Question

Three incandescent bulbs of 100W each are connected in series in an electrical circuit. In another circuit another set of three bulbs of the same wattage are connected in parallel to the same source.
(a) Will the bulb in the two circuits glow with the same brightness? Justify your answer.
(b) Now let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason.

Answer 1

(a) No.
Reasons: Let R be the resistance of each bulb, then total resistance in series = 3R In series, current in each bulb is same.
So current drawn by each bulb connected in series is one third as compared to the current in each bulb in a parallel arrangement, so the bulbs connected in parallel combination glow more brightly.
(b) In a series arrangement, if one bulb is fused; then current in the bulbs connected in series will become zero, so bulbs will stop glowing. In a parallel arrangement, if one bulb is fused, the other two bulbs will continue to glow with same brightness.