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# NCERT Exemplar for Class 7 Science Solutions Chapter 4 Heat

Last updated date: 11th Aug 2024
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## NCERT Exemplar Solutions for Class 7 Science(Physics) Chapter 4 - Heat

### Multiple Choice Questions

1. A marble tile would feel cold as compared to a wooden tile on a winter morning because the marble tile

(a) Is a better conductor of heat than the wooden tile.

(b) Is polished while wooden tile is not polished.

(c) Reflects more heat than wooden tile.

(d) Is a poor conductor of heat than the wooden tile.

Ans:  The marble tile would be colder than the wooden tile because the marble tile is a better conductor of heat as compared to the wooden tile. Hence, the correct answer is option (a).

2. A beggar wrapped himself with a few layers of newspaper on a cold winter night. This helped him to keep himself warm because

(a) Friction between the layers of newspaper produces heat.

(b) Air trapped between the layers of newspaper is a bad conductor of heat.

(c) Newspaper is a conductor of heat.

(d) Newspaper is at a higher temperature than the temperature of the surrounding area.

Ans: The beggar kept himself warm because the air which is trapped between the layers of the newspaper is a bad conductor of heat. Therefore, the coldness doesn’t reach his body and he stays warm. Hence, the correct answer is option (b).

3. Paheli and Boojho measured their body temperature. Paheli found her’s to be 98.6 °F and Boojho recorded 37°C. Which of the following statements is true?

(a) Paheli has a higher body temperature than Boojho.

(b) Paheli has a lower body temperature than Boojho.

(c) Both have normal body temperature.

(d) Both are suffering from fever.

Ans: Paheli’s body temperature is measured in Fahrenheit, whereas Boojho’s body temperature has been measured in the Celsius units. If we convert 37°C into Fahrenheit units then it will be equal to 98.6 °F which is the ideal human body temperature. Hence, the correct answer is option (c).

4. Boojho has three thermometers as shown in Figure 4.1. He wants to measure the temperature of his body and that of boiling water. Which thermometer(s) should he choose?

(a) Thermometer (i) or (iii) for measuring body temperature and (ii) for measuring the temperature of boiling water.

(b) Thermometer (i) for measuring temperature of both.

(c) Thermometer (ii) for measuring temperature of both.

(d) Thermometer (iii) for measuring temperature of both.

Ans: Thermometer (i) or (iii) are used for measuring low temperatures such as the room or body temperature and (ii) for measuring higher temperatures such as of boiling water. Hence, the correct answer is option (a)

5. Four arrangements to measure temperature of ice in a beaker with laboratory thermometer are shown in Figure 4.2 (a, b, c and d). Which one of them shows the correct arrangement for accurate measurement of temperature?

Figure 4.2

Ans: In figure (a), the thermometer is placed in such a way that its lower end does not touch the bottom of the beaker and is immersed enough in ice. Hence, the correct answer is option (a).

6. Fig 4.3 (a–d) shows a student reading a doctor’s thermometer. Which of the figures indicate the correct method of reading temperature?

Ans: A thermometer should be handled from the top end keeping it horizontally straight and close to the eyes to measure an accurate reading. Hence, the correct answer is option (a).

7. Figure 4.4. (a–d) shows the readings on four different thermometers. Indicate which of the reading shows the normal human body temperature?

Ans: The ideal human body temperature is 37°C in the Celsius units. It is shown by the third  thermometer in the above figure. Hence, the correct answer is option (c).

### Very Short Answer Questions

8. Shopkeepers selling ice blocks usually cover them with jute sacks. Explain why.

Ans: Jute is a bad conductor of heat and it prevents the ice wrapped inside it from melting quickly. As a result, ice block sellers frequently wrap them in jute sacks. Newspapers, saw dust, etc are also used instead of jute to cover ice sometimes.

9. A laboratory thermometer A is kept 7 cm away on the side of the flame while a similar thermometer B is kept 7 cm above the flame of a candle as shown in Figure 4.5.

Which of the thermometers, A or B, will show a greater rise in temperature? Give reason for your answer.

Ans: The thermometer B will show a higher temperature than the thermometer A because the air above the candle gets heated up quickly than the air around the candle. That heated air moves upward and reaches the thermometer B which then shows a higher temperature.

10. 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.

Ans: Yes, Paheli can use a woollen cloth to wrap around a glass cold drink to keep it cool because wool is a bad conductor of heat and doesn't let the heat transfer from the inner atmosphere to the outer atmosphere.

