Heat Transfer in Nature Class 7 Extra Questions and Answers Science Chapter 7

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Class 7 Science Chapter 7 Heat Transfer in Nature Extra Questions

Class 7 Science Chapter 7 Extra Questions on Heat Transfer in Nature

Heat Transfer in Nature Class 7 Very Short Question Answer

Question 1.
Shopkeepers selling ice blocks usually cover them with jute sacks. Explain why.
Answer:
The layers of Jute traps the air in between the fibres. The trapped air prevents the flow of heat from surroundings to the ice and hence prevents it from melting.

Question 2.
Why do we wear light coloured cotton clothes when it is hot?
Answer:
Light coloured cotton clothes give us a feeling of coolness by reflecting heat.

Question 3.
What do you mean by the transfer of heat?
Answer:
The heat flows from a hotter object to a colder object. This process is called transfer of heat.

Question 4.
How does heat transfer in water or air?
Answer:
By convection

Question 5.
How does heat transfer in solids?
Answer:
By conduction

Question 6.
To keep her soup warm, Paheli wrapped the container in which it was kept with a woollen cloth. Can she apply the same method to keep a glass of cold drink cool? Give reason for your answer.
Answer:
Yes, she can. The air trapped between the layers of wool is a poor conductor of heat. The trapped air prevents the flow of heat from surroundings to get inside the woollen layers and vice versa and hence prevents it from getting cool down or getting warm respectively.

Question 7.
Give two examples each of conductors and insulators of heat.
Answer:
Conductors aluminium, iron Insulators plastic, wood.

Question 8.
What are conductors?
Answer:
Substances which allow heat to pass through them are called conductors.

Question 9.
What are insulators?
Answer:
Materials which do not allow heat to pass through them are called insulators.

Question 10.
What is sea breeze?
Answer:
The movement of air from the sea towards the land during daytime in coastal areas is called the sea breeze.

Question 11.
What is land breeze?
Answer:
The cool air from the land moves towards the sea at night in coastal areas is called land breeze.

Question 12.
Name the form of energy that causes hotness or coolness.
Answer:
Heat.

Question 13.
What are the various methods of transfer of heat?
Answer:
There are three methods of transfer of heat:

1. Conduction
2. Convection
3. Radiation

Question 14.
What is infiltration?
Answer:
It is the process by which water from the surface of the Earth passes through the soil and rocks, and gets stored as groundwater beneath the Earth’s surface.

Question 15.
Name the processes involved in the water cycle.
Answer:
The main processes involved in the water cycle are:

1. Evaporation
2. Condensation
3. Precipitation
4. Transpiration

Question 16.
Name the underground layers that stores water.
Answer:
Aquifers

Question 17.
What ensures that the groundwater sources are recharged?
Answer:
The water cycle

Question 18.
Why can water move through gravel more easily?
Answer:
Because the spaces between the gravel particles are wider and open.

Question 19.
What is transpiration?
Answer:
It is process by which water evaporates from the leaves of trees and plants.

Question 20.
What does water cycle helps in?
Answer:
Water cycle helps in redistribution and replenishment of water in rivers, lakes and oceans.

Question 21.
When does land breeze occurs?
Answer:
It occurs at night.

Question 22.
When does sea breeze occurs?
Answer:
It occurs during the day.

Question 23.
What is radiation?
Answer:
It is the process of transfer of heat in which no medium is required.

Question 24.
Why does hot air rise?
Answer:
Hot air expands, becomes lighter and rises up.

Question 25.
What happens when a partially inflated balloon is placed in the Sun?
Answer:
When the air inside the balloon is heated, it expands, causing the balloon to increase in size.

Question 26.
Which process brings rain, snow and hail?
Answer:
Precipitation.

Question 27.
What is groundwater?
Answer:
Water stored in underground pore spaces of soil and rocks is called groundwater.

