2026 Current ElectricityElectrical power, $P = V^2/R$ Medium Question 5 of 130 in Current Electricity

A room heater is rated 400 W, 220 V. If the supply voltage drops to 200 V, what will be the power consumed (approximately)?

A 121 W
B 331 W
C 200 W
D 400 W

The answer is B.

Solution

Rated voltage = 220 V, rated power = 400 W, supply voltage = 200 V Resistance of heater $R_H = \frac{(220)^2}{400}$ Actual power $P' = \frac{V_s^2}{R_H} = \frac{(200)^2}{(220)^2} \times 400$ $= 330.57$ W $\approx 331$ W

Current Electricity in past papers

130 questions from this chapter have appeared across 27 exam years.