Power & watts

Power is how fast a component converts electrical energy into something else — light, heat or motion. It is measured in watts (W) and found with the simple formula P = V × I. A bigger number means energy is being used up faster.

Worked example: a device running at 5V and drawing 0.5A uses P = 5 × 0.5 = 2.5W. Combine P = V × I with Ohm’s Law and you get two more handy forms that don’t even need the current or voltage directly:

• P = I² × R
• P = V² / R

Power is also where electricity becomes heat. The current squared in P = I² × R is the warning sign: double the current and the heating quadruples. That’s why thin wires overheat long before fat ones — a thin wire has more resistance and far less surface to shed the heat, so the same current cooks it much faster.