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# To investigate the factors which effect the resistance of a wire.

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Introduction

Title:   The Resistance in a wire.

Aim:To investigate the factors which effect the resistance of a wire.

Background and Predictions:

There are something important we should know, which can effect the predictions and that is Resistivity. Resistivity is the resistance in each metre of a wire and resistivity is measured in ohms per metre, and the law of resistivity is: -

Resistivity = resistance X cross section area

Length

= R X A = Ω/m

L

As known by Scientifics, resistivity is always constant and for the resistivity to be constant all the time, by the law above one of the factors on the right side of the law must be directly proportional to the resistivty and that is resistance. So if a material has high resistance then it has high resistivity.

Different materials have different resistivities:

Copper = 1.69 X 10

Nichrome (Ni, Cu, Al)= 1.30 X 10

Constantan = 4.8 X 10

And by the way, the less the resistivity the material has, the better conductor it is.

My predictions for the experiments I’m going to do are: -

1. The longer the wire, the greater the resistance it has.

Middle

0.18 Ω

0.175 Ω

15cm

0.18v

0.20v

1A

1A

0.18 Ω

0.20 Ω

0.190 Ω

20cm

0.27v

0.19v

1A

1A

0.27 Ω

0.19 Ω

0.230 Ω

25cm

0.30v

0.26v

1A

1A

0.30 Ω

0.26 Ω

0.280 Ω

30cm

0.35v

0.33v

1A

1A

0.35 Ω

0.33 Ω

0.340 Ω

Copper, 20swg

 Length Voltage /V Current /I Resistance /R AverageResistance 1st 2nd 1st 2nd 1st 2nd 10cm 0.10v 0.10v 1A 1A 0.10Ω 0.10Ω 0.100 Ω 15cm 0.16v 0.15v 1A 1A 0.16Ω 0.15Ω 0.155 Ω 20cm 0.14v 0.14v 1A 1A 0.14Ω 0.14Ω 0.140 Ω 25cm 0.15v 0.12v 1A 1A 0.15Ω 0.12Ω 0.135 Ω 30cm 0.13v 0.11v 1A 1A 0.13Ω 0.11Ω 0.120 Ω

Nichrome, 15cm

 Thickness Voltage /V Current /I Resistance /R AverageResistance 1st 2nd 1st 2nd 1st 2nd 32swg 3.40v 4.10v 1A 1A 3.40Ω 4.10Ω 3.750 Ω 26swg 1.40v 1.40v 1A 1A 1.40Ω 1.40Ω 1.400 Ω 20swg 0.40v 0.45v 1A 1A 0.40Ω 0.45Ω 0.425 Ω

Constantan, 15cm

 Thickness Voltage /V Current /I Resistance /R AverageResistance 1st 2nd 1st 2nd 1st 2nd 32swg 1.3v 1.3v 1A 1A 1.3 Ω 1.3 Ω 1.30 Ω 26swg 0.9v 0.

Conclusion

There were some thing, which effected the results of the experiments, and one of them is the crocodile clips and we noticed that putting the wire on the edge of the clip gives a different result than putting it far inside the clip. Also we had to clip the wire right exactly on the edge to give proper result. Because of doing the experiment all along 6 days and we didn’t use the same exact equipment each day then this may effect the results. Once, we measured the thickness of one of the wires and we found that it has different thickness than it says on the label and that effects the results, of course. One of the important things, which can effect the results of resistance and that, is Heat. When we used a bulb in the circuit, the filament in the bulb gets hotter and when it gats hotter, the atoms of electricity get collision and move faster and this happens can effect the resistance, therefore the results at beginning of the experiment differ the results at the last of the experiment.

I suggest that to extend the enquiry of the experiment, we shall use much longer wires e.g. 2m, 3m… and by that we can have better sight on resistivity.

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