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Question
Two exactly similar electric lamps are arranged (i) in parallel, and (ii) in series. If the parallel and series combination of lamps are connected to 220 V supply line one by one, what will be the ratio of electric power consumed by them?
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Solution
Let R be the resistance of the lamp and V be the potential difference applied.
In a series connection:
Net resistance of the circuit, R1 = R + R = 2R
Power drawn, P1 = V2/R1 = V2/2R
In a parallel connection:
Net resistance of the circuit, R2 will be:
`1/R_2=1/R+1/R=2/R` or `R_2=R/2`
Power drawn, P2 = V2/R2 = 2V2/R
Therefore, P2:P1 = 4:1
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