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Question:

Six similar bulbs are connected as shown in the figure with a DC source of emf E and zero internal resistance. The ratio of power consumption by the bulbs when (i) all are glowing and (ii) in the situation when two from section A and one from section B are glowing, will be

9:4

1:2

2:1

4:9

Solution:

Correct option is B.9:4(i) All bulbs are glowingReq=R3+R3=2R3Power(Pi)=E2Req=3E22R... (1)(ii) Two from section A and one from section B are glowing.Req=R2+R=3R2Power(Pf)=2E23R... (2)⟹PiPf=3E23R2R2E2=9:4