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Question:

Two electric bulbs, rated at (25 W, 220 V) and (100 W, 220 V), are connected in series across a 220 V voltage source. If the 25W and 100 W bulbs draw powers P1 and P2 respectively then__________?

P1=4W,P2=16W

P1=16W,P2=9W

P1=9W,P2=16W

P1=16W,P2=4W

Solution:

R1 = (220²)/25 = 1936 Ω
R2 = (220²)/100 = 484 Ω
i = 220/(R1 + R2) = 220/(1936 + 484) = 11/111 A
P1 = i²R1 = (11/111)² × 1936 = 16 W
P2 = i²R2 = (11/111)² × 484 = 4 W