Required Pracical 5: Determination Of Resistivity Of A Wire

Question 1

Describe a method to determine the resistivity of a wire

Answer 1

1) measure the diameter of the constantan wire at 5 different points along the wire and calculate a mean
2) set up the apparatus
3) tape the wire to the ruler with one end of circuit attached to wire at 0m
4) adjust the length to 0.1m using a crocodile clip flying lead
5) set the power supply to 6V
6) record the current and voltage using ammeter and voltmeter
7) calculate R using V/I = R
8) switch off current between readings so the wire doesn’t get too hot
9) vary the distance in 0.1m intervals up to 0.8m
10) repeat experiment twice and record mean R for each I
11) calculate cross sectional area of wire
12) plot a graph for mean R against I and draw a line of best fit
13) the resistivity is the gradient x A

Question 2

What is the independent variable

Answer 2

The length of the wire

Question 3

What is the dependant variable

Answer 3

The current through the wire

Question 4

List some control variables

Answer 4

• voltage through the wire
• the material the wire is made from

Question 5

What safety considerations are there

Answer 5

• don’t touch wire when circuit is on as it will be hot

Question 6

How can you reduce uncertainty in the experiment

Answer 6

• disconnect circuit between measurements so wire doesn’t heat up and resistance doesn’t change
• made sure end of wire is attached at 0cm so there isn’t a zero error