Suppose that 600 W of radiation in a microwave oven is absorbed by 250 g of water in a very lightweight cup. Approximately how long will it take to heat the water from 20 C to 80 C?

(A) 50 s

(B) 100 s

(C) 150 s

(D) 200 s

option (B)

Explanation:

Power, P = 600 W

mass of water, m = 250 g = 0.250 kg

T1 = 20° C

T2 = 80° C

ΔT = 80 - 20 = 60

specific heat of water, c = 4200 J/kg °C

Let the time taken is t.

Power x time = mass of water x specific heat of water x rise in temperature

600 x t = 0.250 x 4200 x 60

t = 105 second

option (B)