Physics (AS & A Level) · Oct / Nov 2024 · Paper 13 · Question 35

The diagram shows part of a circuit that uses a potentiometer wire to measure a potential difference (p.d.) in an external circuit. The potentiometer wire XZ has length L1. It is connected to a cell of known electromotive force (e.m.f.) E that has negligible internal resistance. Terminals P and Q are connected to the external p.d. to be measured. The length of the potentiometer wire between points X and Y is L2. The ratio of the lengths L1 and L2 is used to determine the p.d. between P and Q in terms of E. Which condition must be met in order to determine this p.d.?

1. AThe current I1 must be zero.
2. BThe current I2 must be zero.
3. CThe p.d. across YZ must be zero.
4. DThe resistance of the external circuit must be zero.

As printed in the paper