Efficiency is a measure of how well a device or system converts input energy into useful output energy. It tells us how much of the energy we put in is actually used for the intended purpose, and how much is wasted (often as heat or sound).

Formula:Efficiency = (Useful energy output ÷ Total energy input) × 100%

Example:If a machine receives 200 joules of energy and delivers 150 joules as useful work, the efficiency would be:(150 ÷ 200) × 100% = 75%

No machine is perfectly efficient—there is always some energy loss in real systems.

Examples:

• Car Engines: A petrol engine may only be about 25–30% efficient—most energy is lost as heat.

• LED Bulbs: Much more efficient than filament bulbs because more of the input energy becomes light, not heat.

• Electric Motors: Often over 90% efficient, which makes them ideal for modern appliances and machines.

Why Is Efficiency Important?

• Reduces Wasted Energy: The more efficient a system, the less energy is lost as heat, sound, or vibration.

• Saves Cost: More efficient machines use less energy for the same amount of work, which reduces electricity or fuel bills.

• Environmental Impact: Less wasted energy means fewer resources burned, so it’s better for the planet.

• Improves Performance: Efficient systems run smoother and often last longer.