Practice questions · Convection

Up, over, down, around.

Six original Cambridge-style questions on what convection is, why warm fluid rises, why solids cannot convect, and where convection currents show up in daily life.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Always go through density

Warm fluid expands, becomes less dense, rises.

Heated fluid expands and so becomes less dense.
Less dense fluid rises; cooler, denser fluid sinks to replace it.
The loop this forms is the convection current. It needs a fluid, so not in solids.

[2 marks]

Define convection, and state which states of matter it can occur in.

Convection is the transfer of thermal energy by the movement of the fluid itself. ✓
It occurs in liquids and gases (fluids). ✓

Analysis

[3 marks]

Explain why a region of fluid that has been heated rises.

The heated fluid expands, so the same mass takes up more volume. ✓
This makes it less dense than the surrounding cooler fluid. ✓
Being less dense, it rises (floats up) through the denser fluid. ✓

Analysis

[2 marks]

Explain why convection cannot take place in a solid.

In a solid the particles are held in fixed positions and cannot move from place to place. ✓
So the material cannot flow to carry energy, which is what convection requires. ✓

[2 marks]

State two everyday situations in which energy is transferred by convection.

Water being heated in a pan or kettle (warm water circulates). ✓
A room being warmed by a radiator (warm air rises and circulates). ✓

Sea and land breezes are another good example.

Analysis

[3 marks]

A heater for a room is usually placed near the floor rather than near the ceiling. Explain why this helps to warm the whole room.

Air warmed near the floor expands, becomes less dense and rises. ✓
Cooler air sinks to take its place and is warmed in turn, setting up a convection current. ✓
This current circulates warm air around the whole room. ✓

A heater near the ceiling would leave the warm air trapped at the top.

Analysis

[2 marks]

A student says "hot air rises because heat goes up." Give a more precise physics explanation of why the warm air rises.

The warm air rises because it has expanded and become less dense than the cooler air around it. ✓
The denser, cooler air sinks and pushes the less dense warm air upward. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.