NCERT Class VII Science Solutions: Chapter 4 – Heat Part 3 (For CBSE, ICSE, IAS, NET, NRA 2022)

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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

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
  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.