Energy transfers and efficiency

• The rate at which a material transfers thermal energy depends on a number of factors. The efficiency of a device is a measure of how much useful energy it transfers.
• The rate at which thermal energy is transferred through a wall of a house depends on:

  1. The difference in temperature between the warmer interior and colder exterior
  2. The thickness of the walls
  3. The thermal conductivity of the walls
• All machines waste some of the energy they transfer - most machines waste energy as heat energy
• The efficiency of a machine is a way of saying how good it is at transferring energy into useful forms.
• A very efficient machine has an efficiency that is nearly 100 % - the higher the efficiency the better the machine is at transferring energy into useful forms.
• You can reduce unwanted energy transfers for example through lubrication to reduce friction or using wires with low resistance in electrical circuits. This can also increase the efficiency of an intended energy transfer.
• A material with a high thermal conductivity is a better conductor of energy than one with a lower thermal conductivity.