Physics Revision (Theme 2: Thermal Physics)

A cup contains hot liquid. Some of the liquid evaporates.

What happens to the mass and what happens to the weight of the liquid in the cup?

• A

• B

• C

• D

Which statement about evaporation is correct?

• Evaporation causes the temperature of the remaining liquid to decrease.

• Evaporation does not occur from a cold liquid near its freezing point.

• Evaporation does not occur from a dense liquid, such as mercury.

• Evaporation occurs from all parts of a liquid.

A gas is stored in a sealed container of constant volume. The temperature of the gas increases.

This causes the pressure of the gas to increase.

What happens to the gas molecules during this pressure increase?

• The average kinetic energy of the molecules increases.

• The average separation of the molecules decreases.

• The average separation of the molecules increases.

• The volume of each molecule increases.

A liquid is evaporating. The liquid is not boiling.

Which statement about the liquid is correct?

• Any molecule can escape, and from any part of the liquid.

• Any molecule can escape, but only from the liquid surface.

• Only molecules with enough energy can escape, and only from the liquid surface.

• Only molecules with enough energy can escape, but from any part of the liquid.

The diagram shows a quantity of gas enclosed in a cylinder by a piston. The piston is moved to the left or to the right. The temperature of the gas is kept constant.

Which row describes the effect of moving the piston slowly in the direction shown in the table?

• A

• B

• C

• D

What causes the random, zig-zag movement (Brownian motion) of smoke particles suspended in

air?

• air molecules colliding with smoke particles

• convection currents as the hot smoke rises

• smoke particles colliding with each other

• smoke particles reacting with oxygen molecules in the air

The air in the bottle is heated by the Sun.

What is the effect on the average speed of the air molecules in the bottle, and the average distance between them?

• A

• B

• C

• D

Which row is correct for the evaporation of a liquid?

• A

• B

• C

• D

A swimmer feels cold after leaving warm water on a warm, windy day.

Why does she feel cold even though the air is warm?

• The less energetic water molecules on her skin escape quickly.

• The more energetic water molecules on her skin do not escape quickly.

• The water on her skin does not evaporate quickly enough to keep her warm.

• The water on her skin evaporates quickly and cools her skin.

Air is trapped in a cylinder by a piston. The pressure of the air is p and the length of the air column is 20 cm.

The piston is moved outwards until the length of the air column has increased by 40 cm. The temperature of the air remains constant.

What is the new air pressure?

• P/2

• P/3

• 2P

• 3P