Q. An electric kettle takes 4 A current at 220 V. How much time will it take to boil 1 kg of water from temperature 20°C? The temperature of boiling water is 100°C.
A) 4.2 min
B) 6.3 min
C) 8.4 min
D) 12.6 min
Explanation
[Solution from source] Heat needed = mcΔθ = 1 × 4200 × 80 = 3.36 × 10⁵ J; power = VI = 220 × 4 = 880 W. t = 3.36 × 10⁵/880 ≈ 382 s ≈ 6.4 min, closest to 6.3 min. Heating from 0°C to 100°C instead of 20°C would give about 8 min. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.