Thermal Energy Transfer

A mass m of ice at a temperature of –5 °C is changed into water at a temperature of 50 °C.

Specific heat capacity of ice = c_i

Specific heat capacity of water = c_w

Specific latent heat of fusion of ice = L

Which expression gives the energy needed for this change to occur?

• 55 m c_w + m L

• 55 m c_i + 5 m L

• 5 m c_i + 50 m c_w + m L

• 5 m c_i + 50 m c_w + 5 m L

A fixed mass of water is heated by an electric heater of unknown power P. The following quantities are measured

I. mass of water

II. increase in water temperature

III. time for which water is heated.

In order to calculate P, the specific heat capacity of the water is required. Which are also required?

• I and II only

• I and III only

• II and III only

• I, II and III

A liquid is initially at its freezing point. Energy is removed at a uniform rate from the liquid until it freezes completely.

Which graph shows how the temperature T of the liquid varies with the energy Q removed from the liquid?

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Two objects are in thermal contact with each other. Which of the following will determine the direction of the transfer of thermal energy between the bodies?

• The mass of each body

• The area of contact between the bodies

• The specific heat capacity of each body

• The temperature of each body

Water at a temperature of 0 °C is kept in a thermally insulated container. A lump of ice, also at 0 °C, is placed in the water and completely submerged.

Which of the following is true in respect of both the net amount of ice that will melt and the change in temperature of the water?

• A

• B

• C

• D

Thermal energy is added at a constant rate to a substance which is solid at time t = 0. The graph shows the variation with t of the temperature T.

                                  

         Which of the statements are correct?

I.       The specific latent heat of fusion is greater than the specific latent heat of vaporization.

II.      The specific heat capacity of the solid is less than the specific heat capacity of the liquid.

• I only

• I and II

• II only

• Neither I nor II

A system consists of an ice cube placed in a cup of water. The system is thermally insulated from its surroundings. The water is originally at 20 °C. Which graph best shows the variation of total internal energy U of the system with time t?

• A

• B

• C

• D

Two stars A and B emits the same amount of light. The wavelength that star A emits is longer than the wavelength that star B emits. What can you conclude from that explanation?

• A. The frequency of star A is higher than star B

• B. The frequency of star B is higher than star A

• C. The temperature of star A and star B is same

• D. The temperature of star A is higher than star B

• E. The temperature of star A is lower than star B

Which object has the highest temperature?

• A

• B

• C

• D

• F

According to Stefan's Law, if a star were to double its temperature (from 2000K to 4000K), the energy being emitted from that star would increase by a factor of...?

• 2

• 4

• 8

• 16