Efficiency

Definition of Efficiency

Efficiency is a measure of how well a device or system converts the total energy input into useful energy output. It is defined as the ratio of useful energy output to total energy input.

Efficiency = $\frac{\text{Useful energy output}}{\text{Total energy input}}$

Efficiency is always less than or equal to 1 (or 100% when expressed as a percentage) because no device can be perfectly efficient 013 some energy is always lost or wasted.

Efficiency can be expressed as a decimal (e.g. 0.75) or as a percentage (e.g. 75%).

Calculating Efficiency

To calculate efficiency, you must ensure that both the useful energy output and the total energy input are measured in the same units, usually joules (J).

The formula is:

Efficiency = $\frac{\text{Useful energy output (J)}}{\text{Total energy input (J)}}$

If you want efficiency as a percentage, multiply the decimal by 100.

For instance, if a machine uses 200 J of energy and produces 150 J of useful energy, the efficiency is:

$\text{Efficiency} = \frac{150}{200} = 0.75$ or 75%

Energy Wastage and Efficiency

In all energy transfers, some energy is wasted, usually as thermal energy (heat) that is not useful for the intended purpose.

Common causes of energy loss include:

• Friction between moving parts, which produces heat
• Electrical resistance in wires, which causes heat loss
• Sound energy produced by machines

Because of these losses, no machine or device can be 100% efficient.

Reducing wasted energy is important to save resources, reduce costs, and lower environmental impact.

Improving Efficiency

Efficiency can be improved by reducing the amount of energy wasted during energy transfers. Some common methods include:

• Insulation: Using materials that reduce heat loss, such as foam or fibre glass in buildings or jackets around pipes
• Lubrication: Applying oil or grease to moving parts to reduce friction and heat loss
• Energy-efficient devices: Using appliances designed to waste less energy, such as LED light bulbs or electric motors with low resistance