Questions on EMF and internal resistance

Q10. A cell of emf, ε, and internal resistance, r, is connected to a variable resistor R. The current through the cell and the terminal pd of the cell are measured as R is decreased. The circuit is shown below.

The graph below shows the results from the experiment.

(a) Explain why the terminal pd decreases as the current increases.

(2 marks)


(i) Use the graph to find the emf, ε, of the cell.

(1 mark)

(ii) Use the graph above to find the internal resistance, r, of the cell.

(3 marks)

(c) Draw a line on the graph above that shows the results obtained from a cell with

(i) the same emf but double the internal resistance of the first cell labelling your graph A.

(2 marks)

(ii) the same emf but negligible internal resistance labelling your graph B.

(1 mark)

(d) In the original circuit shown in part (a), the variable resistor is set at a value such that the current through the cell is 0.89 A.

(i) Calculate the charge flowing through the cell in 15 s, stating an appropriate unit.

(2 marks)

(ii) Calculate the energy dissipated in the internal resistance of the cell per second.

(2 marks)

(Total 13 marks)