Physics Chapter 11 - Thermal Energy Transfer

A liquid is heated in a beaker.

The density of the liquid changes as its temperature increases. This causes energy to be transferred throughout the liquid.

How does the density change and what is this energy transfer process?

• The density decreases and the energy transfer process is conduction

• The density decreases and the energy transfer process is convection

• The density increases and the energy transfer process is conduction

• The density increases and the energy transfer process is convection

A rod is made half of glass and half of copper. Four pins A, B, C, and D are attached to the rod by wax. The rod is heated in the centre as shown.

The pins fall off when the wax melts.

Which pin falls off first?

• A

• B

• C

• D

Which process involves convection?

• Bread toasting under a grill

• Energy from the Sun warming a road surface

• Hot air rising to the top of a cool room

• Thermal energy transfer through a copper bar

A student suggests some uses for containers made from good thermal conductors and for containers made from poor thermal conductors.

In which row are both suggested uses correct?

• A

• B

• C

• D

A cotton sheet is ironed with a hot electric iron.

How is energy transferred through the metal base of the iron to the sheet?

• By conduction only

• By convection only

• By radiation only

• By convection and radiation only

Two plastic cups are placed one inside the other. A small spacer keeps the two cups separated. Hot water is poured into the inner cup and a lid is put on top, as shown in figure.

Which statement is correct?

• The bench is heated by convection from the bottom of the outer cup

• The lid reduces the energy lost by convection

• There is no thermal conduction through the sides of either cup

• Thermal radiation is prevented by the small air gap

A solid is heated from room temperature.

The graph shows how its temperature changes with time as it is heated constantly.

At which time has it just become completely liquid?

• A

• B

• C

• D

Thermal energy travels through space from the Sun to the Earth. Space is a vacuum.

How is thermal energy transferred from the Sun to the Earth?

• By conduction only

• By convection only

• By radiation only

• By convection and radiation

The diagram shows a vacuum flask used to keep liquid hot.

How does thermal energy pass through the vacuum?

• Conduction only

• Convection only

• Radiation

• Conduction and convection

One method of heat transfer involves the energy travelling at a much greater speed than in other methods.

What is the name of this method?

• Conduction

• Convection

• Evaporation

• Radiation