Efficiency can be defined as an energy conversion process. This conversion process is useful energy or work output divided by total energy input or energy stored multiplied by one hundred percent.

During higher (increased) efficiency levels, this is interpreted as energy that can do the same job, but requires a smaller amount of energy.

Each electrical device has a different level of efficiency. The laws of thermodynamics places a limit on the efficiencies that can be attained while trying to obtain some energy conversions.

Efficiencies are obtainable by either:

1. Mechanical energy to electrical.
2. Electrical to mechanical.
3. Chemical to thermal.
4. Chemical to thermal to mechanical to electrical.
5. Nuclear to thermal to mechanical to electrical.
6. Chemical to thermal to mechanical.
7. Electrical to light.
8. Light to electrical.

One has to be careful when comparing efficiencies. The entropy of the system determines the ease of obtaining high efficiencies. The devices with the smaller efficiencies include solar photovoltaic cells, which turn light into electricity - a relatively complex process. Meanwhile, a device with the larger efficiencies include a toaster, which converts electricity to heat. Electrical energy is easy to turn into heat -- while vice versa is much more difficult.

If a multi-step process is necessary the overall efficiency is equal to the product of each individual efficiency.


"Efficiency" and efficiency charts are found inside our textbooks on pages 79-81.