11. In a mercury thermometer, the level of mercury rises when its bulb comes in contact with a hot object. What is the reason for this rise in the level of mercury?

Ans: When mercury is heated in a thermometer it gets expanded. After the expansion, the mercury atoms try to move outwards. Since they can not move down the thermometer and they find their required space upwards, hence they rise above in the thermometer.

### Short Answer Questions

12. A circular metal loop is heated at point O as shown in Figure 4.6.

(i) In which direction would heat flow in the loop?

Ans: When the metal loop is heated at O, then the heat will flow in the direction from O to P and O to R at a nearly equal rate.

(ii) In which order the pins at points P, Q and R fixed with the help of wax fall if points O, P, Q and R are equidistant from each other?

Ans: The pins located at the points R and P will fall almost at the same time and after that the pin at point Q will fall in the end.

13. In the arrangements A and B shown in Figure 4.7, 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.

Ans: In the first case A, the metal loop is circular hence the heat flows in two directions at an equal rate and reaches the point P and Q at the same time so they are likely to fall at the same time. Whereas in case B, the metal rod is straight and the heat flows in only one direction hence the heat reaches the point P first and then at point Q. In that case, P gets heated up earlier and falls before Q.

14. 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.

Ans: Due to the lower temperature, the setting of curd can be difficult. Some ways to set curd in such a situation is to keep the container warm either by wrapping it with a woollen cloth or by keeping it in a heat resistant container. In some places, the container is kept on the ashes of firewood to maintain the required temperature.

15. You may have noticed that a few sharp jerks are given to the clinical thermometer before using it. Why is it done so?

Ans: Before using a thermometer, few jerks are given in order to measure an accurate reading of the temperature. The jerks allow the mercury level to flow into the bulb below the normal temperature.

16. Why is it advised not to hold the thermometer by its bulb while reading it?

Ans: A thermometer is not advised to hold by its bulb while reading temperatures because it may affect the actual reading measured by the thermometer. A thermometer is always advised to hold from its top end.

17. At a campsite there are tents of two shades – one made with black fabric and the other with white fabric. Which one would you prefer for resting on a hot summer afternoon? Give reason for your choice. Would you like to prefer the same tent during winter?

Ans: Black coloured objects are good at the absorption of heat and they do not reflect much light. Whereas, white coloured objects are not good at absorbing heat and they reflect light. Hence, a white fabric tent should be considered on a hot summer to keep the atmosphere cooler. Whereas, a black fabric tent should be considered for winters to keep the inner atmosphere warmer than the outside.

18. While constructing a house in a coastal area, in which direction should the windows preferably face and why?

Ans: In coastal areas, very soothing and cool air flows from the sea to the direction of the coast. They are known as sea breezes. Hence, in order to keep a house fully ventilated, the windows of the house must face in the direction of the sea to keep the house cool and fresh.

19. Observe the picture given as Figure 4.8. Water is being boiled in a pan of wide base.

(i) Which position P or Q will feel warmer?

Ans: Position Q will feel warmer because when the water gets boiled the air above the pan will be heated more and earlier than the air around the pan. The hot air above the pan will move in the upward direction making the above atmosphere hotter.

(ii) Fill up the boxes P and Q to indicate the mode of flow of heat to the hand.

Ans: The mode of heat flow at point Q is due to contact between fluids which are known as convection while the flow of heat at point P is without the actual contact of molecules which is known as radiation.

20. Look at Figure 4.9.

The length of wire PQ in case of A is equal to the diameter of the semicircle formed by the wire CDE, in case B. One pin is attached to each wire with the help of wax as shown in Figure 4.9. Which pin will fall first? Explain.

Ans: The pin which is attached to the wire PQ in case A will fall first because the flow of heat is along a straight path which is faster than the flow of heat along a semi-circular path CDE in case B. Hence, the heat will reach to the end of wire PQ before reaching the end of wire CDE.

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### Types of questions in Class 7 Science NCERT Exemplar Solutions Chapter 4 Heat

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• The first seven questions in the Class 7 Science NCERT Exemplar Solutions Chapter 4 Heat are Multiple Choice Type questions. We have provided the answers to these questions along with their explanations as to why a specific option is right.

• Then there are very short answer type questions, which you have to answer in two or three lines.

• After that, there are short answer-type questions in which you have to provide answers with some explanations.

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