What is the exact definition of efficiency?

• A. Ability to perform work with a certain power and quality for a given time.
• B. The ratio of useful work performed to energy consumed.
• C. The rate at which energy is converted to heat.
• D. The amount of time required to complete a task.

Answer: (A)

Efficiency is the ratio of useful work performed to energy consumed. In practice, it means comparing what you actually get out of a process with what you put in, so you can see how much energy is lost to things like friction, heat, or other inefficiencies. Expressed as a percentage, it tells you how effectively energy is being used.

The idea of performing work with a certain power and quality for a given time describes how capable or productive a system is under those conditions, not how much of the input energy becomes useful output. It doesn’t quantify energy use versus output, which is what efficiency measures.

The rate at which energy is converted to heat refers to losses or dissipation, not the overall efficiency of turning input energy into useful work.

The amount of time required to complete a task is simply duration, not a measure of energy conversion effectiveness.

So the precise definition aligns with the ratio of useful output to input energy.