6.6 Determining the Resistivity of a Wire

Question 1

How do you experimentally find out the cross-sectional area of a test wire?

Answer 1

• measure the diameter of the wire in at least 3 different places along the wire using a micrometer
• find the mean diameter and use this to find out the cross sectional area

Question 2

How do you experimentally measure resistivity?

Answer 2

1. Set up a circuit with a power supply, ammeter, a ruler, the test wire and a voltmeter (around the test wire)
2. Measure the length of the wire
3. Measure the current through the circuit and the potential difference across the test wire. Use these values to calculate the resistance.
4. Repeat this process at least 1 more time and calculate the mean resistance for this length of the wire
5. Reposition the crocodile clips to vary the length of wire, and repeat.

Question 3

How do you find resistivity from a graph of resistance against length?

Answer 3

Multiply the gradient by the cross sectional area