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Question
An electric lamp A of 40 W and another electric lamp B of 100 W are connected to 220 V supply. Calculate the ratio of their filament resistances?
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Solution
P = `"V.I" = "V.V"/"R"`
`40 = (220)^2/"R"_"A"`
RA = `(220 xx 220)/40`
RA = 110 × 11
P = `"V"^2/"R"`
`100 = (220)^2/"R"_"B"`
`"R"_"B" = (220 xx 220)/100`
RB= 22 × 22
`"R"_"A"/"R"_"B" = (110 xx 11)/(22 xx 22) = 5/2 = 5 : 2`
`"R"_"A"/"R"_"B" = 5: 2`
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