Question

Four bulbs marked 40 W, 250 V are connected in series with 250 V mains, the total power consumed is

• A. 10 W
• B. 40 W
• C. 320 W
• D. 160 W

Answer 1

The correct option is A 10 W

Answer is A.

If n identical bulbs of the same power are connected in series, to the constant voltage, the drop across each bulb is $\frac{V}{n}$.
So, the power consumed by each bulb is $\frac{P}{n^2}$.
Total power consumed by n such bulbs is given as $n\times \frac{P}{n^2}=\frac{P}{n}$.

In this case, there are 4 identical bulbs of power 40 W connected to 250 V of supply.
The total power consumed by 4 such bulbs is $\frac{40}{4}=10W.$
Hence, the total power consumed is $10W.$