Heat, Class 7th Notes

THESE NOTES ARE PREPARED ACCORDING TO JKBOSE SYLLABI IN SIMPLIFIED AND CONCISE PATTERN

Exercises

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

Ans:
Similarities:

Both thermometers contain mercury.
Both thermometers have Celsius scale.
Both thermometers are made of glass.

Differences:

The range of Clinical thermometer is 35 C to 42 C whereas the range of Labodatory thermometer is -10 C to 110 C.

Clinical thermometer measures body temperature whereas laboratory thermometer is used to measure temperature in labs.

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

Ans:
Conductors: Iron, Copper, Aluminium etc
Insulators: Rubber, Plastic, Wood etc

3. Fill in the blanks

a. The hotness of 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 is dipped in a cup of hotmilk. 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:

Ans:

i. Land breeze blows during:: d. Night

ii. Sea breeze blows during :: c. Day

iii. Dark clothes are preferred during:: b. Winter

iv. Light 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: It is because the air is trapped in between the layers of clothes.

Air is a bad conductor of heat and prevents flow of heat from our body.

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

Ans:

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

The heat is transferred from burner to the utensil by Conduction

Inside the utensil, the heat is transferred between water molecules by convection.

The heat is tansferred from the utensil to the sorroundings by radiation.

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

Ans: It is because the white light reflects most of the heat falling on it and thus keeps the house cooler.

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

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

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

Ans: (d) between 30C and 50C

9. An iron ball at 40C is dropped in a mug containing water at 40C. 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: (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:

(a) becomes cold by the process of conduction.

(b) becomes cold by the process ofconvection.

(c) becomes cold by the process of radiation.
(d) does not become cold.

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

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