• Heat (thermal energy)
• Light
• Sound
• Movement (kinetic energy)

For example, a hairdryer transfers electrical energy as heat and movement (kinetic). Some energy is wasted as sound.

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Efficiency

The more useful energy an appliance transfers, the more efficient it is.

Efficiency can be calculated using the following equation.

For example, if the hairdryer transferred 1 000 J of electrical energy into 350 J of heat, 150 J of movement energy and 500 J of sound, its efficiency would be calculated as follows.

The amount of energy that an appliance transfers depends on:

• How long the appliance is switched on for
• How fast the appliance transfers energy (its power)

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Measuring Energy and Calculating Cost

Energy is measured in joules (J), but this is a very small amount of energy. Instead electricity supply companies use a much bigger unit called the kilowatt-hour (kWh), or simply a unit.

The power of an appliance is measured in watts (W) or kilowatts (kW).

1 kW = 1 000 W

The number of kilowatts-hours of energy transferred to an appliance is calculated using this formula.

The cost of this energy can be calculated using this formula.

For example, if a washing machine has a power rating of 3 kW and is used for four hours per week what is the total cost if one unit of electrical energy costs 8 cents?

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