Physics (AS & A Level) · Oct / Nov 2023 · Paper 13 · Question 37

A potentiometer and a driver cell of electromotive force (e.m.f.) E are used to measure the e.m.f. of a new cell. A sliding contact at P is moved along a resistance wire QR until the reading on the galvanometer is zero. [circuit diagram: driver cell E connected across resistance wire QR; sliding contact P on wire QR connected through a galvanometer to a new cell] What is an essential requirement for the e.m.f. of the new cell to be measured accurately?

1. AThe e.m.f. of the driver cell must be less than the e.m.f. of the new cell.
2. BThe galvanometer must have a large resistance.
3. CThe internal resistance of the new cell must be zero.
4. DThe resistance per unit length of the wire QR must be constant.

As printed in the paper