Question

An electric bulb rated as $40W,220V$. Calculate its resistance.

Answer 1

Step 1: Given data

Power, $P=40W$

Potential difference, $V=220volt$

Resistance of the bulb, $R=?$

Current flowing through the bulb, $I=?$

Step 2: Formula used

$I=\frac{P}{V}$ ……………………….(a)

$R=\frac{V}{I}$ ………………………(b)

Step 3: Calculation of the resistance of the bulb

Substituting the given values in equation (a), we get

$$\begin{gathered} I=\frac{40W}{220V} \\ I=0.1818A \end{gathered}$$

Substituting the value of the current obtained above and the given value of the potential difference in equation (b), we get

$$\begin{gathered} R=\frac{220V}{0.1818A} \\ R=1210\Omega \end{gathered}$$

Hence, the resistance of the bulb is equal to $1210\Omega$.