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

Students can use Curiosity Class 7 Science Book Solutions Chapter 7 Heat Transfer in Nature Class 7 Question and Answer as a quick reference guide.

Class 7 Science Chapter 7 Heat Transfer in Nature Question Answer

Science Class 7 Chapter 7 Question Answer Heat Transfer in Nature

Heat Transfer in Nature Class 7 Question Answer (InText)

Question 1.
If we use a strip made of a material like wood or glass in place of a metal strip to perform activity 7.1, the pins will not fall. Can you think of the reason for this based on our learning from the chapter ‘The World of Metals and Non-Metals’? (Page 91)
Answer:
If we use a strip made of wood or glass, the pins will not fall because wood and glass are poor conductors of heat. They do not allow heat to pass through them easily, so the heat will not reach the wax to melt it. Thus, the pins will remain attached to the strip.

Question 2.
List some materials around you and classify them as good or poor conductors of heat in Table 7.2.
Table 7.2: List of good or poor conductors of heat

Material	Good or poor conductor of heat
Steel	Good conductor
Wood

Does your list include air? If it is there on the list, where have you placed it?

Material	Good or poor conductor of heat
Steel	Good conductor
Wood	Poor conductor
Air	Poor conductor
Copper	Good conductor
Glass	Poor conductor
Aluminum	Good conductor
Plastic	Poor conductor
Iron	Good conductor
Rubber	Poor conductor
Water	Poor conductor

Air is a poor conductor of heat, that is why woollen clothes keep us warm by trapping air.

NCERT Class 7 Science Chapter 7 Question Answer Heat Transfer in Nature (Exercise)

Let us Enhance Our Learning (Pages 102-104)

Question 1.
Choose the correct option in each case.
(i) Your father bought a saucepan made of two different materials, A and B, as shown in Fig. 7.14. The materials A and B have the following properties

Fig. Saucepan

(a) Both A and B are good conductors of heat
(b) Both A and B are poor conductors of heat
(c) A is a good conductor and B is a poor conductor of heat
(d) A is a poor conductor and B is a good conductor of heat

(ii) Pins are stuck to a metal strip with wax and a burning candle is kept below the rod, as shown in Fig. 7.15. Which of the
following will happen?
(a) All the pins will fall almost at the same time
(b) Pins I and II will fall earlier than pins III and IV
(c) Pins I and II will fall later than pins III and IV
(d) Pins II and III will fall almost at the same time

Fig. Transfer set-up

(iii) A smoke detector is a device that detects smoke and sounds an alarm. Suppose you are fitting a smoke detector in your room. The most suitable place for this device will be:
(a) Near the floor
(b) In the middle of a wall
(c) On the ceiling
(d) Anywhere in the room
Answer:
(i) (c) A is a good conductor and B is a poor conductor of heat
(ii) (d) Pins II and III will fall almost at the same time
(iii) (c) On the ceiling

Question 2.
A shopkeeper serves you cold lassi in a tumbler. By chance, the tumbler had a small leak. You were given another tumbler by the shopkeeper to put the leaky tumbler in it. Will this arrangement help to keep the lassi cold for a longer time? Explain.
Answer:
Yes, the arrangement will keep the lassi cold for a longer time. The air trapped between the two tumblers acts as an insulator since air is a poor conductor of heat. It reduces the transfer of heat from the surroundings to the lassi, helping it stay cool for a longer period.

Question 3.
State with reason(s) whether the following statements are True [T] or False [F],
(i) Heat transfer takes place in solids through convection.
Answer:
False, heat transfer takes place in solids through conduction.

(ii) False, heat transfer takes place in solids through conduction. Heat transfer through convection takes place by the actual movement of particles.
Answer:
True

(iii) Areas with clay materials allow more seepage of water than those with sandy materials.
Answer:
False, areas with particles of gravel allow more seepage of water as the space or pores between the particles of gravel is more as compared to sandy materials.

