Physics (AS & A Level) · Oct / Nov 2019 · Paper 12 · Question 34

Two cells with electromotive forces $E_1$ and $E_2$ and internal resistances $r_1$ and $r_2$ are connected to a resistor R as shown. The terminal potential difference across cell 1 is zero. Which expression gives the resistance of resistor R?

1. A$\dfrac{E_2 r_1 - E_1 r_2}{E_1}$
2. B$\dfrac{E_2 r_1 - E_1 r_2}{E_2}$
3. C$\dfrac{E_1 r_2 - E_2 r_1}{E_1}$
4. D$\dfrac{E_1 r_2 - E_2 r_1}{E_2}$

As printed in the paper