Class 7 - Chemistry - Heat

Question 1:

List out the similarities and dissimilarities between the laboratory thermometer and the clinical thermometer?

Answer:

Similarities between the laboratory thermometer and the clinical thermometer are as follows:-

  1. Laboratory thermometer and the clinical thermometer thermometers consist of long narrow uniform glass tubes.
  2. Laboratory thermometer and the clinical thermometer have a bulb at one end.
  3. Laboratory thermometer and the clinical thermometer contain mercury in the bulb.
  4. Laboratory thermometer and the clinical thermometer use Celsius scale on the glass tube.

 

Differences between the laboratory thermometer and the clinical thermometer:

  1. A clinical thermometer reads temperature 35°C to 45°C while the range of laboratory thermometer is -10°C to 110°C.
  2. The clinical thermometer has a kink near the bulb while there is no kink in the laboratory thermometer.
  3. Due to kink, mercury does not fall down on its own in clinical thermometer.

 

 

Question 2:

Give two examples each of conductors and insulators of heat.

Answer:

Conductors: Copper, aluminium and iron.

Insulators: Wood, water and air.

 

 

Question 3:

Fill in the blanks:

(a) The hotness of an object is determined by its __________.

(b) Temperature of boiling water cannot be measured by a _____________ thermometer.

(c) Temperature is measured in degree ______________.

(d) No medium is required for transfer of heat by the process of __________.

(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of ______________.

(f) Clothes of ______________ colours absorb heat better than clothes of light colours.

Answer:

(a) The hotness of an object is determined by its temperature.

(b) Temperature of boiling water cannot be measured by a clinical thermometer.

(c) Temperature is measured in degree Celsius.

(d) No medium is required for transfer of heat by the process of radiation.

(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of conduction.

(f) Clothes of dark colours absorb heat better than clothes of light colours.

 

 

Question 4:

Match the following:

(i) Land breeze blows during                                         (a) summer

(ii) Sea breeze blows during                                           (b) winter

(iii) Dark coloured clothes are preferred during          (c) day

(iv) Light coloured clothes are preferred during         (d) night

Answer:

(i) Land breeze blows during                                            (d) night

(ii) Sea breeze blows during                                               (c) day

(iii) Dark coloured clothes are preferred during             (b) winter

(iv) Light coloured clothes are preferred during            (a) summer

 

 

Question 5:

Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.

Answer:

More layers of clothing actually keep us warmer in winters as they have a lot of space between them.

That space gets filled up with air. Air acts as insulator of heat. Air acts as insulator of heat.

This layer prevents our body heat to escape in the surroundings.

 

 

Question 6:

Look at Fig. 4.13. Mark where the heat is being transferred by conduction, by convection and by radiation.

 Class_7_Chemistry_Heat_Heat_Transferred

 

 

Answer:

 

 Class_7_Chemistry_Heat_Heat_Transferred1

 

 

Question 7:

In places of hot climate it is advised that the outer walls of houses be painted white.

Explain?

Answer:

In places of hot climate it is advised that the outer walls of houses be painted white because white colour reflects most of the

heat that falls on it or we can say it absorbs less amount of heat. Therefore, the temperature inside the house does not increase very much.

Question 8:

One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be

(a) 80°C                                (b) more than 50°C but less than 80°C

(c) 20°C                               (d) between 30°C and 50°C

Answer:

Correct Option: (d) between 300 and 500

This happens because heat gained by cold water will be equal to the heat lost by the hot water.

Question 9:

An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will

(a) flow from iron ball to water.

(b) not flow from iron ball to water or from water to iron ball.

(c) flow from water to iron ball.

(d) increase the temperature of both.

Answer:

Correct Option: (b) not flow from iron ball to water or from water to iron ball.

 

 

Question 10:

A wooden spoon is dipped in a cup of ice cream. Its other end

(a) becomes cold by the process of conduction.

(b) becomes cold by the process of convection.

(c) becomes cold by the process of radiation.

(d) does not become cold.

Answer:

Correct Option: (d) does not become cold.

 

 

 

Question 11.

Stainless steel pans are usually provided with copper bottoms. The reason for this could be that

(a) copper bottom makes the pan more durable.

(b) such pans appear colourful.

(c) copper is a better conductor of heat than the stainless steel.

(d) copper is easier to clean than the stainless steel.

Answer:

Correct Option: - (c) Copper is a much better conductor of heat than that of stainless steel.

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