Solution of Chapter 4. Heat (NCERT - Exemplar Science Book)

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

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

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 statement is true?

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?

Four arrangements to measure the temperature of ice in a beaker with a 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?

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

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

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

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 a reason for your answer.

To keep her soup warm Paheli wrapped the container in which it was kept with a woolen cloth. Can she apply the same method to keep a glass of cold drink cool? Give a reason for your answer.

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?

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

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

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.

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, the setting of curd becomes difficult. Suggest a way to set curd in such a situation.

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

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

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

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

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

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

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

Look at Figure 4.9. Fig. 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.