Question

An electric kettle is rated 1500 W. Calculate the time in which it will bring 1.5 kg of water at 25°C to its boiling point.

[Take specific heat capacity of water = 4200 J kg⁻¹ K⁻¹]

Answer 1

Given:

Power rating (P) = 1500 W (or 1500 J s⁻¹)

Mass of water (m) = 1.5 kg

Initial temperature (T₁) = 25°C

Final temperature/Boiling point (T₂) = 100°C

Rise in temperature (ΔT) = 100°C − 25°C = 75°C (or 75 K)

Specific heat capacity of water (c) = 4200 J kg⁻¹ K⁻¹

Q = mcΔT

= 1.5 × 4200 × 75

= 4,72,500 J

Energy Supplied = Power × Time

4,72,500 = 1500 × t

t = `(4,72,500)/1500`

t = 315 seconds

Convert time into minutes:

t = `315/60`

= 5 minutes and 15 seconds