cell.

Question 8.
Give two examples of the heating effect of current.
Answer:
(i) Electric kettle
(ii) Hair dryers

Question 9.
Why should we buy electric appliances with the ISI mark?
Answer:
The ISI mark ensures that the appliance is safe and wastage of energy is minimum. So we should buy only electric appliances with the ISI mark.

Question 10.
Name the device used to protect damages to the circuit due to excessive flow of current.
Answer:
Electrical fuse or MCB.

Question 11.
What happens if by accident the current exceeds the safe limit?
Answer:
The wires may become overheated and may cause fire.

Question 12.
What is a fuse?
Answer:
A fuse is a safety device which prevents damages to electrical circuits and possible fires.

Question 13.
Who was the first person to notice the deflection of compass needle every time the current was passed through the wire?
Answer:
Hans Christian Oersted.

Question 14.
What do the doctors use to take out small pieces of magnetic material accidently fallen in the eye?
Answer:
Doctors use tiny electromagnets for this purpose.

Question 15.
Give one reason for short circuit.
Answer:
Direct touching of wires with each other.

Question 16.
Why is an electric fuse required in all electrical appliances?
Answer:
It is required to check excessive flow of electric current and save electrical appliances from further damage.

Question 17.
Why is it advisable not to touch a lighted electric bulb connected to the mains.
Answer:
Lighted electric bulb connected to the mains may be very hot and can burn our hand badly.

Electric Current and Its Effects Class 7 Extra Questions Short Answer Type

Question 1.
Define a battery. Explain the arrangement of cells in a battery.
Answer:
A battery is a combination of two or more cells in which cells are placed such that the positive terminal of one cell is connected to the negative terminal of the next cell. Many devices like torches, transistors, toys, TV remote controls, etc., use batteries. The cells are sometimes placed one after the other and sometimes side by side.

Question 2.
When does the current flow throughout the circuit? Explain.
Answer:
When the switch is in the ‘ON’ position, and the positive terminal of the battery is connected to the negative terminal of the battery through wires then the circuit is said to be closed and the electric current flows throughout the circuit.

Question 3.
How many types of circuit are there? Describe.
Answer:
There are two types of circuit

1. closed circuit and
2. open circuit.

(i) Closed-circuit: When the switch is in the ‘ON’ position and the circuit from the positive terminal of the battery to the negative terminal is complete then the circuit is said to be closed and the current flows throughout the circuit. Also the bulb glows in the closed circuit.
(ii) Open circuit: When the switch is in the ‘OFF’ position or the filament of the bulb is broken, the circuit is incomplete and it is said to be an open circuit. No current flows through any part of the circuit.

Question 4.
Why are wires of different materials and different lengths and thicknesses used?
Answer:
The amount of heat produced in a wire depends on its material, length and thickness. Thus for different requirements, the wires of different lengths and thickness and materials are used.

Question 5.
What type of wire is used for making electric fuses?
Answer:
Wires made of some special materials that melt quickly and break when large electric currents are passed through them are used for making electric fuses. For example, alloy of lead and tin.

Question 6.
What is an electromagnet?
Answer:
A coil that behaves like a magnet when electric current is passed through it and loses its magnetism when the supply of electricity is broken is called an electromagnet. It is a temporary magnet made by coiling wire around an iron core; when current flows in the coil the iron behaves as a magnet. Electromagnets can be made very strong and can lift heavy loads.

Electric Current and Its Effects Class 7 Extra Questions Long Answer Type

Question 1.
Explain the working of an electric bell with diagram.
Answer:
It consists of a coil of wire wound on an iron piece. The coil acts as an electromagnet. An iron strip with a hammer at one end is kept close to the electromagnet. There is a contact screw near the iron strip.

When the iron strip is in contact with the screw, the current flows through the coil which becomes an electromagnet. It, then, pulls the iron strip. In the process, the hammer at the end of the strip strikes the gong of the bell to produce a sound. However, when the electromagnet pulls the iron strip, it also breaks the circuit.

