Question

Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another circuit another set of three bulbs of the same wattage are connected in parallel to the same source.

1. Will the bulb in the two circuits glow with the same brightness? Justify your answer.
2. 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

Bulbs connected in series	Bulbs connected in parallel

Let us assume that the resistance of each bulb is R.
In series: 
Current in each bulb = `"V"/(3"R")`
In Parallel:
Net current =`(3"V")/"R"`
Current will get equally divided in three bulb `= "I"/3 = "V"/"R"`

1. In a series combination, the potential difference gets divided, whereas, in parallel, the potential difference across each bulb remains full. Hence, in series, bulbs glow with less brightness than bulbs in parallel connection. 
2. Now, if one bulb gets fused in a series connection, all the other bulbs will stop glowing, whereas in a parallel connection, other bulbs will continue to glow. This is because in a series combination, even a single faulty component breaks the circuit, whereas this does not happen in a parallel circuit.