Two metal spheres have radii r and 2r and they emit thermal radiations with maximum intensities at wavelengths $\mathrm{\lambda }$ and 2$\mathrm{\lambda }$ respectively. The respective ratio of the radiant energies emitted by them per second will be:

1. 4 : 1

2. 1 : 4

3. 16 : 1

4. 8 : 1

A body cools down from 80°C to 60°C in 10 minutes when the temperature of the surroundings is 30°C. The temperature of the body after the next 10 minutes will be:

1. 30°C

2. 48°C

3. 50°C

4. 52°C

While finding specific heat capacity using a calorimeter, error might occur due to:

1. absence of insulating lid

2. absence of water equivalent

3. both 1 and 2

4. neither 1 nor 2

Gas thermometers are more sensitive than liquid thermometers because:

1. gases expand much more than liquids.

2. gases are easily obtained.

3. gases are much lighter.

4. gases do not easily change their states.

The amount of heat required to change the state of 1 kg of substance at constant temperatue is called:

1. Kilocal

2. Calorie

3. Specific heat

4. Latent heat

Refer to the plot of temperature versus time showing the changes in the state of ice on heating (not to scale).

Which of the following is correct?

1. The region AB represents water and steam in thermal equilibrium.

2. At B water starts boiling.

3. At C all the water gets converted into steam.

4. C to D represents water and steam in equilibrium at boiling point.

A black body, which is at a high-temperature T K, radiates thermal radiations at the rate of E W/m². If the temperature falls to T/4 K, the thermal radiations emitted in W/m² will be:

1. E

2. E/4

3. E/64

4. E/256

Two balls of the same material and same surface finish have their diameters in the ratio 1:2. They are heated to the same temperature and are left in a room to cool by radiation, then the initial rate of loss of heat:

1. Will be the same for the balls.

2. For larger ball is half that of another ball.

3. For larger ball is twice that of another ball.

4. For larger ball is four times that of the other ball.

The rate of radiation of energy from a hot object is maximum if its surface is:

1. White and smooth

2. Black and rough

3. Black and smooth

4. White and rough

"A good absorber is a good emitter" is explained by:

1. Stefan's law

2. Wien's law

3. Newton's law of cooling

4. Kirchhoff's law