Physics (AS & A Level) · Feb / March 2021 · Paper 12 · Question 36

A cell that has internal resistance is connected to a switch S and a variable resistor. A voltmeter is connected between the terminals of the cell, as shown. When switch S is open, the voltmeter reads 1.5 V. The switch is then closed and the variable resistor is adjusted to have a resistance of 4.0 Ω. The voltmeter now reads 0.75 V. What is the internal resistance of the cell?

1. A1.0 Ω
2. B2.0 Ω
3. C4.0 Ω
4. D8.0 Ω

As printed in the paper