How long does it take to heat 500 g of water in a glass from 20 to boiling water using a 500 W electric boiler?

Data: P (boiler power) = 500 W; m (mass of heated water) = 500 g = 0.5 kg; t0 (initial water temperature) = 20 ºС.

Reference data: tboil (boiling water temperature) = 100 ºС; C (specific heat of water) = 4200 J / (kg * K).

1) Determine the required thermal energy for heating water: Q = C * m * (tboil – t0) = 4200 * 0.5 * (100 – 20) = 168000 J.

2) Let’s calculate the water heating time: Р = Q / t, whence t = Q / Р = 168000/500 = 336 s = 5 min 36 s.

Answer: You can heat water in 5 minutes 36 seconds.