Explain how efficiency can be increased

The idea

Efficiency compares the useful energy transferred by a device with the total energy supplied to it, so it rises when less energy is wasted, usually as heat to the surroundings. To increase efficiency you reduce unwanted transfers: lubricate moving parts so friction transfers less energy to thermal stores, streamline shapes to cut drag, insulate or seal a system so less heat escapes, and use components that convert a larger fraction of the input into the intended output. For example, oiling a bicycle chain means more of the cyclist's energy reaches the wheels rather than warming the chain and air. Efficiency is a ratio, so it has no unit and cannot exceed 1 (or 100%).

What earns the marks

• Identifies that efficiency increases when the proportion of energy usefully transferred rises relative to the total energy supplied.
• Names a method that reduces wasted energy, such as lubrication to reduce friction or streamlining to reduce drag.
• Explains that reducing unwanted transfers to the surroundings, often as heat, raises the useful fraction of the input.
• States that efficiency is a ratio with no unit and cannot be greater than 1 or 100%.

Common mistakes and how to put them right

• Claims that efficiency can be increased by supplying more energy.

  Put it right: Recognise that extra input does not change the ratio unless the wasted fraction falls.

• Assumes efficiency can reach or exceed 100%.

  Put it right: Wasted energy always exists, so the value stays below 1.

• Treats lubrication as adding energy to the system.

  Put it right: Explain that it reduces energy dissipated by friction instead.

Exam tips

• Read every option and reject any that claims efficiency can exceed 100%.
• Link each method to the specific wasted transfer it reduces, such as friction or air resistance.
• Remember efficiency is a ratio, so choose the option that describes a proportion rather than a quantity of energy.