Question

A heater, rated 1000 W, is used to heat 1.5 kg of water at 40°C to its boiling point. Calculate the time in which the water starts to boil. Specific heat capacity of water is 4200 Jkg⁻¹°C⁻¹.

Answer 1

Mass of water, m = 1.5 kg

Rise in temperature, ΔT = 100 − 40 = 60°C

Specific heat capacity of water = 4200 Jkg⁻¹°C⁻¹

Heat required: Q = mcΔT

= 1.5 × 4200 × 60°C

= 378000 J

Heater power, P = 1000 W

$$P=\frac{Q}{t}$$

$$t=\frac{Q}{P}$$

$$=\frac{378000}{1000}$$

= 378 s