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An investigation into the effect of changing the length of a wire on the resistance of that wire.

Extracts from this document...

Introduction

Phil Scott 10-5                July 15th, 2003

Physics – Mr Faulkes

An investigation into the effect of changing the length of a wire on the resistance of that wire

Aim:

In this investigation, we are trying to find out how the resistance of a wire is affected by changing the length of that wire. We are going to set up a circuit with an ammeter and a voltmeter in and then take the readings from them. With these readings, we can use the voltage, current and resistance equation to calculate the resistance of the wire. With the resistance results, we will be able to detect any trends and make a valid conclusion as to how the resistance is affected by the length of the wire.

Prediction:

I predict that as the length of wire is increased, the resistance will also be increased. I think this is because in a longer piece of wire, the current will have further to travel and so there is more wire to create resistance. In a shorter wire there would be less resistance because there isn’t as much wire to create the resistance. Therefore, I think that the 10cm of wire will have the least resistance and the resistance will gradually increase up to 50cm of wire having the greatest resistance.

Scientific Background:

        Resistance is the property of any object or substance of resisting or opposing the flow of an electrical current. The quantity of resistance in an electric circuit determines the amount of current flowing in the circuit for any given voltage applied to the circuit. The unit of resistance is the ohm, which is the amount of resistance that limits the passage of current to one ampere when a voltage of one volt is applied to it.

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Middle

25

4.16

0.99

0.24

34

25

4.15

0.90

0.22

Average Readings

4.16

0.92

0.22

Wire

SWG

Length (cm)

Current (A)

Voltage (V)

Resistance (Ω)

Nickel Chrome

36

25

0.27

2.31

8.56

36

25

0.26

2.30

8.85

36

25

0.26

2.28

8.77

Average Readings

0.26

2.30

8.72

Wire

SWG

Length (cm)

Current (A)

Voltage (V)

Resistance (Ω)

Constantan

24

25

2.60

1.39

0.53

24

25

2.60

1.40

0.54

24

25

2.62

1.42

0.54

Average Readings

2.61

1.40

0.54

I then used these results to help me select an appropriate wire to use for the real experiment. As you can see from the results, nickel chrome and constantan (SWG of 36) had the highest resistance. Usually, I would have used one of these wires in the final experiment because they both have high resistance and so they would both be good for my experiment. However, while conducting my pretests, I noticed that when I used nickel chrome and constantan (SWG of 36), both of the wires got very hot and I had to let them cool before I could remove them from the crocodile clips without burning myself.  

The reason I chose to use constantan (SWG of 24) was that it was the wire that had the most resistance, but wouldn’t get hot. I couldn’t use the other wires because they got too hot to touch and if they didn’t burn me or the bench I was working on, they would certainly have slowed down my experiment by making me wait for them to cool before I could repeat the experiment.

        Apart from the adjustment to my aim, the way in which I conducted the pretest and the real experiment and the way that I set up the equipment were identical.

Results:

        These are the results that I obtained from the real experiment. I have entered the results from the three repeats that I did.

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Conclusion

        I feel that my results are very reliable and that they are sufficient enough to support the conclusions that I made from them about the trends of the current, voltage and resistance. Because my results are sufficient enough to support my conclusion, they also prove my prediction to be correct.

Further Experiments:

        If I were to do further research into the resistance of wires and how the length of the wire affects the resistance then I would probably test different wires. In this experiment, I only tested the 0.5588mm constantan wire. This gives me enough data to draw conclusions about this wire, but I cannot make any conclusion about the resistance of other wires compared to their length. If I wanted to find out more about the resistance in wires then I would test the other wires that I used in my pretest like nickel chrome and copper. I would conduct the experiment in exactly the same way and use the same lengths of wire. The reason I would do this is so that I could compare the results that I got from these wires with the results that I already have from the constantan wire. With these results I could then draw conclusions not just about the resistance compared to length, but also about the resistance compared to the diameter of the wire. On the graphs that I produced, I would plot diameter of wire along the x-axis and the resistance along the y-axis and then just plot the resistance’s of wires of the same length. I would draw five graphs, one for each of the wire lengths, and then compare them all with each other to be able to draw conclusions about more than the length against the resistance.

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