Question

three incandescent bulbs of 100 watt eachare connected in series in an electric circuit in another circuit another set of three bulbs of same wattage are connected in parallel to the same source.
Will the bulb in the circuit glow with the same brightness? justify.

Answer 1

Answer:
1. No the bulbs won't glow with the same brightness in both circuits. The bulb in parallel circuit will glow brighter than when connected in series.
Power of each bulb (P) = 100W at 220V
Hence, Resistance of each bulb (R) = V^2/P

Now, when they are connected in series,
Req = R+R+R = 3R
Let the source voltage be V'
hence, I = V'/3R
Hence, power through each bulb = I^2R = V'^2/9R

In Parallel, bulbs are connected to the same source i.e. voltage = V'
Hence, power through each bulb = V'^2/R

Since brightness is directly proportional to power, hence bulbs when connected in parallel would glow brighter.

2. In series connection, if one bulb fuses, then the circuit would break and no current would flow. So, none of the other 2 bulbs will glow.

However, in the parallel connection, if one bulb fuses, the current would still be able to flow through the other arms and hence the remaining 2 bulbs will glow.

Answer 2

Answer:

(a) .

Ans. Voltage gets divided in series combination. So bulbs in series combination will glow with less brightness. Voltage does not get divided in parallel combination, so bulbs in parallel combination will glow with more brightness.

(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.

Ans. In case of series combination, fault in even a single component will break the circuit.

So, when one of the bulbs gets fused: another bulb would continue to glow.