IGCSE Thermal Physics

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 a 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.

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 gas in a container is heated but is kept at constant volume.

Why does the gas pressure increase?

• The molecules expand

• The molecules increase in mass

• The molecules move further apart

• The molecules move more rapidly

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

The diagram shows a beaker of water. Four molecules are levelled. The relative amount of energy of each molecule is shown.

Which molecule is most likely to escape from the liquid?

• Molecule A

• Molecule B

• Molecule C

• Molecule D

The volume of gas in a sealed syringe is increased. The temperature of the gas does not change.

After this change is made, what has happened to the gas molecules in the syringe?

• They move more quickly

• They move more slowly

• They hit the syringe walls less often

• They hit the syringe walls more often

The diagram shows four labelled changes of state between solid, liquid and gas.

Which changes need an energy input?

• P and Q

• Q and R

• R and S

• S and P

Which diagram best shows the path of a gas molecule?

• A

• B

• C

• D

The molecules of a substance become more closely packed and move more quickly.

What is happening to the substance?

• A gas is being heated and compressed.

• A gas is being heated and is expanding.

• A liquid is boiling.

• A liquid is evaporating at room temperature.