Paper 4 Current Electricity Fundamentals Drills

Q1 Resistivity experiment

A student measures resistance of wires of the same material but different lengths.

1. State the graph to plot to determine resistivity. [2]
2. State how resistivity is found from the gradient. [2]
3. State two precautions to reduce error. [2]

Q2 Internal resistance graph

A student varies an external resistance and records terminal p.d. $V$ and current $I$ for a cell.

$I/\mathrm{A}$	0.10	0.30	0.50	0.70	0.90	1.10
$V/\mathrm{V}$	1.54	1.45	1.37	1.29	1.20	1.12

1. Plot $V$ against $I$ and draw a best-fit straight line. [5]

2. Use the graph to determine the emf of the cell. [2]
3. Use the graph to determine the internal resistance. [2]
4. Explain why the current should not be too large and readings should be taken promptly. [2]
5. Suggest how a voltmeter zero offset would affect the derived emf and internal resistance. [2]