Question

An immersion heater rated 1000W, 220V is used to heat 0.01m³ of water. Assuming that the power is supplied at 220V and 60% of the power supplied is used to heat the water, how long will it take to increase the temperature of the water from 15°C to 40° C?

Answer 1

P = 1000

V = 220v

R = V²/P = 48400/1000 = 48.4Ω

Mass of water = 1/100 x 1000 = 10kg

Heat required to raise the temp. of given amount of water = msΔt = 10 × 4200 × 25 = 1050000

Now heat liberated is only 60%. So V²/R x T x 60% = 1050000

=> (220)²/48.4 x 60/100 x T = 1050000 => T = 10500/6 x 1/60nub = 29.16min