Question 28.
Name one method to recharge groundwater.
Answer:
Rainwater harvesting

Question 29.
What do you mean by convection?
Answer:
The process of hotter liquid or gases transferring heat to the colder surroundings is known as convection.

Heat Transfer in Nature Class 7 Short Question Answer

Question 1.
Look at figure. Mark where the heat is being transferred by conduction, by convection and by radiation.

Answer:

Question 2.
In the arrangements A and B shown in Figure, pins P and Q are fixed to a metal loop and an iron rod with the help of wax. In which case are both the pins likely to fall at different times? Explain.

Answer:
In case of ‘B’ the pin at position P will fall first followed by pin at position Q as the heat will reach pin P first. Whereas in case of ‘A’ the heat will travel in both the directions and as a result pins at position P and Q will fall simultaneously.

Question 3.
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 wall of houses be painted white because white colour reflects heat and the houses do not heat up too much.

Question 4.
For setting curd, a small amount of curd is added to warm milk. The microbes present in the curd help in setting if the temperature of the mixture remains approximately between 35°C to 40°C. At places, where room temperature remains much below the range, setting of curd becomes difficult. Suggest a way to set curd in such a situation.
Answer:
To maintain the favourable temperature for the microbes to turn the milk to curd, the container can be wrapped by woollen material so that the wool used will trap the air in between. The trapped air will prevent the flow of heat from surroundings to get inside the woollen layers and vice versa and hence prevents it from getting cool down or getting warm respectively. The container can also be kept in the sun.

Question 5.
Complete the following table:
Table: Hot and cold objects

Object	Cold/ Cool	Warm/ Hot
Ice cream
Spoon in a tea cup
Fruit juice
Handle of a frying pan

Answer:

Object	Cold/ Cool	Warm/ Hot
Ice cream		–
Spoon in a tea cup	–
Fruit juice		–
Handle of a frying pan	–

Question 6.
What do you mean by conduction mode of transfer of heat energy?
Answer:
The process by which heat is transferred from hotter end to colder end of a metal is called conduction. In this process, molecules of the substance do not move but heat energy is transferred. In solids generally, the heat is transferred by the process of conduction.

Question 7.
Why is the handle of a metallic kettle covered with strips of cane?
Answer:
Handle of metallic kettle is covered with strips of cane because when kettle is heated, the heat does not pass through strips of cane. The strips of cane are bad conductor of heat and we may hold the handle with our bare hands.

Question 8.
Why is it more comfortable to wear white or light coloured clothes in summer and dark coloured clothes in winter?
Answer:
Light coloured clothes reflect most of the heat that falls on them and we feel more comfortable wearing them in summer. Dark clothes absorb more heat so we feel comfortable with dark coloured clothes in winter.

Question 9.
How do woollen clothes keep us warm in the winter?
Answer:
The wool fibres trap the air in between them. This air prevents the flow of heat from our body to the cold surroundings. So, we feel warm.

Question 10.
How does the heat comes towards us from the sun?
Answer:
When we come out in the sun, we feel warm. The heat comes to us by the process called radiation from the sun. It can take place whether a medium is present or not.

Question 11.
You are given a thick blanket and a combination of two thin blanket joined together. Which one of these two blankets will you choose?
Answer:
Suppose we are given the choice in winter of using either a thick blanket or two thin blankets joined together, then we select the blanket which is formed by the joining of two blankets because there would be layer of air in between the blankets. The air is poor conductor of heat. So this blanket gives more warmth.

Question 12.
Discuss why wearing more layers of clothing during winter keeps us warmer than 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. Air is a bad conductor, it does not allow the body heat to escape.

Question 13.
While constructing a house in a coastal area, in which direction should the windows preferably face and why?
Answer:
The windows of houses in coastal areas should preferably face towards the sea as the blowing sea breeze will keep house cool to some extent during the daytime.

