Dr Andrew French. October 2020.
TEACHER NOTES
lR
A
=
Equipment
Digital calliper(for measuring wirediameter)
Wooden mounting rigwith metre ruler attached
Electrodes(with electrically insulated handles)
2V DC power supply
1.00m of steelwire stretchedbetween terminalsWire terminals
Ammeter
Voltmeter
Steel wire
Place the wire between the jaws of the digital calliper to measure the diameter.
Don’t forget to zero the calliper (when closed) first!
I measured: ( )0.29 0.1 mmd =
Measure the potential difference between afixed separation of wire. Using two electrodes connected to the voltmeter
Note if you use a single electrode, you need to be careful about the contact resistance of therest of the circuit. So using two electrodes is preferable.
https://hypertextbook.com/facts/2006/UmranUgur.shtml
https://hypertextbook.com/facts/2006/UmranUgur.shtml
Circuit schematic
Steel wire of diameter d
If we plot V vs d then we should get a straight line from the origin. From the gradient we can findthe resistivity .
( )
2
23
7
4
1.6105 1.6105
0.29 10 1.6105
4 0.1173
9.07 10 Ωm
V kl
d k
I
V l k
−
−
=
=
= =
=
=
Which appears to be a plausible result
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