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Resistance of a Wire

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Resistance of a wire investigation


To find out which variables affect the resistance of a wire.


In this investigation I will try to find out what variables affect the resistance of a wire.  I can do this by trying various different variables such as:

  • Length of Wire
  • Voltage Setting
  • Type of Wire
  • Shiny or not Shiny
  • Diameter of Wire
  • Temperature


The variable I have chosen for my final experiment is the diameter of a wire.  This is because it should have good results due to the fact the when diameter decreases, the area for current to flow decreases.  It is much like chicken going through a gate.  If the gate is slightly open (small diameter), it takes longer for the chickens (electrons) to go through and less can go through, where as, if it is fully open (large diameter) then more chickens (electrons) can pass through.


I will test my theory that as the diameter increases, the resistance decreases as my final experiment.  I will have to do a set of preliminary experiments first so I can see which length of wire, voltage setting

To work out the resistance of a wire I will have to use Ohm’s law.

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30 cm




35 cm




40 cm




45 cm




From these results I have decided that the wire length I will use is 15cm.  This is because it has reasonable answers that are not at extremes.  Also, at 15cm, the wire was at a sensible temperature and didn’t glow due to extreme temperatures.

Final Experiment

For the final experiment I will be testing the diameter of wires.  I will have to use analogue meters and a screw gauge micrometer to test the different parameters.

Screw Gauge Micrometer


The screw gauge micrometer is a very delicate instrument.  It can measure objects to the 100th of a millimetre, that’s a 1000th of a cm.  It can be very difficult to read at first but once you know how to read it its very easy.

First of all you put the object you want to measure in between the anvil and the spindle.  You then turn the thimble until it is finger tight.  Then you turn the ratchet clockwise until it clicks once.

Then you have to work out the size of the object.  On the sleeve it has a scale.  The top line is 0.0mm, 1.0mm, 2.0mm, 3.0mm etc.  The bottom line is 0.5mm, 1.5mm, 2.5mm, 3.5mm etc.  The diagram above is 6.

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I feel that most of my results were accurate.  However, the accuracy of the power output from the power packs was generally inaccurate, but at a constant rate.  

Looking at my graph I can see that there were differences each time I carried out the experiment as the resistance was different each time, the largest difference in resistance was at the 2-3mm thick wire diameter.  I feel that this could be due to the wire heating up and thus increasing the resistance as I did not allow sufficient time for the wire to cool down to its original temperature.

I feel that If I was to carry out the experiment again I would find out the resistance of the connecting banana leads as these have their own resistance rendering the experiment unreliable.  I would also make sure that the wire being tested was held and clamped in a straight line to insure that no resistance can be incurred from the wire being bent.  However, I feel that bearing in mind the equipment I had available, the experiment was a success and reliable.

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