Simple Consequences of Energy Transfer
Conduction
- The main means of thermal energy transfer in solids
- When heated, atoms vibrate more, knocking into each other and transferring energy from atom to atom as a result
- Metals are excellent conductors; Non-metals are poor; Liquids and gases are very poor
- If a question mentions metals, the answer will probably have something to do with conduction
- Trapped air is a very good insulator of heat. Air is a gas and so is a poor conductor. Trapping it prevents it from circulating and forming a convection current
Thermal energy is transferred from the hot coffee to the mug and to the cold hands
- The mechanism by which the thermal energy is transferred is by either conduction, convection or radiation
- In this case the diagram focuses on conduction
Convection
- The means of thermal energy transfer in liquids and gases
- When heated, a gas will expand and become less dense. This causes it to rise (a convection current). Cooler (denser) gas falls, replacing the hot gas
- If a question refers to a liquid or gas (that isn’t trapped) then convection currents will probably form
- Heat sources placed at the bottom of things will generally create convection currents. Likewise, cooling units placed high up will cool any rising air, causing it to sink again
Thermal energy is transferred from the hot coffee to the air by convection currents rising from the surface
- The mechanism by which the thermal energy is transferred is by either conduction, convection or radiation
- In this case the diagram focuses on convection