An electric bulb is rated as 220 V and 80 W. When it is operated on 110 V, the power rating would be :
80 W
60 W
40 W
20 W
Answer is Wrong!
Answer is Right!
This question was previously asked in
UPSC NDA-1 – 2023
– Power is proportional to the square of the voltage when resistance is constant (P ∝ V^2).
– Since the voltage is halved (110V is half of 220V), the power will be reduced by a factor of (1/2)^2 = 1/4.
– New Power = Rated Power * (New Voltage / Rated Voltage)^2 = 80 W * (110 V / 220 V)^2 = 80 W * (1/2)^2 = 80 W * (1/4) = 20 W.