Which unit is used to measure energy?

• A. Watt.
• B. Newton.
• C. Volt.
• D. Joule.

Answer: (D)

Energy is measured in joules. A joule is defined as the work done when a force of one newton moves an object one meter in the direction of the force, which ties energy directly to work. This is why joules are the natural unit for energy—the total amount of energy available or transferred is quantified in joules, while work describes that transfer. A watt, by contrast, is a unit of power—the rate at which energy is transferred or consumed—so it isn’t a measure of energy itself. A newton measures force, and a volt measures electric potential difference. In everyday terms you’ll also see kilojoules or kilowatt-hours used, with 1 kilowatt-hour equaling 3.6 million joules, and 1 watt equaling 1 joule per second, linking energy to the rate of use.