Question

a heater coil connected to a 220 v has a resistance of 150 ohms how long will it take for this coil to heat 1 kg from 20deg c to 60deg c assuming that all the heat is taken up by water

Answer 1

Heat produced per second or the power of the heater coil is, P = V²/R = 220²/150 = 322.67 W

Specific heat of water is, S = 4186 j/kg

So, heat required to raise the temperature of 1 kg water from 20 ^oC to 60 ^oC is,

H = mSθ = (1)(4186)(60 - 20) = 167440 J

So, time taken is found as,

H = Pt

=> t = H/P = 518.92 J