Reviewing the Curiosity Class 7 Science Book Solutions Chapter 7 Heat Transfer in Nature Class 7 Question and Answer before exams can boost your confidence.
Class 7 Science Chapter 7 Heat Transfer in Nature Question Answer
Science Class 7 Chapter 6 Question Answer Heat Transfer in Nature
Heat Transfer in Nature Class 7 Question Answer (InText)
Question 1.
Why is the smoke going up? (Page 92)
Answer:
The smoke rises because of convection. When a fire heats the air, the hot air becomes less dense and rises. As it moves upward, it carries the smoke with it. Cooler air then sinks to replace the rising hot air, creating a continuous cycle that keeps the smoke moving upward.
Question 2.
How does heat transfer take place in liquids ? Do liquids also rise up when heated like air? (Page 93)
Answer:
In liquids, heat transfer occurs through convection. When a liquid is heated, its particles move faster, becomes less dense, and rises. The cooler, denser liquid sinks to replace the rising hot liquid, creating a convection current that spreads heat throughout the liquid.
Question 3.
How does water seep through the surface of the earth? (Page 99)
Answer:
Water seeps into the Earth through infiltration when it rains. It moves through the gaps between soil particles and continues downward due to gravity. This process, called percolation, helps water to reach underground water sources like aquifers.
NCERT Class 7 Science Chapter 7 Question Answer Heat Transfer in Nature (Exercise)
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 figure below.
The materials A and B have the following properties:
(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.
Answer:
(c) A is a good conductor and B is a poor conductor of heat because
A (the pan body) conducts heat well to cook food, so it’s a good conductor.
B (the handle) does not get heat easily, so it’s a poor conductor for safe handling.
Question 2.
Pins are stuck to a metal strip with wax and a burning candle is kept below the rod, as shown in figure below.
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.
Answer:
(d) When the metal strip is heated, heat transfer to the ends of the rod through conduction. Since, pins II and III are located closest and at the same distance to the candle, so their wax melts simultaneously and both will fall at the same time.
Question 3.
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:
(c) On the ceiling Hot air and smoke rise up due to convection, so the ceiling is the best place to detect smoke early.
Question 4.
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, this arrangement will help to keep the lassi cold for a longer time.
- The second tumbler acts as an insulating layer, reducing heat transfer from the surroundings to the cold lassi. This slows down warming and keeps the lassi cold for a longer period.
Question 5.
State with reason(s) whether the following statements are True [T] or False [F].
(i) Heat transfer takes place in solids through convection.
(ii) Heat transfer through convection takes place by the actual movement of particles.
(iii) Areas with clay materials allow more seepage of water than those with sandy materials.
(iv) The movement of cooler air from land to sea is called land breeze.
Answer:
(i) False [F]
Reason: Convection does not occur in solids; it occurs in liquids and gases. Solids transfer heat mainly by conduction.
(ii) True [T]
Reason: In convection, heat is transferred by the actual movement of particles in liquids or gases.
(iii) False [F]
Reason: Sandy materials allow more seepage of water than clay, because sand has larger pores.
(iv) True [T]
Reason: At night, land cools faster than sea. Cooler air from land moves towards the sea. This is called land breeze.
Question 6.
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 get heat from the surrounding air and the dish, which are at a higher temperature. This heat causes the ice to melt into water.
Question 7.
Two test tubes with water are heated by a candle flame as shown in figure. Which thermometers (Fig. a or Fig. b) will record a higher temperature? Explain.
Answer:
In the experiment shown in figure, thermometer in Fig. (b) will record a higher temperature than the one in Fig. (a). This is because in Fig. (b) thermometer is positioned closer to the candle flame, allowing it to absorb more heat and reach a higher temperature more quickly.
Question 8.
Why are hollow bricks used to construct the outer walls of houses in hot regions?
Answer:
Hollow bricks trap air inside them, and air is a poor conductor of heat. This reduces the transfer of heat from outside to inside, helping to keep the house cool in hot regions.
Question 9.
Explain how large water bodies prevent extreme temperature in areas around them.
Answer:
Large water bodies absorb heat slowly during the day and release it slowly at night. This moderates the temperature of nearby areas, preventing them from becoming too hot during the day or too cold at night.
Question 10.
Explain how water seeps through the surface of the Earth and gets stored as groundwater.