Question 14.
Explain the seepage of water.
Answer:
When it rains, some of the water flows into ponds, lakes, and oceans, while some seeps into the ground. This process is called infiltration. Water passes through the soil and porous rocks and is stored in the spaces between sediments and rocks below the ground. This stored water is called groundwater, and it can be extracted by digging wells or drilling borewells.”

Heat Transfer in Nature Class 7 Long Question Answer

Question 1.
Explain the sea breeze and land breeze.
Answer:
At sea-shore during the day, cold air from the sea moves towards the land because the land gets more heated than the sea water. Hot air above the land rises up, and cold air from the sea moves towards the land. This is called sea breeze as shown in Fig.(a).

At night, cold air from the land moves towards the sea because the land cools more quickly than the sea water. So hot air above the sea rises up and cold air from the land moves towards the sea. This is called land breeze as shown in Fig.(b)

Fig. (a) sea breeze (b) Land breeze

Question 2.
Explain radiation.
Answer:
The mode of transfer of heat energy in which no medium is needed to transfer heat from a hotter body to a colder body is called radiation. The heat from the sun comes to the earth without any medium thereby using the mode of radiation. Also, all objects exchange heat with their surroundings through the process of radiation.

Question 3.
At a camp site, there are tents of two shades – one made with black fabric and the other with white fabric. Which one will you prefer for resting on a hot summer afternoon? Give reason for your choice. Would you like to prefer the same tent during winter?
Answer:
It is better to prefer the white tent during summer because light colours being the best reflectors of heat falling on them will reflect maximum amount of heat they will receive and will make the tent cool to some extent and hence it will be comfortable to stay in the tent.

No, during winter it would be better to prefer the black tent because dark colours being good absorbers of heat falling on them will absorb maximum amount of heat they will receive and will keep the tent warm.

Question 4.
What is heat? How is it transferred from one body to other body? Explain various methods.
Answer:
Heat is the form of energy which causes sensation of hotness or the coolness. Heat is transferred from hotter body to colder body till the temperature becomes same. There are following three ways of the transfer of heat.

1. Conduction: The process by which heat is transferred from hot end of the object to the cold end of an object, is called conduction.
2. Convection: The process in the particles comes into contact of source of heat and become hot than others. The hot particles rise up and cold particles take their place. This process continues till the whole body gets heated is called convection.
3. Radiation: The process of transfer of heat in which transfer of heat does not require any medium is called radiation. It can take place whether a medium is present or not.

Question 5.
Explain the water cycle in detail.
Answer:
The water cycle is the process of continuous movement of water on Earth. It plays a very important role in supporting life by recycling and distributing water across the planet. The water keeps changing its form liquid, vapour, and sometimes solid and moves through different parts of the environment. The main processes involved in the water cycle are:

1. Evaporation: It is the process where water changes into vapour and rises into the atmosphere due to heat. This usually happens from oceans, rivers, lakes and other water bodies when the Sun shines on them.
2. Transpiration: It is the process where water is absorbed by plants from the soil and then released as water vapour through their leaves into the atmosphere. Together with evaporation, it adds moisture to the air.
3. Condensation: It is the process where water vapour cools down and changes back into liquid water, forming clouds in the sky.
4. Precipitation: It is the process when the water falls from the clouds to the Earth’s surface as rain, snow, or hail.
5. Infiltration: After precipitation, some water seeps into the ground and gets stored as groundwater. This process is called infiltration.

Heat Transfer in Nature Class 7 Skill-Based Questions

Question 1.
Draw a diagram to show the radiation by the sun.
Answer:

Fig. When any radiation falls on an object a part of it is reflected, a part is absorbed and a part may be transmitted.

Question 2.
Draw a diagram to show the conduction.
Answer:

Fig. Flow of heat through a metal strip.

Question 3.
Draw a diagram to show the convection.
Answer:

Fig. Convection of heat in water.

