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 consumes 500 W. The value of R is:
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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 consumes 500 W. The value of R is:

G1 Physics · Accepted Answer

Step 1: Bulb rated current I = P/V = 500/100 = 5 A. Step 2: Required drop across series resistor = 230−100 = 130 V. Step 3: R = 130/5 = 26 Ω.