The current through the coil stops flowing and the coil is no longer behaves as an electromagnet. It no longer attracts the iron strip. The iron strip comes back to its original position and touches the contact screw again.

This completes the circuit. The current flows in the coil and the hammer strikes the gong again. This process is repeated in quick succession. The hammer strikes the gong every time the circuit is completed. This is how the bell rings.

Question 2.
When does an electric short circuit occur? What harm can it do?
Answer:
When the plastic covering of both live wire and neutral wire removes due to wear and tear, these two wires come in contact with each other. Since, the resistance of neutral wire is very low, excessive current flow through the wire in a short time which heats the wire to a great extent. This can result in fires. Another reason of short circuiting is connection of many devices to a single socket. This can also lead to excessive flow of current.

Question 3.
What do you mean by overloading of an electric circuit? State two measures to avoid overloading.
Answer:
The current flowing in domestic wiring at a particular time depends on the power ratings of the appliances which are being used. When a number of appliances are switched on at the same time, they take out an extremely large amount of current. This is called ‘overloading the circuit’. Now due to an extremely large amount of current flowing through them, the copper wires of household get heated to a very high degree and a fire may be started.

Two measures to avoid overloading are following:

• Too many appliances should not be connected to a single socket.
• Many electrical appliances of high power rating should not be run at the same time.

Question 4.
Explain construction of a simple electromagnet with a labelled diagram.
Answer:
An electromagnet act on the principle of magnetic effect of the current. The coil of wire wound around an iron bar behaves like a magnet when electric current flows through it. When electric current is switched off, the coil generally loses its magnetism.

To construct an electromagnet, take a big iron nail or a big iron screw. Take a long piece of insulated copper wire and wind quite a few turns around the nail. Connect the ends of the wire to the terminals of a battery through a switch as shown in Fig. 14.19.

Place some pins on or near the end of the nail. Now switch on the current. You will observe that pins cling to the nail. Now switch off the current. You will observe that pins no longer get attracted to the nail.

Electric Current and Its Effects Class 7 Extra Questions HOTS

Question 1.
Why do birds do not get shock when they sit on high power live wire but we do?
Answer:
As bird sit on only one wire, the circuit remains incomplete so they do not get shock.

Question 2.
Why are compact fluorescent lamps (CFLs) preferred over electric bulbs?
Answer:
CFLs do not waste electricity as heat and thus consumes less energy whereas electric bulb along with light also give out heat.

Question 3.
Why are MCB preferred over electric fuses?
Answer:
Due to following reasons MCB are preferred over electric fuses:

1. MCB is more sensitive to overcurrent than fuse.
2. Restoration of electric supply is quick. Restoration can be done by just switching the operating knob to its ‘ON’ position
3. Handling MCB is electrically more safe than fuse.

Question 4.
Can we use same fuse in a geyser and a television set or any other electrical appliances? Explain.
Answer:
No, different electrical appliances need different amount of current. A geyser generally takes more voltage of current in comparison to a television. Therefore the fuse in these will be of different ratings.

Question 5.
Why we must cover plug pin holes which are within the reach of children with cellotape or a plastic cover when not in use?
Answer:
Children are usually not aware of electrocution and they can put their fingers or other conducting material into the plug pin holes. To protect them from electric shock we must cover plug pin holes with cellotape or plastic cover.

Electric Current and Its Effects Class 7 Extra Questions Value Based (VBQs)

Question 1.
Rama saw her mother running microwave oven, electric cooker and mixer grinder from a single socket. She immediately rushed to her mother and reminded her of overloading and its consequences. Rama’s mother immediately turned off the switch and connected them one by one according to her need. She felt very happy for Rama for her presence of mind.
(a) What is overloading?
(b) What are the consequences of overloading?
(c) What role do MCB plays in case of overloading?
(d) What value of Rama is shown here?

