Question

The resistance of an electric heater is 50 Ω when connected to 120 V. How much energy does it use during 15 min of operation?

Answer 1

P(power) = I V = V^2 / R (V = I R Ohm's Law)

(I V = Q / t * V = Q / t * W / Q = W / t = power)

E = P * t = 120^2 / 50 * 15 * 60 = 259,200 Joules

(15 min = 60 sec/min * 15 min = 900 sec)