Which term is defined as Output divided by Input (times 100%)?

• A. Perpetual Motion Machines
• B. Conductors
• C. Insulators
• D. Efficiency

Answer: (D)

Efficiency is the ratio of useful output to input, expressed as a percent. Output divided by Input times 100% tells you how much of the input energy or effort actually becomes useful work. For example, if a machine uses 100 joules of energy and delivers 70 joules of useful work, its efficiency is (70/100) × 100% = 70%. In real systems, some energy is lost as heat, sound, or other forms, so efficiency is usually less than 100%. Perpetual motion machines describe devices that would violate energy conservation, so they’re not about how well energy is converted. Conductors and insulators describe electrical properties of materials, not the ratio of output to input. The term that fits is efficiency.