Question

In the following figure, grade the bulb in order of their brightness.

• A. $B_3>B_2>B_1$
• B. $B_1>B_2>B_3$
• C. $B_3>B_1>B_2$
• D. $B_2>B_1>B_3$

Answer 1

The correct option is A $B_3>B_2>B_1$

We know that resistance of bulb is given by :

$R=\frac{V_{rated}^2}{P_{rated}}$

For all bulbs, rated voltage is same. So, resistance is inversely proportional to the rated power.

$\therefore R_3>R_2>R_1$

Since all bulbs are in series, so current through them will be same. And power consumed by bulb will be

$P=i^{2}R$

$P\propto R(\because i=\text{constant})$

Since, we know that brightness is proportional to the power consumed.

$\therefore$ Brightness order is $B_3>B_2>B_1$

So, the right option is $\left(a\right)$.
$$\begin{array}{c}\text{Why this question ?}\\ \text{Tip: In series connection bulb with high}\\ \text{resistance glow with more brightness.}\end{array}$$