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Measuring the Resistance of a Wire - Investigation

Extracts from this document...

Introduction

MARK GRAHAM

GCSE SCIENCE

7/1/02                                                           Measuring the Resistance of a Wire – Coursework

PLANNING

Our aim is to investigate how length affects the resistance of a piece of 24 s.w.g (standard wire gauge) Constantan resistance wire. We will do this by measuring the resistance of the wire while seven different lengths, ranging from 40cm to 100cm, of it are connected to a circuit. This is a good range because the points are nicely spaced out down the length of wire, making it easier to identify the point at which the resistance starts to change. We will take seven readings so we can see if there is a pattern emerging in the results both in the results table and the graph.

Resistance wire –Resistance wire has a much higher resistance than copper wire; it is used to make resistors and heating elements for electric fires. They are made of alloys, i.e. mixtures of metals chosen to give high resistance, and are available in different thicknesses. Constantan and Nichrome are typical examples of resistance wire.

Background Knowledge

Resistance is measured indirectly. It is calculated by dividing the Voltage by the Current. Ohm’s law – V = I x Ω. To carry out this investigation accurately, we have to consider the factors, other than length, which affect the resistance of a wire. These factors areheat, length and thickness.

Heat –Resistance is caused by the atoms of a conductor interfering with the flow of the electric charges. As electrons flow through the wire they can collide with atoms, causing friction and heat.

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Middle

60

0.54

0.43

1.26

50

0.52

0.49

1.06

40

0.49

0.55

0.82

2.14Anomalous reading

Exp. 2 Point/cm

Exp.2 Voltage/V

Exp. 2 Current/A

Exp. 2 Resistance/Ω

100

0.60

0.29

2.07

90

0.59

0.30

1.97

80

0.57

0.34

1.68

70

0.56

0.37

1.51

60

0.54

0.41

1.32

50

0.53

0.47

1.13

40

0.50

0.58

0.84

Exp. 3 Point/cm

Exp. 3 Voltage/V

Exp. 3 Current/A

Exp. 3 Resistance/Ω

100

0.60

0.29

2.07

90

0.59

0.30

1.90

80

0.61

0.28

2.17

70

0.56

0.38

2.00

60

0.55

0.42

1.31

50

0.52

0.49

1.06

40

0.50

0.56

0.89

2.17 Anomalous reading

Exp. 4 Point/cm

Exp.

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Conclusion

Improvements/Further Investigation

To make the experiment more accurate we could keep the current constant and low to ensure the wire’s temperature also remains constant, therefore lowering the chance of a rise in temperature that might give the wire’s atoms more energy to interfere with the passing electrons. This improved experiment would give better, more precise results, and possibly, depending on what the cause of our anomalous results was, give a straight line on the graph of results.

If I had more time I could conduct more experiments to find out more about the resistance of a wire. I could investigate the effect of temperature by heating the wire. If so, I predict that this will result in a higher resistance due to the heat giving the wire’s atoms more energy to interfere with the passing electrons. I could experiment how the cold affects the resistance, too, but it would be complicated to keep the wire at a constant temperature for a fair test in both experiments. Another experiment I could conduct to find out more is the effect of changing the material from which the wire is made. I already know that better conductors have a lower resistance than poor conductors, so if I did this I would expect a higher resistance with the less good conductors of electricity. This would be a relatively simple experiment to conduct. I would simply have to measure the resistance of each conductor and determine how by altering the material of the wire I have changed it.    

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