**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)**

(b)

(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)**