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# What Factors Affect the Resistance Of A Wire?

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Introduction

What Factors Affect the Resistance Of A Wire?

I am going to investigate one of the factors that affect the resistance of a length of wire.  I will use this circuit:

## Planning

I will set up the circuit as shown in the diagram above.  I will take 10 readings, of volts and current, across the full length of wire available starting at 0cm, to give me the circuit resistance, to give a full range of results.  I will repeat these readings 3 times in case any anomalous results should occur as a result of an inconsistent wire due to it being damaged.  I will then find the average resistances and plot them against length on a graph.  I will take lengths from 0cm, by clipping the crocodile clips together, to 54cm, measuring every 6cm.

I will make it a fair test by fixing the cross-sectional area of the wire and the materials it is made from.  The current will be kept as constant as possible.  Ideally, I would keep the temperature of the wire the same, too, but it can be tricky.  To try and sustain a constant temperature I will switch off the power supply after each reading to allow time for the wire to cool.  I will also use a small current, which will help to keep the temperature down.

Middle

I think that the results will produce a straight-line graph showing that resistance is proportional to length.  I think that the graph will have a non-zero intercept because, at 0cm, the resistance of the rest of the circuit will be measured.  The graph may be slightly curved due to an increase in temperature, which will cause a higher resistance than expected.

## Analysis

I have found that the resistance of the wire increases with length.

As I predicted, the graph shows linear variation showing that the resistance is proportional to the length.  The first few results, up to and including 24cm, produce a slight curve because the short lengths of wire got hot, causing more resistance than expected.  This is due to a greater energy transfer and a reduced current.  The graph is a straight-line graph.  A resistance is shown for 0cm of wire because the rest of the circuit gives out a resistance, which, in this case, is an average of 0.13Ohms.  The gradient of the graph, or resistance per metre, is 13.85 Ohms/m.

To create the graph, I found the average of the three resistances I obtained for each length in the experiments.

Conclusion

To obtain more results to see if the conclusion was correct, another length of nichrome wire could have this experiment repeated on it and it would be possible to see if the readings are similar.  Another way to obtain more results would be to change the material of the wire and test to see if its length had the same effect on the resistance of it.  The experiment could be repeated and the same number of readings of the same lengths could be taken.  A graph could be plotted and, although the gradient may be different, it would then be possible to see if the resistance was proportional to the length.

Overall, I think that the procedure used was successful and produced accurate results.

Charlie Durber        26/04/07        10BC1

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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