Heat Transfer in Nature - Class 7 New NCERT Solution

Heat Transfer in Nature - New NCERT Exercise Solutions

Q1. 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. The correct option is (c).

A is a good conductor of heat 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. The correct option is (b).
Pins I and II will fall earlier than pins III and IV. Because, the heat always flow from hotter side to colder side. 

(iii) A smoke detector is a device that detects smoke and sounds an alarm. Suppose you are fi tting a smoke detector in your room. The most suitable place for this device will be:

(a) Near the fl oor

(b) In the middle of a wall

(c) On the ceiling

(d) Anywhere in the room

Ans. The correct option is (c) On the ceiling.

Smoke rises upward, so smoke detectors are fixed 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.

Air gets trapped between the two tumblers. Air is a poor conductor of heat, so less heat reaches the lassi.

3. 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. 

Ans. 

(i) False
(ii) True
(iii) False
(iv) True

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 surroundings like air, dish and nearby objects. This heat melts the ice into water.

5. A burning incense stick is fi xed, pointing downwards. In which direction would the smoke from the incense stick move? Show the movement of smoke with a diagram.

Ans. The smoke will first move downward and then rise upward. Hot smoke becomes lighter and rises due to convection currents.

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 this figure, the flame heats the water from below. Hot water rises upward and heats the thermometer more quickly.

7. Why are hollow bricks used to construct the outer walls of houses in hot regions?

Ans. Hollow bricks contain air spaces. Air is a poor conductor of heat, so less heat enters the house.

8. Explain how large water bodies prevent extreme temperature in areas around them.

Ans. Large water bodies heat up and cool down slowly as compare to the land. Sand is better conductor of heat so it heats up faster. It also cool down faster as well. Areas nearby land becomes too hot in the day and too cold in the night. Water being a poorer conductor do not heat up fast. So, areas nearby water bodies do not become very hot in summer or very cold in winter.

9. Explain how water seeps through the surface of the Earth and gets stored as groundwater.

Ans. Water enters the soil through small spaces between soil particles. This process is called seepage. The water moves downward and gets stored as groundwater.

10. The water cycle helps in the redistribution and replenishment of water on the Earth. Justify the statement.

Ans. Water cycle changes water from one form to another and moves it from one place to another. It brings rain and refills rivers, lakes and groundwater. Thus, water gets redistributed and replenished on Earth. 

Also see : Class 7 Science All Chapter's NCERT Solutions