Question

The variation of potential difference $V$ with length $l$ in case of two potentiometers $P$ and $Q$ is as shown. Which one of these two will you prefer for comparing emfs of two primary cells ?

Answer 1

For greater accuracy of potentiometer, the potential gradient (slope) $\frac{V}{l}$ must be as small as possible.In the graph given the slope $\frac{V}{l}$ is smaller for a potentiometer Q: hence we shall prefer potentiometer Q for comparing the emfs of two cells.