Question

An electric immersion heater is switched on for 8 minutes. The heat supplied by it raises the temperature of 500 g of water from 10°C to 60°C. Calculate the power of the heater in watts.

[Specific heat of water = 4.2 Jg⁻¹°C⁻¹]

Answer 1

Time = 8 min = 480 s

Let the power of the heater = P

Energy supplied by the heater = P × t = P × 480 s

Also, rise in temperature of water θ_R = (60 − 10) = 50°C

∴ Heat energy absorbed by water = mcθ_R

= 500 g × 4.2 Jg⁻¹°C⁻¹ × 50°C

= 105000 J

∴ By the law of conservation of energy,

P × 480 s = 105000 J

\[\therefore P =\frac{105000}{480}\]

= 218.75 J/s

= 218.75 W