# Physics - Conduction and Convection (AQA Syllabus A)

The transfer of heat energy is studied in GCSE Science. This is the fourth of eight quizzes on the topic and it looks specifically at the processes of conduction and convection.

Heat is thermal energy. It only ever travels in one direction - from warmer to cooler. You may have heard people say 'close the door to keep the cold out' but they really should be saying 'close the door to keep the warmth in'. Heat travels in 3 ways, but this quiz is concerned with only two of them - conduction and convection, which both involve the movement of particles.

Heat energy can move through any solid by conduction. Metals are usually good conductors of heat but liquids, gases and solids made mainly from non-metals are usually poor heat conductors. Poor conductors of heat are called 'insulators'.

Thermal energy is transferred from the hot end of a solid to the cold end. In metals, this process is very efficient because the particles are very closely packed and there are free electrons in the structure. In materials made mainly from non-metallic elements there are no free electrons and the atoms are fixed in place differently, so the heat doesn't get passed on as easily.

Heat is transferred through liquids and gases (fluids) by convection. The particles of fluids are free to change places. When heated, there is more kinetic energy in the particles so they move around more than they did before they were heated. Because they are moving faster, they are further apart which means there are fewer particles in each cm3 - the fluid is therefore less dense. As you know, less dense things float to the top in fluids. The heated part of the fluid rises to the top and cooler fluid moves in to take its place. This is called a convection current and, as it circulates, heat is spread through the entire fluid.

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1. In what substances can convection occur?
Convection occurs in any fluid
2. What is the main way that heat passes through a brick in the wall of a building?
A brick is an opaque solid so the only way heat can pass through it is by conduction
3. Why are metals good heat conductors?
As well as having close packed particles, the free electrons in their structure can transport the heat energy through the metal
4. Thunderstorms are created by which form(s) of energy transfer in the atmosphere?
Thunderstorms are created when large amounts of hot moist air rise through the atmosphere. As the moist air rises it cools and the moisture condenses to form rain. The size and speed of movement in this enormous convection current creates high winds and static electricity sparks which you see as lightning
5. "Particles with more energy move in to take the place of particles with less energy"
What method of heat transfer is being described in the previous sentence?
Whenever you see a question that deals with heat transfer by moving particles it has to be convection
6. Which state(s) of matter is (or are) fluids?
Fluids are substances that can flow
7. Houses built with thick stone walls usually stay cooler inside during the summer than houses built with thinner brick walls. Why might this be?
This question is testing if you know that one of the factors affecting conduction is the thickness
8. On a sunny day, why is it slightly harder to swim back to the shore of a lake than to swim towards the centre?
Since water is transparent the sun can't heat it directly. At the edge, it heats the bed of the lake since the water is shallow. The warmth of the lake bed transfers heat to the water, making it less dense. The less dense water rises, creating a convection current that flows away from the shore. A strong swimmer would probably not notice the difference
9. How does extra heat affect the particles of a metal?
The particles of any solid are fixed in place so the increased energy available from the heat makes them vibrate more vigorously
10. Why do hot air ballons rise?
Less dense air will rise, exactly as in a convection current. Because it is trapped in the balloon, the balloon goes with it