Answer:
When it rains, some of the water flows over the surface, but some seeps through soil and rocks due to gravity. This water passes through pores in sandy layers and gets collected in underground spaces, forming groundwater.
Question 11.
The water cycle helps in the redistribution and replenishment of water on the Earth. Justify the statement.
Answer:
The water cycle moves water through evaporation, condensation, precipitation, and infiltration. This natural cycle helps to redistribute water from oceans to land and back, and it replenishes groundwater and surface water sources, making water available for plants, animals, and humans.
Class 7 Heat Transfer in Nature Question Answer (Activities)
Activity 1 (page 90)
Aim To observe the transfer of heat through a metal strip and understand that heat travels from the hotter end to the colder end by conduction.
Material Required
- Metal strip (iron or aluminium), about 15 cm long
- 4 small pins
- Candle or spirit lamp
- Wax
- Stand or two bricks for support
- Matchstick or lighter
- Forceps (for safety)
Procedure
- Take a metal strip and attach four pins (I, II, III, IV) on it using small blobs of wax, keeping them about 2 cm apart.
- Fix the metal strip to a stand vertically or place it horizontally between two bricks so it remains steady.
- Label the pins such that Pin IV is closest to the free end (the end that will be heated), and Pin I is closest to the stand or support as shown in figure.
- Using a candle or spirit lamp, gently heat the free end (near Pin IV) of the metal strip.
- Carefully observe which pins fall off and in what order, as the wax melts.
Observation
| Position from Heated End | Did it Fall? | Order of Falling |
| Nearest | Yes | 1st |
| Yes | 2rd | |
| Yes | 3rd | |
| Farthest | Yes | 4th |
Conclusion:
• Heat travels through the metal strip from the hot end to the cold end.
• The pins fall one by one in the direction of heat flow, proving that metals are good conductors of heat.
• The closer the pin to the heat source, the sooner it falls.
Viva Questions
1. Why do metals conduct heat better than wood or plastic?
2. If the strip were made of plastic, what would happen?
3. Why do we heat the free end of the strip and not the end near the stand?
4. What kind of heat transfer is shown in this activity?
5. What safety precaution should be taken during this activity?
Activity 2 (Page 92)
Aim To observe the movement caused by heating air and understand that hot air rises, affecting balance.
Materials Required
• 2 identical paper cups
• Wooden stick or scale
• Thread (2 equal lengths)
• Candle or spirit lamp
• Matchbox
• Stand (or a clamp setup)
Procedure
- Take two identical paper cups and hang them in inverted position using equal-length threads from both ends of a wooden stick.
- Ensure that the stick is balanced horizontally, forming a simple beam balance (Fig. a).
- Light a candle and place it under one of the inverted cups (Fig. b).
- Observe what happens to the cup abipve the flame after a few seconds or minutes.
- Record your observations in Table.
Observation
| Initial Setup | Change Observed | Probable Reason |
| Both cups balanced | The cup above the flame starts moving or tipping | Hot air rises, reducing air pressure or burning the cup, causing imbalance |
Conclusion:
• Hot air rises when a candle is placed under the inverted cup.
• The rising hot air causes movement or imbalance in the setup.
• This activity shows that air expands and becomes lighter when heated.
Viva Questions
1. Why did we use paper cups instead of plastic cups?
2. What happens to air when it is heated?
3. Why did the balance tilt or move when a candle was placed under a cup?
4. If we used metal cups, would the result be the same? Why or why not?
5. What property of air is demonstrated in this activity?
6. How does this relate to real-life examples?
Activity 3 (Page 93)
Aim To observe the movement of water due to heat and demonstrate that heat is transferred in liquids by convection.
Material Required
• 500 mL beaker
• Water (about 250 mL)
• Potassium permanganate crystals (or food colour as an alternative)
• Straw (for precise placement)
• Candle
• Matchstick
• Tripod stand or stable support
• Adult supervision
Procedure
- Take a 500mL glass beaker and half-fill it with water.
- Using a straw, gently place a small grain of potassium permanganate (or drop of food colour) at the centre of the beaker’s base (Fig. a).
- Place the beaker carefully on a tripod stand, or hold it steadily.
- Light a candle and place it just below the base of the beaker, exactly under the coloured grain.
- Do not stir the water. Let it remain still and observe carefully.
