Energy transfer and waste

HideShow resource information

Energy cannot be created or destroyed when it is transferred. All energy is usefully transferred, dissipated of stored. The energy that spreads to the surroundings is called wasted energy.

A sankey diagram represents energy transfer in a device.

The energy input is shown at the left side of the arros. The arrow splits. Each section shows the output energy form. The width of each part of the arrow shows the proportion of energy it represents.

Comparing devices

Sankey diagrams compare the proportion of energy transferred usefully by different devices.


Efficient devices do not waste much energy. Efficiency = useful energy out / total energy in.

The answer is always a decimal less than 1. Then convert to a percentage by multiplying the answer by 100. Efficiency is always less than 100%.

Perpetual motion machines cannot be made as they would eb 100% efficient, which is impossible.

Electrical appliances

Electrial appliances transfer the energy supplies by electricity into something useful.

Mains electricity is convenient, safe and pollution free at the point of use. However, generating electricity in power stations causes pollution.

Batteries change chemical energy into electricity when the battery is part of a circuit.

Alternatives to electricity include gas or biomass for cooking, lighting and transport.

Some appliances work using solar power or energy stored in springs instead of batteries.


LEDs produce light but work in a different way to light bulbs. Electrons in materials used to makes LEDs absorb energy from a supplied voltage. Then they release this energy as light. The light is a single colour because the same energy is absorbed and released by all electrons in an LED.

How much energy is used?

Power is the


No comments have yet been made

Similar Physics resources:

See all Physics resources »See all Energy resources »