Question

In the given potentiometer circuit, length of the wire $\text{AB}$ is $3\text{m}$ and resistance $R=4.5\Omega$. The length $\text{AC}$ for no deflection in galvanometer is

• A. $2\text{m}$
• B. $1.8\text{m}$
• C. dependent on $r_1$
• D. none of these

Answer 1

The correct option is D none of these


From the diagram, we can easily observe that the cells in primary and secondary circuits are connected with reverse polarity. So, the balance point will not be obtained for any position on the entire length of wire $\text{AB}$.
Hence, option $\left(d\right)$ is correct.

Why this question ? Any potential difference which is less than the potential difference maintained across the potentiometer wire can be measured using potentiometer, but the battery should be placed in the right order.