Heat (NCERT Solutions, Class 7)

(1) State similarities and differences between the laboratory thermometer and the clinical thermometer.

Ans-

Differences between the clinical thermometer and laboratory thermometer

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Similarities between the clinical thermometer and laboratory thermometer

(i) Both thermometers are made of glass.

(ii) Both thermometers have mercury to measure the temperature.

(iii)Both thermometers can measure temperature in 0c.

(iv)Both thermometers have similar shapes.

(2) Give two example of conductors and insulators of heat.

Ans-

Example of conductors – Steel and Iron

Example of insulators-wood and plastic

(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…..

(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.

Ans-

(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.

(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

Ans-

(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

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

Ans-Air is trapped between the layers which prevents the flow of heat from our body to the cold surroundings. Hence we feel warm. So, wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.

(6) Look at the figure given below.  Mark the points where the heat is being transferred by conduction, by convection and by radiation.

Heat,Diagram of Q6, Ex, NCERT, Class 7, Science

Ans- Conduction, convection and radiation are marked in the given figure and shown below:

Heat, Ans 6, Ex, NCERT, Class 7, Science

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

Ans- In places of hot climate it is advised that the outer walls of houses be painted white because white colour transmits heat the most. So we feel less warm.

(8) One litre of water at 30o C is mixed with one litre of water at 50 o C. The temperature of the mixture will be

(a)80oC

(b)more than 50 oC but less than 80 oC

(c)20 oC

(d) between 30 oC and 50 oC

Ans-

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

(a)80oC

(b)more than 50 oC but less than 80 oC

(c)20 oC          

(d) between 30 oC and 50 oC

(9)An Iron ball at 40 oC is dropped in a mug containing water at 40 oC.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.

Ans-

An Iron ball at 40 oC is dropped in a mug containing water at 40 oC.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.

(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.

Ans-

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.

(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.

Ans-

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.

Helping Topics

Heat

Practice sheet, class7

 

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