- Watch for the movement of the coloured streak inside the water (Fig. b).
- Record your observations.
Observation
| Initial Setup | Change Observed | Probable Reason |
| Colour is at the bottom centre | Colour rises in a streak and spreads, then moves down from the sides | Water gets heated at the bottom, becomes lighter and rises, cooler water from the sides moves down to replace it. This is convection. |
Conclusion:
• The coloured water moves upward from the heated centre and downward along the sides, forming a convection current.
• Heat is transferred in water by the actual movement of water particles this is called convection.
• This experiment shows that liquids, like water, get heated through convection currents.
Viva Questions
1. Why does the coloured water move upward in the centre?
2. What causes the water at the sides to move downward?
3. What is the name of this heat transfer process?
4. How is convection different from conduction?
5. Why is potassium permanganate used in this activity?
Activity 4 (Page 94)
Aim To compare how soil and water heat up when exposed to sunlight and to understand which one heats faster.
Material Required
• 2 identical bowls
• Soil (to fill one bowl halfway)
• Water (to fill the second bowl halfway)
• 2 laboratory thermometers
• Stopwatch or clock
• Sunny location
• Teacher/adult supervision
Procedure
- Take two identical bowls as shown in figure.
- Fill one bowl half-way with soil, and the other half-way with water.
- Insert a laboratory thermometer in each bowl such that the bulb is fully immersed (in soil and in water), but not touching the bottom or sides as shown in figure.
- Place both bowls in direct sunlight at the same time.
- Record the temperatures shown by each thermometer at 0, 5,10,15, and 20 minutes.
- Record your readings in Table below.
| Time (min) | Temperature of soil (°C) | Temperature of water (°C) |
| 0 | 25 | 25 |
| 5 | 28 | 26 |
| 10 | 31 | 27 |
| 15 | 34 | 28 |
| 20 | 36 | 29 |
Observation
• The temperature of soil increases faster than that of water.
• After 20 minutes, soil is significantly hotter than water.
Conclusion:
• Soil heats up faster than water when exposed to sunlight.
• This happens because water requires more heat to raise its temperature compared to soil.
• As a result, in nature, land gets heated and cools quickly, whereas water gets heated and cools slowly.
Viva Questions
1. Which bowl showed a higher temperature after 20 minutes? Why?
2. In nature, which heats up faster during the day-land or sea?
3. Why do coastal areas have more stable temperatures?
4. If this setup was placed in shade, would there be much difference in temperature?
5. Does soil also cool down faster than water?
Activity 5 (Page 99)
Aim To compare how water seeps through clay, sand, and gravel, and understand which type of soil allows water to pass through more easily.
Materials Required
• 3 transparent used 1-litre plastic botdes
• Sharp tool or scissors (to cut bottles and make holes)
• Clay, sand, and gravel
• 3 identical beakers
• Measuring cylinder (to measure 200 mL water)
• Stopwatch or clock
• Water (600 mL total)
• Supervision by a teacher or adult
Procedure
1. Take three 1-litre plastic bottles and cut each bottle in the middle.
2. Make a small hole in the cap of each bottle.
3. Invert the bottles so the cap faces down as shown in figure.
4. Fill:
• First bottle with clay
• Second bottle with sand
• Third bottle with gravel
5. Place a beaker below each bottle to collect seeping water.
6. Pour 200mL of water into the top of each bottle simultaneously.
7. Let the setup sit undisturbed for 10 minutes.
8. Measure the amount of water collected in each beaker.
9. Record your observations in Table
| Type of Material | Water Added (mL) | Water Collected After 10 min (mL) |
| Clay | 200 | 40 |
| Sand | 200 | 120 |
| Gravel | 200 | 180 |
Observation
• Gravel allowed the most water to pass through.
• Sand allowed moderate seepage.
• Clay allowed the least water to pass through, absorbing and holding most of it.
Conclusion:
• Porosity and particle size affect the rate at which water seeps through soil.
• Gravel, with large spaces between particles, allows maximum seepage.
• Clay, with very fine and compact particles, retains water and allows minimum seepage.
• This explains why different soils have different water-holding capacities.
Viva Questions
1. Which type of material allowed the most water to pass through? Why?
2. Why does clay hold more water ?
3. Which soil is better for growing crops requiring more water?
4. Why is sandy soil used for quick drainage areas ?