Question

An electric heater is used to heat 0.5kg of water in a kettle of heat capacity 400j/k, kept at 20degrees celsius.

what mass of water is boiled away in 600s? (Neglect heat losses)

Answer 1

The heat balance equation gives

$$Q=cm\Delta T+L\Delta m=P\tau$$

The mass of water that is boiled away

$$\Delta m=\frac{P\tau-cm\Delta T}{L}$$

$$\Delta m=\frac{2000*600-4200*0.5*80}{2.26*10^6}=0.46\:\rm kg$$