On an electric stove with a thermal power of 600 W with an efficiency of 45%, 1.5 kg

On an electric stove with a thermal power of 600 W with an efficiency of 45%, 1.5 kg of water with an initial temperature of 20 ° C was heated to boiling, and part of the water 5% turned into steam. How long did this process take?

Data: N (heat output of the hotplate) = 600 W; η (efficiency) = 45% (0.45); m (mass of water) = 1.5 kg; t0 (initial temperature) = 20 ºС; m1 (mass of water converted to steam) = 0.05m.

Constants: C (specific heat capacity) = 4200 J / (kg * K); tк (boiling point) = 100 ºС; L (beats heat of vaporization) = 2.3 * 10 ^ 6 J / kg.

η = (C * m1 * (tk – t0) + L * m2) / (N * t) and t = (C * m1 * (tk – t0) + L * 0.05 * m1) / (η * N ) = (4200 * 1.5 * (100 – 20) + 2.3 * 10 ^ 6 * 0.05 * 1.5) / (0.45 * 600) = 2506 s ≈ 42 min.