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Question
Two bulbs are rated 60 W, 220 V and 60 W, 110 V respectively. Calculate the ratio of their resistances.
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Solution
Given,
Voltage, V1 = 220 V
V2 = 110 V
Power, P1 = P2 = P = 60 W
As R = `"V"^2/"P"`
`"R"_1 = "V"_1^2/"P" = (220 xx 220)/60`
`"R"_2 = "V"_2^2/"P" = (110 xx 110)/60`
On dividing R1 and R2
`"R"_1/"R"_2 = ((220 xx 220)/60)/((110 xx 110)/60)`
= `4/1`
`"R"_1 : "R"_2 = 4 : 1`
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