NCERT Class VII Science Solutions: Chapter 4 – Heat Part 3

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VERY SHORT ANSWER QUESTIONS

Question 8:

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

Answer:

They must use some insulating material like, sack, saw dust, newspaper, etc. to cover the ice.

Question 9:

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

Result for flame of a candle

Flame of a Candle

Result for flame of a candle

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

Answer:

Thermometer B will show a greater rise in temperature because hot air rises up or air on the top of the candle flame is getting heated by convection.

Question 10:

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 reason for your answer.

Answer:

Yes, she can apply the same method to keep a glass of cold drink cool because wool is a thermal insulator, and it cannot allow heat to pass through it.

Question 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?

Answer:

Mercury expands when heated. Hence, it rises in the capillary tube.

SHORT ANSWER QUESTIONS

Question 12:

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

Result for metal loop is heated

Metal Loop is Heated

Result for metal loop is heated

  1. In which direction would heat flow in the loop?

  2. In which order the pins at points P, Q and R fixed with the help of wax fall if points O, P, Q and Rare equidistant from each other?

Answer:

  1. The heat will flow in both the directions i.e. from O to P and O to R.

  2. At first the pins at R and P will fall simultaneously followed by the pin at Q.

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