(iv) The movement of cooler air from land to sea is called land breeze.
Answer:
True

Question 4.
Some ice cubes placed in a dish melt into water after sometime. Where do the ice cubes get heat for this transformation?
Answer:
The ice cubes absorb heat from their surroundings, including the air and the surface they are placed on. This heat causes the ice to melt, changing it from a solid state to a liquid state, turning it into water.

Question 5.
A burning incense stick is fixed, pointing downwards. In which direction would the smoke from the incense stick move? Show the movement of smoke with a diagram.
Answer:
The smoke from the incense stick will move in the upward direction because smoke is a mixture of hot gases and tiny solid particles. Since hot air rises due to convection, the smoke moves upwards.

Question 6.
Two test tubes with water are heated by a candle flame as shown in Fig. 7.16. Which thermometers (Fig. 7.16 a or Fig. 7.16 b) will record a higher temperature? Explain.

Fig. Two thermometers dipped in two test tubes
Answer:
In Fig. (a), the thermometer is placed at the top of the test tube and candle flame heats the bottom of the test tube directly. The water at the bottom gets heated first. As the water heats up, it rises due to convection, carrying heat to the top, where the thermometer is placed. So, the thermometer quickly records a temperature rise.

In Fig. (b), the thermometer is placed at the bottom of the test tube, but the candle flame heats the side of the test tube. The side heating may not be as effective in transferring heat to the bottom where the thermometer is placed. Therefore, the thermometer in Fig. (a) will record a higher temperature.

Question 7.
Why are hollow bricks used to construct the outer walls of houses in hot regions?
Answer:
The air gets trapped in the hollow bricks and air is a poor conductor of heat. This trapped air acts as an insulator and prevent the heat from entering the house, keeping the interior cooler.

Question 8.
Explain how large water bodies prevent extreme temperature in areas around them.
Answer:
Large water bodies like seas and oceans prevent extreme conditions in areas around them. In coastal areas during day, the land heats up faster than water, so cooler air from the sea flows towards the land (sea breeze), keeping the temperature moderate. At night, land cools down faster than water. The air above the sea remains warmer, while the cooler air from the land moves towards the sea (land breeze). This movement of air helps prevent extreme temperatures in coastal regions.

Fig. (a) Sea breeze (b) Land Breeza

Question 9.
Explain how water seeps through the surface of the Earth and gets stored as groundwater.
Answer:
Water seeps through the surface of the Earth by gradually passing through the soil and porous rocks. This process is known as infiltration. This water fills the pores and cracks in rocks and soil and gets stored underground as groundwater. The layers of sediments and rocks that store water in their pore spaces are known as aquifers.

Question 10.
The water cycle helps in the redistribution and replenishment of water on the Earth. Justify the statement.
Answer:
The water cycle helps in the continuous redistribution and replenishment of water on Earth through the movement of water in different stages, such as evaporation, condensation and precipitation. Water from oceans, rivers and lakes evaporates due to the Sun’s heat, forms clouds through condensation, and falls back to Earth as rain or snow through a process called precipitation. The rain refills lakes, rivers and groundwater, ensuring the continuous availability of water on Earth.

Class 7 Heat Transfer in Nature Question Answer (Activities)

Activity 7.1: Let Us Experiment (Pages 90-91)

Caution – This activity should be carried out under the supervision of a teacher or an adult.

1. Take a strip of a metal, such as aluminium or iron, about 15 cm long.
2. Attach four pins to the strip with the help of wax such that they are arranged at nearly equal distances (about 2 cm apart), as shown in Fig. 7.1.
3. Secure the strip to a stand and label the pins as I, II, III, and IV, as shown in Fig. 7.1. (If a stand is not available, place the strip between two bricks for support.)
4. Heat the end of the strip that is away from the stand with a candle or a spirit lamp.
5. What will happen to the pins? Will they remain attached to the strip or will they fall?
6. Predict the order in which the pins will fall from the strip.
7. Record your observations in Table 7.1.

