First slide
Thermal effect of current
Question

Two electric bulbs rated P1 and P2 watt at V volt are connected in series across V volt mains, then their total power consumption P is:

Moderate
Solution

Resistance of Ist bulb =R1=V2P1

Resistance of IInd bulb =R2=V2P2

When both bulbs are connected in series,

Req.=V21P1+1P2=V2P1+P2P1P2

Hence, power consumed P=V2R

                                           =V2V2P1+P2P1P2=P1P2P1+P2

                                         Hence, (c) is correct.

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