Thermal Transfers 1

A substance is heated at constant power. The graph shows how the temperature T of the substance with time t as the state of the substance changes from liquid to gas.

What can be determined from the graph?

•  The specific heat capacity of the gas is smaller than the specific heat capacity of the liquid

• The specific heat capacity of the gas is larger than the specific heat capacity of the liquid

• The specific latent heat of fusion of the substance is less than its specific latent heat of vaporization

• The specific latent heat of fusion of the substance is larger than its specific latent heat of vaporization

Energy is supplied at a constant rate to a fixed mass of a material. The material begins as a solid. The graph shows the variation of the temperature of the material with time.

The specific heat capacities of the solid, liquid, and gaseous forms of the material are Cs , Cl , and Cg respectively. What can be deduced about the values of Cs , Cl , and Cg?

• C_s > C_g > C_l

• C_l > C_s > C_g

• C_l > C_g > C_s

• C_g > C_s > C_l

A container with 0.6 kg of a liquid substance is placed on a heater at time t = 0s. The latent heat of vaporization of the substance is 200kJ/kg. The graph shows the variation of the temperature T of the substance with time t. 

What is the power of the heater?

• 1200 W

• 3000 W

• 4800 W

• 13300 W

Molecules leave a boiling liquid to form a vapor. The vapor and liquid have the same temperature. What is the change in the average potential energy and the average kinetic energy of these molecules when they move from the liquid to the vapor?

• A

• B

• C

• D

A sample of solid copper is heated beyond its melting point. The graph shows the variation of temperature with time. During which stage is there an increase in the internal energy of the copper?

• P, Q, and R

• Q only

• P and R only

• Q and R only

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

1. I . Mass of water

2. II. Increase in water temperature

3. III. Time for which water is heated

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

• I and II only

• I and III only

• II and III only

• I and II and III

A solid of mass m is initially at temperature ΔT below its melting point. The solid has specific heat capacity c and specific latent heat of fusion L. How much thermal energy must be transferred to the solid in order to melt it completely?

• mL

• mc + mLΔT

• mcΔT + LΔT

• mcΔT + mL

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

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

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