Electrical Power and Energy

$P = V I = I^2 R = \frac{V^2}{R}$

Example: 22.7 mA through 220 Ω dissipates $P = (0.0227)^2 \times 220 \approx 0.11$ W — fine for a ¼ W (0.25 W) resistor.

Energy is power multiplied by time: $E = P t$. Electricity bills use kilowatt-hours: 1 kWh $= 3.6 \times 10^6$ J.

Always check that each component's power rating comfortably exceeds what it will dissipate — a common rule is to use at least twice the calculated power.