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Question
A filament bulb (500w , 100 v) is to be used in 230v main supply . When resistance R is connected in series , it works perfectly and the bulb consumes 500w . The value of R is.
A filament bulb (500w , 100 v) is to be used in 230v main supply . When resistance R is connected in series , it works perfectly and the bulb consumes 500w . The value of R is.
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Solution
The resistance Rf of the filament lamp related to its power P and voltage V as
Rf = V^2/P = 100^2/500 = 20 Ω
The current through the filament lamp is P/V = 500/100 = 5 A
Since the main supply voltage is 230 volt and the total resistance in the series circuit is (20 + R) ohm, we have
230 volt/(20 + R) ohm = 5 ampere
Therefore (20 + R) = 46 from which R = 26 Ω
Rf = V^2/P = 100^2/500 = 20 Ω
The current through the filament lamp is P/V = 500/100 = 5 A
Since the main supply voltage is 230 volt and the total resistance in the series circuit is (20 + R) ohm, we have
230 volt/(20 + R) ohm = 5 ampere
Therefore (20 + R) = 46 from which R = 26 Ω
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