What is the term for the ratio of output power to input power, generally expressed as a percentage?

• A. Power factor
• B. Efficiency
• C. Voltage regulation
• D. Load factor

Answer: (B)

Efficiency is the ratio of useful output power to the input power, usually expressed as a percentage. It shows how much of the incoming energy is converted into the desired form rather than lost as heat or other losses. In practice, you compare Pout to Pin: η = (Pout / Pin) × 100%. For example, if a device draws 1000 watts and delivers 850 watts of useful output, its efficiency is 85%. Higher efficiency means fewer losses and better performance. Other terms describe different ideas: power factor deals with how well current and voltage waveforms align in AC circuits; voltage regulation refers to how much the output voltage changes from no-load to full-load; and load factor describes how consistently the system is used over a period.