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An Experiment to Find the Effect of Length of Wire on It's Resistance

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Introduction

An Experiment to Find the Effect of Length of Wire on It’s Resistance

Background Information

Resistance, Ohm’s law; the current through a metal wire is proportional to the difference across it (providing the temperature stays constant).  Current – the flow of electrons around a circuit, Voltage – the electrical pressure within that circuit. Using this information, I know that; to find the resistance of a wire we simply divide voltage by current         ( R = V  ).

                                   I                

Knowing this, I can find the resistance quickly, and come to a conclusion faster on the affect of length of wire on the resistance. Resistance is the amount electricity is slowed down whilst passing through a conductor. It is slowed down by the electrons repelled by the power supply, colliding with ions. Copper has a different ion arrangement and, a low resistance, this also renders copper useless for this experiment. The two options for wires in this experiment are, nichrome and constantan.

            For a flow of electrons there needs to be a circuit. A complete circuit needs electrical conductors, metals are good conductors because they have free electrons which can leave the atom and move around the circuit. When atoms lose or gain electrons they gain a charge, and are subsequently then called ions.

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Middle

1                                0.05                                20.00

40 cm CONSTANTAN

5                                1.43                                3.49

4                                 1.13                                3.53

3                                0.86                                3.48

2                                0.57                                3.50

1                                0.28                                3.57

40cm NICHROME

5                                0.64                                7.81

4                                0.51                                7.84

3                                0.38                                7.89

2                                0.27                                7.40

1                                0.13                                7.69

Analysis of preliminary

From the results of the preliminary experiment I can deduce that Constantan has the least varied results, and therefore the most reliable results, due to this I will use constantan rather than nichrome in my main experiment. According to ‘Science Data Book by R.M.Tennent’ constantan has a resistance of 8.29; we gained an average of 8.63, this was near, and so was another helpful point at which to base our nichrome/constantan decision on. We also saw the affects of leaving on the power supply whilst the results are being recorded, the wires did get very hot, very quickly, and so also needed changing for the main experiment.

Main experiment

Safety

Ensure that wires do not over heat.

Do not pull on the wires as they can cut through the skin.

Do not spill liquids on the equipment.

Plan

For the main experiment I will set up the apparatus in the same way to the preliminary (shown in diagram). I will use constantan for reasons previously explained. I will also, for a more accurate and reliable set of results, use five voltages for each length.

Set the required length, starting with the longest first so as to reduce the risk of over heating or burning out the wire and ruin the experiment.

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Conclusion

Evaluation

I am very pleased with the high level of accuracy of my results, especially for the 100cm length at which all resistances were the same. The points on my graph almost all lay on the line of best fit, which displays a high level of accuracy – which is helpful to draw a reliable conclusion, with no particularly anomalous results. For accuracy I used six different measurements, and didn’t have to repeat any of them. I took into account needing to allow the wire to cool, by turning off the power whilst taking readings, and keeping the cross sectional area constant. We maintained this using a 32 s.w.g. each time. Another factor to take into consideration was the angle at which the crocodile clips intercepted the constantan wire; we maintained this as a 90 degree angle, as it is the easiest to repeat. To investigate further into this experiment I could use different wires materials at different lengths and see if similar patterns and rules apply. If I was repeating this experiment altering one factor I think I would have used a wider range of wire lengths, to get a more accurate and detailed conclusion. I would also ensure that the crocodile clips have been connected to the wire at 90 degree angles each time, I think this was done, but it wasn’t something we regularly checked.

                                                    -Stefan Nagorski -

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