Answer:
(a) When excessive amount of electric current passes through the wire, excessive heating take place, this is called overloading.
(b) Overloading can damage the circuit of house. It can also lead to fire.
(c) When there is overloading of current, MCB trips and switches off, which in turn cut off the supply of electricity and thus protect us from damages due to overloading of current.
(d) Rama is an intelligent, quick decision maker and helpful girl.

Question 2.
Class VII students thought to organise an campaign on ‘conserve energy’ in which they will include how to conserve electricity and what precautions one must take while handling electricity.
(a) Imagine that you are also participating in this campaign. What will you do to make it more effective and interesting?
(b) What precautions one must observe while working with the electricity.
(c) How can you conserve electricity?
(d) Do you think you also need to run an awareness campaign on certain problem or crisis related to your area. Why?

Answer:
(a) We can make it more effective and interesting by organising play and some cultural programmes.
(b) Following precautions must be observed while working with the electricity:

1. Do not touch switches with wet hand.
2. All appliances must be properly earthed.
3. Wear rubber shoes and gloves before coming in contact with electrical wire during repair or replacement.
4. Do not conduct experiment with main supply.

(c) Use CFL bulb or tubelights.

1. Switch off lights, fans, TV, etc., when not needed.
2. Always run AC in auto mode
3. Install efficient electrical appliances which consume less current.

(d) Do it yourself.

In this page, we are providing Motion and Time Class 7 Extra Questions and Answers Science Chapter 13 pdf download. NCERT Extra Questions for Class 7 Science Chapter 13 Motion and Time with Answers will help to score more marks in your CBSE Board Exams.

Class 7 Science Chapter 13 Extra Questions and Answers Motion and Time

Extra Questions for Class 7 Science Chapter 13 Motion and Time with Answers Solutions

Motion and Time Class 7 Extra Questions Very Short Answer Type

Question 1.
What is the use of speedometer?
Answer:
Speedometer is a device which is used in vehicles to measure the distance covered by the vehicle.

Question 2.
What is uniform motion?
Answer:
Uniform motion is that type of motion in which body travels equal distances in equal intervals of time.

Question 3.
What is speed?
Answer:
The speed of an object is defined as the distance travelled by the object in unit time.

Question 4.
State the formula of average speed of an object.
Answer:
Average speed = \(\frac{\text { Total distance travelled }}{\text { Total time taken }}\)

Question 5.
Which unit of speed will you use to express the speed of an aeroplane?
Answer:
km/s

Question 6.
Which kind of motion is described by a freely falling body?
Answer:
Linear motion.

Question 7.
What is the name of the device which measures the speed of a moving vehicle?
Answer:
Odometer

Question 8.
If A covers a certain distance in 30 minutes and B covers the same distance in 45 minutes, then who is travelling in higher speed?
Answer:
A is taking less time to cover the same distance, so it is travelling in higher speed.

Question 9.
What is the relation between distance and speed?
Answer:
Distance = Speed × Time

Question 10.
On what the time period of a simple pendulum depends?
Answer:
The time period of a simple pendulum depends upon its length.

Motion and Time Class 7 Extra Questions Short Answer Type

Question 1.
Describe how we calculate time period of a simple pendulum.
Answer:
The time period of a simple pendulum is the time taken by it to travel from A to B and back to A. When the bob moves from one extreme position A to the other extreme position B and comes back to A, it completes one oscillation.

Question 2.
What is motion? Describe briefly.
Answer:
An object that is moving with respect to time and another body is said to be in motion. Motion is measured as the distance covered by an object in a specific interval of time.

Question 3.
Differentiate between slow and fast objects.
Answer:
An object which takes longer time to cover a certain distance is called slow whereas another object which takes a shorter time to cover the same distance is called fast.

Question 4.
Anshika takes 15 minutes from her house to reach her school on bicycle the distance between her house and the school.
Answer:
Time taken = 15 min.
Speed = 2 m/s
Distance = Speed × time
= 15 × 60 × 2 = 1800 m
Thus, the distance between Anshika’s house and her school is 1800 m.

