World GK Questions and answers pdf - 3

Question: 11

What are insulators?

Materials which do not allow heat to pass through them are called poor conductors of heat or insulators.

Question: 12

Give the differences between boiling and evaporation?

Boiling

1. Boiling is a visible, rapid process.

2. Boiling takes place at a fixed temperature called boiling point.

3. Boiling does not produce cooling.

4. Boiling takes place throughout the liquid.

5. During boiling, there is no change in temperature.

Evaporation

1. Evaporation is a slow invisible process.

2. Evaporation takes place at all temperatures.

3. Evaporation produces cooling effect.

4. Evaporation takes place on the surface of liquid.

5. During evaporation, there is a variation in temperature.

Question: 13

State the principles of a refrigerator?

When a liquid evaporates it takes in heat energy and cools its surroundings. When the gas condenses back to a liquid , the latent heat is released. This cause cooling.

Question: 14

What is thermal expansions?

The expansion of an object due to heat is called thermal expansion.

Question: 15

What is the use of bimetallic strip?

A bimetallic strip can be used in a thermostat to break an electric circuit.