Energy and Efficiency

Energy is measured in joules (J). This unit is used for all forms of energy.

The energy supplied to a machine is often called the input energy. From the conservation of energy we know that:

input energy (energy supplied) = useful energy transferred + energy wasted

The less energy that is wasted by a machine, the more efficient the machine

We can calculate the efficiency of any appliance that transfers energy, using the equation:

Efficiency = useful energy transferred by the appliance (x 100%)
total energy supplied to the appliance

No appliance can be 100% efficient, except an electric heater which usefully transfers all of the electrical energy supplied to it by heating the surroundings.

The energy transfer through an appliance can be represented with a Sankey Diagram

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Using Energy