Heat Transfer in Nature Class 7 Case Based Questions

I. One winter morning, Priya made a cup of hot tea and placed the metal spoon inside it. She held the cup in her hands to feel warm. After a few minutes, she noticed the metal spoon had become hot. Then, she placed the cup on the table near the window where sunlight was coming in. She felt warm standing in the sunlight even without touching anything. Later, she saw the steam rising from the tea and disappearing into the air.
1. Why did the metal spoon become hot?
Answer:
The metal spoon became hot because of conduction. Heat transferred from the hot tea to the spoon through direct contact.

2. How did Priya feel warm just by standing in the sunlight?
Answer:
Priya felt warm standing in the sunlight due to radiation. Heat travelled from the Sun and reaches the Earth through radiation and warmed her directly.

3. What is the process called when hot steam rises from the tea?
Answer:
The hot steam rising from the tea shows convection. Hot air or steam rises and cooler air takes its place.
OR
Which modes of heat transfer are discussed in this case?
Answer:
The modes of heat transfer discussed are conduction, convection and radiation.

Heat Transfer in Nature Class 7 Suggested Projects and Activities

1. Take a sheet of paper. Draw a spiral on it as shown in the Fig. Cut out the paper along the line. Suspend the paper as shown in Fig. above a lighted candle. Observe what happens. Think of an explanation.

Fig.(a) Cutting paper (b)Spiral paper in spiral above a burning candle

2. Take two similar transparent glass bottles having wide mouths. Put a few crystals of potassium permanganate or pour a few drops of ink into 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 postcard 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 someone else to pull the postcard. Observe what happens. Explain.

Heat Transfer in Nature Extra Questions for Practice

Question 1.
Which of the following is a good conductor of heat?
(a) Wood
(b) Plastic
(c) Iron
(d) Rubber

Question 2.
Heat is transferred in liquids and gases mainly by:
(a) Conduction
(b) Convection
(c) Radiation
(d) Reflection

Question 3.
During daytime, a sea breeze blows because:
(a) The land cools faster than the sea
(b) The sea heats up faster than the land
(c) The land heats up faster than the sea
(d) The temperature of both is equal

Question 4.
Read the given statements and select the correct option.
Assertion (A): Radiation requires a medium for heat transfer.
Reason (R): Radiation can travel through empty space.
(a) Both A and R are true and R is the correct explanation of A.
(fa) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

Question 5.
Match the items in Column A with those in Column B.

(a) (i) – (s), (ii) – (r), (iii) – (p), (iv) – (q)
(b) (i) – (p), (ii) – (q), (iii) – (s), (iv) – (r)
(c) (i) – (r), (ii) – (q), (iii) – (p), (iv) – (s)
(d) (i) – (q), (ii) – (p), (iii) – (s), (iv) – (r)

Question 6.
Name the method of heat transfer in solids.

Question 7.
Name one poor conductor of heat.

Question 8.
Name one process that increases the groundwater level.

Question 9.
What is the process of water loss from plant leaves called?

Question 10.
Do all objects radiate heat?

Question 11.
What are sea the sea and the land breeze?

Question 12.
Define the terms conductor and insulator.

Question 13.
State two ways in which water returns to the Earth’s surface in the water cycle.

Question 14.
What is an aquifer?

Question 15.
Why do concrete surfaces reduce seepage of water into the Earth?

Question 16.
Explain the principle of heat transfer used in designing houses in hot regions.

Question 17.
How does the structure of sand and clay affect water seepage?

Question 18.
How does the water cycle help in maintaining a sustainable supply of water?

Question 19.
Differentiate between conduction, convection and radiation.

Question 20.
Draw a diagram to show convection of heat in water.

Question 21.
In a thermos flask, hot tea remains hot. How is the loss of heat prevented from the thermos flask?

Question 22.
How do conduction, convection and radiation occur in daily life? Give one example for each.

Question 23.
Describe the complete water cycle with all its major processes.

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