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Heat (Physics) Class 7 - NCERT Questions
Q 1.

State similarities and differences between the laboratory thermometer and the clinical thermometer.

SOLUTION:

Similarity : Both contain mercury in bulb.
Difference : The laboratory thermometer is generally used to measure temperatures ranging from 0°C to 100°C.
The clinical thermometer has its range of measureable temperature from 35°C to 42°C.

Q 2.

Give two examples each of conductors and insulators of heat.

SOLUTION:

Conductors – Aluminium, iron
Insulators – Air, water

Q 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 process of _______________.
(E) A cold 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.

SOLUTION:

(A) Temperature
(B) Clinical
(C) of hotness
(D) Radiation (E) Conduction (F) Dark

Q 4.

Match the following :

SOLUTION:

(i) → s, (ii) → r, (iii) → q, (iv) → p

Q 5.

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

SOLUTION:

In winter, it is preferred to wear more layers of clothing because the air trapped in between the various layers prevents the flow of heat from our body to the cold surrounding and hence it keeps us warmer than wearing just one thick piece of clothing.

Q 6.

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

SOLUTION:

Q 7.

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

SOLUTION:

In places of hot climate, it is advised that outer wall of houses be painted white because white colour reflects heat and the houses do not heat up too much.

Q 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

SOLUTION:

As we know, heat flows from water at a higher temperature to water at a lower temperature, so temperature of the mixture will be between 30°C and 50°C.

Q 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.

SOLUTION:

As temperature of iron ball and water is same.

Q 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.

SOLUTION:

A wooden spoon is an insulator.

Q 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.

SOLUTION:

(iv)