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Question

An electric bulb is rated 220 V and 100 W. When it is operated at 110 V, the power consumed will be



A
100 W
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B
75 W
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C
50 W
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D
25 W
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Solution

The correct option is B 25 W

Power consumed by the electric bulb, P=V2R, where V is the potential difference and R is the electrical resistance.
Given for 1st case:
Voltage V1=220 V
 and power consumed by bulb P1=100 W,
In the 2nd case:
Voltage of the bulb, V2=110 V
Power consumed by the bulb = P2
Since the resistance is the same as it is the same bulb
P1P2=(V1)2(V2)2
100P2=(220)2(110)2
P2=100×(110)2(220)2=25W
Power consumed when the bulb is operated at 110V = 25W


Physics

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