Thermal Energy

Specific heat capacityThe specific heat capacity of a substance is

the amount of heat energy required to raise the temperature of the substance unit mass by a unit change in temperature.

The unit mass is usually 1kg, while the unit change in temperature is 1K or 1°C. The key formula is:

Energy = specific heat capacity × mass × change in temperature

Specific heat capacityCalculate the following:

How much energy is needed to increase the temperature of 500 g of lead from 20 ºC to 45 ºC? The specific heat capacity of lead is 128 J/kg/ºC.

Heat transferHeat is transferred naturally from

a substance with a higher temperature to a substance with a lower temperature.

Heat TransferComplete the following definition using the

words below:

___________ energy or heat is always transferred from a _________ place to a ___________ place. The amount of energy _____________ depends on how big the _______________ difference is

cooler thermal transferred hotter temperature

Heat transferDraw arrows to show the direction of energy transfer:

Heat transferHeat can be transferred in three ways.

1. Conduction - by a substance which does not move (solids).

2. Convection - by  substance which moves (liquids and gasses).

3. Radiation - infra-red radiation is exchanged between all substances.

Thermal conductionHeat can be transferred by conduction only

in solids.

If one end of a solid is heated, the particles of the solid gain kinetic energy.This means that the particles….

Thermal conductors Substances which are GOOD at transferring heat are known as THERMAL CONDUCTORS, and substances which are BAD are know as THERMAL INSULATORS.

Thermal conductionIn solids the particles (what particles?) are

held together by strong forces of attractionThe only way particles can move is to vibrate

forwards and backwardsWhen the solid is heated, the amount by which

the particles vibrate is increased. (This is what is meant by saying that the particles of the solidhave gained kinetic energy.

The increase in energy (heat) is passed onto the next particle, which in turn starts to vibrate more.

Thermal conductionThe following image shows what

happens when heat is applied to a metal bar

The length of the arrow indicates the amount of vibration in the particles