Electrical Resistivity and Electrical Conductivity
A filament bu...
Question
A filament bulb (500W100V) is to be wed in a 230V main supply. When a resistance R is connected in series, it works perfectly and the bulb consumes 500W. The value R is
A
26Ω
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B
13Ω
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C
230Ω
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D
46Ω
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Solution
The correct option is A26Ω Resistance of the bulb, R1=V2P = 100×100500 = 20Ω
It is connected in series with R, equivalent resistance = 20+R
Power consumed by the bulb, P=I2×R1 ⇒500=(23020+R)2×20 ⇒(20+R)2=(23)2×4 ⇒20+R=23×2=46 ∴R=26Ω