Physics (AS & A Level) · May / June 2020 · Paper 11 · Question 36

A cell of electromotive force (e.m.f.) E and internal resistance r is connected to a resistor of resistance R. A maximum power P can be dissipated by the resistor without overheating. [circuit diagram showing cell E with internal resistance r in a dashed box, connected to external resistor R] What is the maximum value of E if the resistor does not overheat?

1. A$R\sqrt{\dfrac{P}{(R-r)}}$
2. B$R\sqrt{\dfrac{P}{(R+r)}}$
3. C$(R-r)\sqrt{\dfrac{P}{R}}$
4. D$(R+r)\sqrt{\dfrac{P}{R}}$

As printed in the paper