Question

An electric kettle is rated with a Power 2.2kw. It is filled with 1.5kg of water at 12°c as measured coming from the cold tap. We know that the specific heat capacity of water; 42008kg-¹K²1. Calculate theoretically it will take to boil the kettle in mins and seconds.

(b) You just realised that the kettle is made of copper. The weight if the kettle is 0.5kg. Determine how much energy it took to heat the Copper of the kettle. The Speciffic heat capacity of copper is 385Jkg - K​

Answer 1

(a) P = 2.2 kW = 2200 watts / sec power input

1 cal = 4.19 Joules

P = 2200 / 4.19 = 525 cal / sec power input

E = C M ΔT = 1 cal / (gm deg K) 1500 gm * 88 deg K = 132,000 cal input

E = P * t (power * time)

t = 132000 / 525 = 251 sec = 4.19 min to heat kettle

(b) 385 J / kg / (4.19 cal / J = 91.9 cal / (kg deg C) heat required for kettle

.5 kg * 88 deg C * 91.9 cal / (kg deg C) = 4044 cal heat kettle

t = E / P = 4044 cal / 525 cal /sec = 7.70 sec to heat kettle