Question

A $100\text{W}$ bulb is designed to operate at a potential difference of $230\text{V}$. Find the current drawn by the bulb if it is operated at a potential difference for which it is designed.

• A. $\frac{2}{23}\text{A}$
• B. $\frac{5}{23}\text{A}$
• C. $\frac{7}{23}\text{A}$
• D. $\frac{10}{23}\text{A}$

Answer 1

The correct option is D $\frac{10}{23}\text{A}$

Given:
Power rating of the bulb, $P_o=100\text{W}$
Voltage rating of the bulb, $V_o=230\text{V}$

Resistance of the bulb will be

$R=\frac{V_0^2}{P_o}=\frac{(230{)}^2}{100}=529\Omega$

Since it is operated at rating voltage. So current drawn by the bulb

$I=\frac{V_o}{R}=\frac{230}{529}=\frac{10}{23}\text{A}$

Therefore, option $\left(d\right)$ is right.

Why this question ? Key concepts: $\text{Power rating}=\frac{\text{(Voltage rating}{)}^2}{\text{Resistance}}$