NCERT Class 7 Science Chapter 7 Heat Transfer in Nature Solutions to each chapter is provided in the list so that you can easily browse through different chapters NCERT Class 7 Science Chapter 7 Heat Transfer in Nature and select need one. NCERT Class 7 Science Chapter 7 Heat Transfer in Nature Question Answers Download PDF. NCERT Class 7 Science Solutions.
NCERT Class 7 Science Chapter 7 Heat Transfer in Nature
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Heat Transfer in Nature
Chapter: 7
Page No – 90
Table 7.1: Falling of pins.
| Pin falling first | Reasons for what you observed | |
| Prediction | Observation | . |
Ans:
| Pin falling first | Reasons for what you observed | |
| Prediction | Observation | In the absences of significance air resistances all abject fall at the same rate due to gravity. |
| Metal pin will fall first | Both pins fell at the same time | |
Page No – 91
Table 7.2: List of good or poor conductors of heat.
| S.No. | Material | Good or Poor conductor of heat |
| 1. | Steel | Good conductor |
| 2. | Wood | |
| 3. |
Ans:
| S.No. | Material | Good or Poor conductor of heat |
| 1. | Steel | Good conductor |
| 2. | Wood | Poor conductor |
| 3. | Copper | Good conductor |
Page No – 93
Table 7.3: Recording observations and probable reasons.
| Observation about the cups | Probable reasons for the observation |
Ans:
| Observation about the cups | Probable reasons for the observation |
| Water in metal cup cooler faster than in plastic cup | Metal is a good conductor of heat, plastic is a poor conductor |
Page No – 95
Table 7.4: Temperature of soil and water when heated.
| S.No. | Time (min) | Temperature of soil (°C) | Temperature of water (°C) |
| 1 | 0 | ||
| 2 | 5 | ||
| 3 | 10 | ||
| 4 | 15 | ||
| 5 | 20 |
Ans:
| S.No. | Time (min) | Temperature of soil (°C) | Temperature of water (°C) |
| 1 | 0 | 25 | 25 |
| 2 | 5 | 35 | 30 |
| 3 | 10 | 45 | 34 |
| 4 | 15 | 53 | 37 |
| 5 | 20 | 60 | 40 |
Page No – 99
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) | ||
| Bottle 2 (Sand) | ||
| Bottle 3 (Gravel) |
Ans:
| 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 |
| Let Us Enhance Our Learning |
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 —
(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.
Ans: (c) A is a good conductor and B is a poor 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.
Ans: (b) Pins I and II will fall earlier than pins III and IV.
(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.
Ans: (c) On the ceiling.
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.
Ans: Yes, this arrangement will help to keep the lassi cold for a longer time.When the leaky tumbler is placed inside another tumbler, a layer of air gets trapped between the two. Air is a poor conductor of heat (a good insulator), so it reduces the transfer of heat from the outside environment to the cold lassi. The second tumbler prevents the lassi from spilling due to the leak, making it a practical solution both for insulation and cleanliness.
3. State with reason(s) whether the following statements are True [T] or False [F].
(i) Heat transfer takes place in solids through convection. [ ]
Ans: False.
Reason: Convection requires the movement of particles, which is not possible in solids. In solids, heat is transferred mainly through conduction.
(ii) Heat transfer through convection takes place by the actual movement of particles. [ ]
Ans: True.
Reason: In convection, heat is transferred by the movement of fluid particles (liquids or gases), carrying heat from one place to another.
(iii) Areas with clay materials allow more seepage of water than those with sandy materials. [ ]
Ans: False.
Reason: Clay has very fine particles and low permeability, so it holds water rather than letting it seep. Sandy soil has larger particles, allowing more seepage.
(iv) The movement of cooler air from land to sea is called land breeze. [ ]
Ans: True.
Reason: At night, land cools faster than the sea, so cooler air from the land moves towards the sea, forming a land breeze.
4. Some ice cubes placed in a dish melt into water after sometime. Where do the ice cubes get heat for this transformation?
Ans: The ice cubes get heat from the surrounding environment, primarily from the air and the dish they are placed in. The heat energy causes the ice cubes to absorb thermal energy, which increases the temperature of the ice and leads to its melting, transforming it into water.Since the air and the dish are warmer than the ice, the heat flows into the ice, making it melt into water.
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.
Ans: When an incense stick is burning and fixed pointing downwards, the smoke will move upward. This happens because the hot air and smoke from the incense are lighter than the cooler surrounding air, causing them to rise due to convection.
6. Two test tubes with water are heated by a candle flame as shown in Fig. 7.16. Which thermometers (Fig. 7.16a or Fig. 7.16b) will record a higher temperature? Explain.
Ans: The thermometer in Fig. 7.16(b) will record a higher temperature.
In Fig. 7.16(b), the flame directly heats the water at the bottom of the test tube, where the thermometer bulb is located. This allows the heat to be transferred efficiently to the water and then to the thermometer, causing a rise in temperature.on the other hand in Fig. 7.16(a), the flame heats the upper part of the test tube, where there is little or no water. Heat transfer to the thermometer (which is lower down) is less efficient, so the temperature reading will be lower.
7. Why are hollow bricks used to construct the outer walls of houses in hot regions?
Ans: Hollow bricks used to construct the outer walls of houses in hot regions because hollow bricks that keep them warm in winters and cool in summers. This happens because the air that gets trapped in the hollow bricks is a poor conductor of heat.
8. Explain how large water bodies prevent extreme temperature in areas around them.
Ans: Large water bodies help keep the temperature steady in nearby areas. During the day, water heats up slowly, so it keeps the air cooler. At night, it gives off the heat slowly, so the air doesn’t get too cold. This way, places near oceans or lakes don’t get too hot in summer or too cold in winter. The temperature stays more balanced throughout the year.
9. Explain how water seeps through the surface of the Earth and gets stored as groundwater.
Ans: Water seeps through the surface of the Earth by a process called infiltration. When it rains, water moves through the spaces between soil and rock particles. This happens more easily when the spaces are wider and well connected, like in gravel. As the water goes deeper, it gets stored in the pore spaces of sediments and in the openings in rocks beneath the surface. These water-holding layers are called aquifers. Groundwater is stored in these aquifers and can be extracted by digging wells or drilling bore wells.
10. The water cycle helps in the redistribution and replenishment of water on the Earth. Justify the statement.
Ans: The water cycle moves water around the Earth and helps refill it in different places. When the Sun heats up water from rivers, lakes, or oceans, it turns into vapor and goes up into the sky. This vapor forms clouds, and later comes back down as rain or snow. The rainwater fills rivers, lakes, and also goes into the ground to become groundwater. This whole process keeps water moving and makes sure places don’t run out of it.
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