Three incandescent bulbs of 100W

Question:

Three incandescent bulbs of 100W each are connected in series in an electric circuit. In another circuit, another set of three bulbs of the same voltage

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.

(CBSE 2012)

Solution:

(a) Power dissipated in a circuit = V2/R. Since resistance of the circuit containing bulbs connected in series is more than the resistnace of the

circuit containing bulbs in parallel, therefore, power dissipated in parallel combination is more than that in series combination. Hence, bulbs

connected in parallel will glow more brightly.

(b) In series combination, there is only one path for the flow of current. So when one bulb gets fused, circuit is broken and hence the bulbs stop

glowing.

In parallel combination, each bulb has its own path for the flow of current. So when one bulb gets fused, other bulbs will continue to glow as the

current is flowing in the circuits of these bulbs.

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