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Question
A. bulb is rated at 100W, 250V and another one at 60W, 250V. What is the current flowing in the circuit if the two bulbs are put in series across a 220 V mains supply?
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Solution
The resistance of first bulb = `"V"^2/"P"_1 = (250 xx 250)/100` Ω = 625 Ω
Resistance of second bulb = `"V"^2/"P" = (250 xx250)/60` Ω = `3125/3` Ω
∴ Resistance of the circuit containing the two bulbs in series
`= (625 + 3125/3) Omega = 5000/3 Omega`
∴ Current flowing `= 200 div (5000/3)`A
`=(220 xx 3)/5000` A `= (220 xx 3)/5000 xx 1000 "mA" = 132 "mA"`
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