The variation of potential difference V with length l in the case of two potentiometers A and B are as shown in the figure. Which one of these two will you prefer for comparing emf of two cells and why?

A potentiometer is called sensitive if fall of potential per unit length ie potential gradient is small. The slope of V-l graph gives potential gradient which is smaller for the potentiometer wire B than for potentiometer wire A. Hence, potentiometer wire B is more sensitive.

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