Question

A bulb consumed $24	ext{ J}$ of energy per second, when connected to a $12	ext{ V}$ supply. Calculate the power consumed when it is connected to a $6	ext{ V}$ supply.

Accepted Answer

1. Initial power $P_1 = 24	ext{ J/s} = 24	ext{ W}$ at $V_1 = 12	ext{ V}$. 2. Resistance $R = \frac{V_1^2}{P_1} = \frac{12^2}{24} = \frac{144}{24} = 6\ \Omega$. 3. At $V_2 = 6	ext{ V}$, power $P_2 = \frac{V_2^2}{R} = \frac{6^2}{6} = 6	ext{ W}$.

Power consumed by bulb at reduced voltage

Explanation

Practise this under board exam conditions