Question

# A filament bulb (500 W, 100 V) is to be used in a 230 V main supply. When a resistance R is connected in series, it works perfectly and the bulb consumes 500 W. The value of R is

A
26 Ω
B
13 Ω
C
230 Ω
D
46 Ω

Solution

## The correct option is D 26 Ω As in first case there is no resistance except the bulb so, the resistance of the bulb can be calculated as, Rbulb=V2P=1002500=20 Ω In second case the bulb and the resistance are in series, current remains same across them and the resistance of the bulb is also same, by using ohm's law V∝R    RRbulb=130100⇒R20=130100⇒R = 26 Ω

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