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# Investigate the factors which affect the resistance of a wire

Extracts from this document...

Introduction

Tom Gowing 10A Physics Coursework

Coursework: Investigate the factors which affect the resistance of a wire

What is resistance? The dictionary defines resistance as: the property of any object or substance of resisting or opposing the flow of an electrical current. Put simply it is the ability of a material to restrain the amount of current going through it.

There are many factors that can affect the resistance of a piece of wire. Length, thickness, material and temperature of the wire can all affect its resistance to current. For example as we found out in class work in year 8, 20cm of copper wire has far less resistance than a 20cm length of nickel wire, simply because copper is a better conductor. Resistivity is the measure of how much a substance can restrain electrical current. This will also be calculated using my final results, comparing this to the official resistivity of the wire will also tell me how accurate my results were.

I am going to investigate how the length of a piece of wire affects its resistance. For this experiment the wire we used was an alloy, rather than copper. This is

Middle

2V

1.10A

1.13A

1.13A

1.12A

3V

1.55A

1.62A

1.56A

1.57A

4V

2.40A

2.25A

2.21A

2.28A

5V

2.60A

2.75A

2.69A

2.68A

6V

3.18A

3.23A

3.34A

3.25A

The results all proved to be so close together that it proves it’s not worth doing it for every measurement.

Results
 1V 2V 3V 4V 5V 6V 20cm 1.12A 2.43A 3.63A 4.62A 6.37A - 30cm 0.44A 1.42A 2.32A 3.20A 4.10A 5.10A 40cm 0.65A 1.32A 1.95A 2.58A 3.33A 4.19A 50cm 0.53A 1.06A 1.60A 2.12A 2.68A 3.22A 60cm 0.44A 0.85A 1.29A 2.04A 2.65A 2.99A 70cm 0.37A 0.

Conclusion

The real test for how accurate my results were is to calculate the Resistivity of my results and to compare it with the Resistivity that the wire should be.

Resistivity is a property of a metal (whereas resistance is a property of a component). Resistivity does not depend on the dimensions of a component, only on the material from which it is made. We have done previous experiments to show that the resistance (R) of a conductor is directly proportional to its length (l) and is inversely proportional to its area (A). The diameter for the wire used was around 0.8mm.

To put this into a formula, where p is the Resistivity:

R = pl

A

So:

P (Resistivity) = AR

l

If we take the results for 80cm of wire we can work out the Resistivity of Constantan (the alloy wire we are using).

When l = 0.8m R = 2.7Ω

P = 0.000000173 x 2.7  = 6.07x10 –8  Ω/m

0.8

In an A-level textbook I looked up the Resistivity of Constantan and discovered it should be 4.9 x 10 –8 Ω/m

These two figures are fairly close and this indicates how accurate my experiments were.

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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