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How will the length of wire effect the resistance?

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Arjan Thethy 10.T          Physics Coursework        Dr Redman

How will the length of wire effect the resistance?

Skill Area P: Planning experimental procedures:

As we are looking at the factors affecting the resistance of a wire, the first decision is to investigate the various variables of wire.  Length, thickness, shape and type of metal used.  

Only one variable is chosen. Varying the length is the easiest method in which to measure the resistance of a wire.  The remaining variables should be kept constant.  Thickness is measured in SWG’s of: 28, 30, 32, 34 and 36. 28swg’s is a substantial thickness of wire as it still allows the flow of electrons to pass through.  The shape of the wire can be changed by twisting, curling or disfiguring it in some way.  Keeping it straight will give more accurate results.  The type of metal chosen is very important; the two choices are Copper and Constantan.  Copper is a very good conductor of electricity, so would not be good to use in an investigative experiment, as the readings would be too low and therefore would not produce defining results therefore it is best to use Constantan.

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This statement can help to predict the fact that as the length of wire increases the resistance increases. If you double the length of wire, the amount of atoms double which means it will take double the time for the electrons to flow through the wire. The diagram below helps explain this.

The electrons in the longer wire will obviously take longer to get past the atoms than in the shorter wire.

Set up:

We set up the experiment just as shown below.


Constantan wire

Preliminary results.

Before doing the proper results, we did a preliminary test to see how much we should change the wire after each result. We decided on 5cm because we found that there was a substantial change but not too much so this meant that we could get a good graph and a good set of results.


The test showed that the results are consistent and that the gap is enough to see a substantial difference.

Skill area O: Obtaining evidence

This is the method that will be carried out to connect the circuit and achieve the specified results:

  • Connect the apparatus to form the circuit, as shown on page 2.
  • The wire (Constantan) should be sellotaped to a meter rule to keep it straight; this allows the flow of electrons to pass easily and without blockage.
  • Connect the crocodile clips at either end of the 50cm length of wire.
  • Take the reading of the ohmmeter.
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When the wire wasn’t connected, I found that there was still a slight reading on the Ohmmeter it always read 0.2. This is because the crocodile clips had a slight resistance.

Skill Area E: Evaluating evidence

I believe the method used was a very good way of investigating this topic.  It was done with precision, accuracy and the results produced were reliable. The investigation was not rushed to make any of the results outstandingly uneven.

As I was very careful, there were no anomalous results. This was good because it gives more precise

The results are good enough to draw a firm conclusion, as an accurate graph was produced from them.  

To extend this investigation I could observe the effect of resistance on different types of wires, such as their shapes and materials, and also to observe any other behavior such as energy loss through heat.    

If given further time I would investigate whether the pattern in my results is true beyond the range of values already used in this investigation.  To test the theory I would perform the test on an increased range of lengths to see what further affect it would have on the resistance.  Other aspects that could be investigated are the various variables mentioned in the planning.  

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