Energy & your bill

It’s easy to mix up power and energy, so pin down the difference: power is the rate of using energy (how fast), while energy is power multiplied by time (how much in total). Run a 1-watt device for 1 second and it uses 1 joule of energy.

Think of power as your car’s speed and energy as the distance you travel. Going fast (high power) for a moment covers little ground; going slow for hours can cover a lot. Energy = how fast × how long.

Your electricity bill ignores joules — they’re too small — and uses the kilowatt-hour (kWh) instead: running 1000W for 1 hour. So a 100W bulb left on for 10 hours uses 100W × 10h = 1000 Wh = 1 kWh. The meter on your wall is literally counting kWh.