Question

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

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

Answer 1

The correct option is A $10W$

Power of each bulb,

$P=40W$

Total power consumed when four bulbs are connected in series

$\frac{1}{P_s}=\frac{1}{P_1}+$ $\frac{1}{P_2}+\frac{1}{P_3}+\frac{1}{P_4}$

$\therefore$ $\frac{1}{P_s}=\frac{1}{P}+$ $\frac{1}{P}+\frac{1}{P}+\frac{1}{P}$

We get

$P_s=\frac{P}{4}$

$\Rightarrow P_s=\frac{40}{4}$

$\Rightarrow P_s=10W$