Question 5.
Draw the distance-time graph to show a car moving with a constant speed.
Answer:

Question 6.
What are the factors on which time period of a pendulum depends?
Answer:
Following are the factors on which time period of a pendulum depends:

• Length of the string of the pendulum.
• Acceleration due to gravity.

Question 7.
State one factor which is common in all the clocks.
Answer:
All the clocks show periodic motion.

Motion and Time Class 7 Extra Questions Long Answer Type

Question 1.
State the difference between uniform motion and non-uniform motion.
Answer:

Question 2.
Represent the following graphically:
(a) An object at rest
(b) An object moving with uniform speed
(c) An object moving with non-uniform speed
Answer:

Question 3.
The odometer of a car reads 24830 km at 1:25 PM, 24865 km at 2:05 PM and 25005 km at 3:15 PM. Calculate the speed of the car in km/h and m/s from 1:25 PM to 3:15 PM.
Answer:
D₁ = 24865 – 24830 = 35 km t₁ = 2:05 – 1:25 = 40 min
D₂ = 25005 – 24865 = 140 km t₂ = 3:15 – 2:05 = 50 min

Hence, speed of car is 116.7 km/h and 32.407 m/s.

Question 4.
Motion of A, B, C and D is plotted on a distance-time graph below. Study the graph and answer the following questions:

(a) Who is travelling fastest?
(b) Who is at rest?
(c) Who is moving in uniform motion?
(d) Who is accelerating with time?
(e) Who is moving slowest?
Answer:
(a) A
(b) C
(c) A
(d) B
(e) D

Question 5.
A scooter during its journey covers certain distances at different time intervals. Plot a graph by considering the following data and selecting a suitable scale. State whether the motion is uniform or nonuniform motion.

Answer:

The distance-time graph is a straight line so the motion of the scooter is uniform motion.

Motion and Time Class 7  Extra Questions HOTS

Question 1.
Complete the data of the table given below with the help of the distance-time graph.

Answer:

Hence, the data is

Question 2.
Starting from A, Somnath moves along a rectangular path ABCD as shown in Fig. 13.14. He takes 3 minutes to travel each side. Plot a distance-time graph and explain whether the motion is uniform or non-uniform. Find average speed of Somnath to move along the rectangular path.
Answer:



Since the distance covered per unit time for the entire distance is not the same, the motion is non-uniform motion.

Question 3.
The average age of students of class VII B is 12 years 4 months. Express the age in seconds.
Answer:
12 years 4 months = 12 × 365 + 4 × 30 = 4500 days
4500 days = 4500 × 24 × 60 × 60 = 388800000 s

Question 4.
Sitting in a classroom each student appears stationary to each other, whereas actually they are in motion. Explain.
Answer:
This is because of the earth in which we live is always in a state of motion around the sun and also along its axis.

Motion and Time Class 7 Extra Questions Value Based (VBQs)

Question 1.
Ritesh was riding a bicycle on the road, he said that the wheels of the bicycle are moving along a straight line. But his friend. Saket, who was also riding a bicycle said that the wheels of the bicycle are moving circular. They then decided rather than fighting among themselves it is better to ask their science teacher.
(a) Write some types of motion.
(b) What is rectilinear motion.
(c) What is rotatory or circular motion.
(d) Who among, Ritesh and Saket, is correct? Explain.
(e) What value of Ritesh and Saket is shown here?

Answer:
(a) Rectilinear motion, oscillatory motion, rotatory motion, random motion, etc.
(b) When the motion of a body is along a straight line, it is known as rectilinear motion.
(c) When a body moves about a fixed axis without changing its position, the body is said to have a rotatory motion.
(d) Ritesh and Saket, both are correct because wheels of the bicycle is showing both types of motion, i. e., rectilinear motion along the road as well as rotational or circular motion along a fixed axis.
(e) Ritesh and Saket both are intelligent and mature enough to not quarrel and inquisitive