NCERT Class 7 Science Fourth Chapter Heat Exercise Solutions

Heat

Inside Questions:

(1) What is called temperature?

Ans. A reliable  measure of the hotness of an   object is its temperature.

(2) What is  called thermometer?

Ans.  Temperature is  measured by a device called  thermometer.

(3) What is called clinical thermometer?

Ans . The thermometer that measures our body temperature is called a clinical thermometer.

(4) Write 3 precautions to be observed while using a clinical  thermometer?

Ans. The three precautions to be observed while using a clinical thermometer are as follows-

(1) Thermometer should be washed before and after use, preferably with an

antiseptic solution.

(2) Ensure that before use the mercury level is below 35°C.

(3) Read the thermometer keeping the level of mercury along the line of sight.

(5) What is the normal temperature of human  body?

Ans: 37 degree Celsius.

(6) What is called the maximum and minimum  temperatures?

Ans . The maximum and minimum temperatures of the previous  day, reported in weather reports, are measured by a thermometer called the maximum -minimum thermometer.

What is  conduction?

Ans.  The process by which heat is transferred from the hotter end to the colder end of an object is known as conduction.

(7) What is the normal temperature of human  body?

Ans: 37  degree  celsius.

(8) What is called the maximum and minimum temperatures?

Ans: The maximum and minimum temperatures of the previous  day, reported in weather reports, are measured by a thermometer called the maximum -minimum thermometer.

(9) What is conduction?

Ans:  The process by which heat is transferred from the hotter end to the colder end of an object is known as conduction.

Example: Aluminum, Iron and copper.

(10) What is poor conductors of heat?

Ans:  The materials which do not allow heat to pass through them easily are poor conductors of heat.

Example: Plastic  and wood.

(11) What is  called sea  breeze?

Ans:  The air from the sea is called the sea breeze.

(12) What is called  land breeze?

Ans: The cool air  from the land moves towards the sea.  This is called the land breeze.

(13) Define radiation?

Ans:  From the sun the heat comes to us by  another process known as radiation.

(14) What is called convection?

Ans: When water is heated, the water near the flame gets hot. Hot water rises up. The cold water from the sides moves down towards the source of heat. This  water also gets hot and rises and water from the sides moves down.  This process continues till the whole water gets heated. This mode of heat  transfer is known as convection.

EXERCISE Questions:

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

Ans. Similarities:
(i) Both thermometers consist of long narrow uniform glass tubes.
(ii) Both have a bulb at one end.
(iii) Both contain mercury in bulb.
(iv) Both use Celsius scale on the glass tube.

Differences:
(i) A clinical thermometer reads temperature 35°C to 45°C while the range of laboratory thermometer is -10°C to 110°C.
(ii) Clinical thermometer has a kink near the bulb while there is no kink in the laboratory thermometer.
Due to kink mercury does not fall down on its own in clinical thermometer.

(2) Give two examples each of conductors and insulators of heat.

Ans. Conductors—aluminum, iron Insulators—plastic, wood.

(3) Fill in the blanks:

(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. Heat is transferred to its other end by the process of conduction.

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

(4) Match the following:

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

Ans: More layers of clothing keep us warm in winters as they have a lot of space between them. This space gets filled up with air. Air is a bad conductor, it does not allow the body heat to escape out.

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

(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 wall of houses be painted white because white colour reflects heat and the houses do not heat up too much

(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

Ans: Between 30^o and 50^o C.

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

Ans: (b) Not flow from iron ball to water or from water to iron ball.

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

Ans: (d) does not become cold.

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

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