Electrical Power, Energy Transfers & The National Grid

Electrical power

• The power transferred by a device depends on the potential difference across it and the current through it (recall both equations):

$$P = V I \qquad P = I^2 R$$

• $P$ power in W; $V$ in V; $I$ in A; $R$ in Ω
• Worked example: a 230 V kettle draws 10 A: $P = 230 \times 10 = 2300$ W
• Worked example: 3 A through 12 Ω: $P = 3^2 \times 12 = 108$ W
• Combining with $V = IR$: at fixed resistance, doubling the potential difference doubles the current, so the power is four times larger ($P = \dfrac{V^2}{R}$)