Transfer of Thermal Energy

Explain how the temperature of the rest of the air in the freezer decreases.

The plastic material in the insulation is a poor thermal conductor.

Describe how thermal energy is transferred through a plastic material.

The plastic material also contains a large number of small air bubbles.

Explain how the air bubbles reduce the transfer of thermal energy through the insulation.

The results are shown in Fig. 2.2.

Draw a line linking each type of surface with the appropriate meter reading. One line has been drawn for you.

The hot surfaces produce a convection current in the air outside the metal cube.

Describe how the convection current is produced.

Explain the process that causes the water above X to increase in temperature.

Heater Y remains switched off. Explain why the temperature of the water below heater X increases much more slowly than the temperature of the water above heater X.

The hot water tank is covered in a thick layer of insulating material. The material is a plastic that contains a large number of small pockets of trapped air.

Explain why this material is a good insulator.

Describe how heat is transferred through the metal and then to all of the liquid in the cup.

A cup of a different shape is placed on the same heater, as shown in Fig. 3.2. The two cups are made of the same metal and contain the same amount of coffee.

Explain why the coffee in the cup in Fig. 3.2 is not kept as warm as the coffee in the cup in Fig. 3.1.

The outside surface of the cup can be either black or white and can be either dull or shiny.

(i) Underline which colour and which type of surface is best to keep the coffee warm.

black $\qquad$ white $\qquad$ dull $\qquad$ shiny

(ii) Explain your answer to (c)(i).

Explain why wood is a suitable material for the handle of the saucepan.

Describe and explain, in terms of free electrons, how thermal energy is transferred through the copper base of the saucepan.

Describe and explain how thermal energy is transferred upwards through the water.

Explain what is meant, in this case, by radiation.

conduction,

______

convection.

______

No thermal energy (heat) is transferred from the surface of the Sun to the Earth by either conduction or convection.

Explain why this is so.

In a certain country, the climate is very sunny and hot during the day and extremely cold during the night.

Explain how painting the houses white helps to maintain a comfortable temperature both during the day and during the night.

during the day: ______

during the night: ______

Describe how thermal energy in the red-hot metal screen is transferred to the man and how it warms him.

At the top of the heater is a metal hood that has a shiny lower surface.

Explain why this makes the energy transfer from the metal screen more efficient.

The air temperature decreases and the man puts on a black pullover.

Explain one way in which wearing the black pullover helps to keep the man warm.

Describe, using ideas about particles, how the conduction of heat takes place in glass and in iron. You should make it clear why iron is a better conductor of heat.

conduction in glass ______

conduction in iron ______

Describe how heat is transferred throughout the water in the glass flask.

At the beginning of the day, the heater releases thermal energy at a greater rate than later in the day.

Suggest why.

Fig. 10.2 is a diagram of the heater standing on the floor of the room and placed next to one of the walls.

Describe, and explain in detail, how the thermal energy is transferred throughout the room. You may draw on Fig. 10.2.

State one method of thermal insulation that is used to keep a room warm, and explain why it is effective.