Power: Where Energy Gets Real

Ohm's Law has a partner: the power equation. Power (measured in watts) tells you how much energy a circuit uses per second. The basic formula is P = IV — current times voltage.

This is why your electricity bill exists. A 100-watt bulb running for 10 hours uses 1 kilowatt-hour of energy, and your power company charges per kWh. A typical US household uses about 860 kWh per month — enough to run that 100-watt bulb nonstop for nearly a year (about 360 days).