物理 heat

Specific latent heat of fusion of water, lf = 3.34 X 105 Jkg-1

Specific heat capacity of water, c = 4200 Jkg-1*C-1

Mass of water, m = 0.5 kg

Temperature change of water, T = 100 *C


Energy required to heat the ice to boiling water, E

= mlf + mcT

= 0.5(3.34 X 105 + 4200 X 100)

= 377 000 J

This is the energy output of the heater.

Energy input of the heater, E'

= energy output / efficiency

= 377 000 / (1 - 30%)

= 5.39 X 105 J

Time required, t

= E' / P

= 5.39 X 105 / 500

= 1077 s

= 17.95 mins