PYQ NEET- Current Electricity L-3

Question: The emf of a cell having internal resistance $1 \Omega$ is balanced against a length of $330 \mathrm{~cm}$ on a potentiometer wire. When an external resistance of $2 \Omega$ is connected across the cell, the balancing length will be : (2023)#

A) $220 \mathrm{~cm}$

B) $330 \mathrm{~cm}$

C) $115 \mathrm{~cm}$

D) $332 \mathrm{~cm}$

Answer: $220 \mathrm{~cm}$#

Explanation#

$\begin{aligned} & \mathrm{r}=\left(\frac{\ell_{\mathrm{o}}-\ell_{\mathrm{c}}}{\ell_{\mathrm{c}}}\right) \mathrm{R} \ & 1=\left(\frac{330-\ell_{\mathrm{c}}}{\ell_{\mathrm{c}}}\right) \times 2 \ & 3 \ell_{\mathrm{c}}=660 \ & \ell_{\mathrm{c}}=220 \mathrm{~cm}\end{aligned}$