Q 12-03-232JEE MainJEE Main 2020 (2 Sep, Shift 2)Easy
A potentiometer wire $PQ$ of $1\ \text{m}$ length is connected to a standard cell $E_1$. Another cell $E_2$ of emf $1.02\ \text{V}$ is connected with a resistance $r$ and switch $S$ (as shown in figure). With switch $S$ open, the null position is obtained at a distance of $49\ \text{cm}$ from $Q$. The potential gradient in the potentiometer wire is:
Answer: (A) $0.02\ \text{V/cm}$
At the null point no current flows through $E_2$, so the resistance $r$ has no effect and the balancing length corresponds to the emf $1.02$ V:
$$k = \frac{1.02\ \text{V}}{49\ \text{cm}} \approx 0.02\ \text{V/cm}$$
Solution by Sreeraj P, M.Sc Physics