Pin falling first		Reasons for what you observed
Prediction	Observation

You observed that the pin closest to the candle flame (Pin I falls first, followed by pins II, III, and IV. Why does pin I fall before pin II? Why did all the pins not fall together?
Answer:
Table 7.1

Pin falling first	Pin I: Will fall together with other pins	Pin I fell first	Reasons for what you observed
Ist (Pin I)	Pin II: Will fall together with other pins	Pin II fell second	Pin I is close to the flame, so it gets heated first. Wax melts and pin falls.
2nd (Pin II)	Pin III: Will fall together with other pins	Pin III fell third	After pin I falls, heat reaches, pin II next, melting its wax.
3rd (Pin III)	Pin IV: Will fall together with other pins	Pin IV fell last	Heat continues to travel along the metal strip to pin III.
4th (Pin IV)	Pin I: Will fall together with other pins	Pin I fell first	Pin IV is farthest from the flame; it gets heated last.

Pin I falls before Pin II because it is closer to the flame and gets heated first. As heat travels through the metal strip by conduction, it takes time for the heat to reach the pins farther away. All the pins do not fall together because heat moves gradually from the hot end to the colder end of the strip. Each pin falls only after the wax holding it melts due to the heat.

Activity 7.2: Let Us Investigate (Pages 92-93)

1. Take two identical paper cups.
2. Hang them using threads of equal length in an inverted position on the two ends of a wooden stick, as shown in Fig. a.
3. Now, adjust the positions of the cups, so that the stick is horizontal.
4. Place a burning candle below one of the cups (Fig. b).
5. Observe what happens to the cup.
6. Record your observations in Table and think of probable reasons.

Fig. (a): Initial set-up (b): Hot air rising up

Table 7.3: Recording observations and probable reasons

Observation about the cups	Probable reasons for the observation

Answer:

Observation about the cups	Probable reasons for the observation
The cup above the burning candle rises up.	The air under the cup gets heated, becomes lighter, and rises, lifting the cup.

Activity 7.4: Let Us Investigate (Pages 94-95)

Caution-This activity should be carried out on a clear, sunny day under the supervision of a teacher or an adult.

1. Take two identical bowls as shown in Fig. 7.6. (See NCERT TB)
2. Fill one bowl halfway with soil and the other bowl halfway with water.
3. Fix a laboratory thermometer in each bowl as shown in Fig. 7.6. Make sure that the bulbs of the thermometer are immersed in soil and water, and do not touch the bottoms or the sides of the bowls.
4. Place the set-up in sunlight.
5. Measure the temperature of soil and water every 5 minutes and record the data in Table 7.4.

Table 7.4: Temperature of soil and water when heated

Time(min)	Temperature of soil (°C)	Temperature of water (°C)
0
5
10
15
20

• Study the rise in temperature of soil and water.
• Did the temperature rise by the same amount for both the soil and the water at the same time?
• If not, which one got heated faster?
• How much was the rise in temperature of the soil and the water in 20 minutes?
Answer:

Time(min)	Temperature of soil (°C)	Temperature of water (°C)
0	25	25
5	27	26
10	29	27
15	32	28
20	35	29

• No, the soil’s temperature rose faster than the water’s.
• Soil got heated faster.
• Soil: 35°C — 25°C = 10°C rise
Water: 29°C — 25°C 4°C rise

Activity 7.5: Let Us Investigate (Page 99)

1. Take three transparent, used plastic bottles of 1 L capacity.
2. Cut them in the middle and make a small hole in the cap of each bottle.
3. Keep them inverted and put some clay in one bottle, sand in the second, and gravel in the third, as shown in Fig. 7.10
4. Place three identical beakers below each bottle.
5. Add 200 mL of water to each bottle.
6. Predict the amount of water flowing out of each bottle.
7. Collect the water that flows through each bottle for 10 minutes.

Table 7.5: Seepage of water

Bottles filled with	Prediction	Observation
	Seepage of water (very slow/slow/fast)	Seepage of water (very slow/slow/fast)
Bottle 1 (Clay)	Very slow	Very slow
Bottle 2 (Sand)	Slow	Slow
Bottle 3 (Gravel)	Fast	Fast