Question

An electric bulb is rated 240 V- 60W and is working at 100% efficiency.

Calculate the resistance of the bulb.

Answer 1

Step 1- Given data-

Power rating $P=60W$

Potential difference $V=240V.$

Step 2- To find out the resistance of the bulb-

The formula for power delivered is $P=\frac{V^2}{R}$, where R is the resistance of the bulb.

Thus, $R=\frac{V^2}{P}$

$$\begin{gathered} \Rightarrow R=\frac{{\left(240\right)}^2}{60} \\ \Rightarrow R=960\Omega \end{gathered}$$

Thus, the resistance of the bulb is $960\Omega$