n identical light bulbs, each designed to draw P power from a certain supply, are joined in series across that supply. The total power which they will draw is

Let R be the resistance of each bulb. Resistance of n bulbs = n RCurrent in each bulb =i=VnRPower drawn by each bulbP2=i2R=V2n2R2×R=V2n2R=Pn2 ∵R=V2PTotal power drawn =n×Pn2=Pn