Required Practical: Investigating how the length of a wire affects resistance

Question 1

Describe the method for investigating how the length of a wire affects resistance. (8)

Answer 1

1. Set up the circuit as shown in the diagram.
2. Measure the length of the wire using a ruler. Make sure the wire is as straight as possible, and avoid parallax error by making sure your eyes are level with where you’re measuring the length.
3. Measure the p.d. using a voltmeter and the current using an ammeter. Use the switch momentarily to avoid the wire’s temperature increasing as the current causes a heating effect, which would increase the temperature of the wire and its resistance.
4. Repeat the process for six different lengths.
5. Determine the resistance of each length using R = V/I
6. Repeat the whole process again to check for anomalies, removing them before calculating a mean resistance.
7. Plot a graph of mean resistance on the y-axis and the length on the x-axis.
8. HAZARD: high currents may cause the wire to melt and burn the skin. Avoid this by using low currents.

Question 2

A student opened the switch between readings. Explain why this should be done. (3)

Answer 2

1. The current causes a heating effect in the wire.
2. This would cause the temperature of the wire to increase.
3. This would result in an increase in the resistance of the wire.