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How does the length of a piece of wire affect its resistance?

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Introduction

GCSE Double Science Coursework: Physical Processes Strand

1: How does the length of a piece of wire affect its resistance? By Matthew Colley TQN Science

Planning

Aim: For this piece of coursework, I will be investigating the effect of resistance on different lengths of wires, using Ohm’s Law. The wires we will be comparing are copper, Constantine 28 and Constantine 30. This experiment will be performed according to Health and Safety conditions under the guidance of the teachers.

Scientific Knowledge: -

A wire is a bundle of metal strips coated in plastic. The plastic can vary in colour and connect to different terminals

These are: -

? Black = negative terminal

? Red = positive terminal

? Blue = neutral terminal

? Green and yellow = earth terminal

? Brown = live terminal

The material varies because it has free electrons, which are able to flow through the wire. The number of the electrons depends on the amount of electrons in the outer energy shell of the atoms, so if there are more or larger atoms then there must be more electrons available. If the material has a high number of atoms there will be a high number of electrons causing a lower resistance because of the increase in the number of electrons. Also if the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase. Resistance is measured in Ohm's (Ω).

Resistance is caused by collisions - more collisions means more resistance.

...read more.

Middle

Whilst doing the investigation, it is important to keep safety into consideration. The scissors should only be used for cutting the wire to the appropriate length and for no other reason. Before using the power pack, the pointer should point at 0 volts. It is important to be careful while using the power supply. While handling live wires, it is essential to be careful. The voltage should be kept low because of the safety factor and the wires heating up.

Reliability

To make the experiment reliable, all apparatus must be checked to see if it is functioning properly and is giving a true reading. This will partly avoid systematic error. Another way to make the experiment reliable is to use two methods: to do the investigation in two different ways to measure the resistance when the diameters are changed. If one method contains systematic error or is very inaccurate, the other method will be used to recognise that.

Precision

I will take as many different results as possible so that there a wide range of results and that I am able to arrive at a good conclusion. To increase the accuracy of the experiment I will do repeats for all the experiments so when the mean is taken, an accurate table is drawn up and if one result is anonymous the other two results would contrast the anonymous result.

Fair Test

The investigation is to investigate the resistance when the diameter has changed.

...read more.

Conclusion

ody>

Length of Wire Readings

Metal: Copper

Resistance

Metal: Constantine 28

Resistance

Voltage: 10CM

0.23

0.62

(V)

0.21

0.76

Current 10 CM

1.82

1.66

(Amps)

1.81

1.60

Voltage 90 CM

0.63

0.63

(V)

0.61

0.6

Current 90CM

1.87

1.74

(Amps)

1.81

1.60

Length of Wire Readings

Metal: Constantine 30

Resistance

Voltage: 10CM

1.20

(V)

1.10

Current 10 CM

1.70

(Amps)

1.64

Voltage 90 CM

5.93

(V)

5.94

Current 90CM

1.00

(Amps)

1.08

Conclusion from Preliminary Experiment

 Copper will not be used because the results are very random and because copper has a low resistance. This means copper is liable to be inaccurate and very imprecise. The smaller the resistance the larger the percentage error which can occur and since copper has a very low resistance, it will have a very large percentage error making the results inaccurate. The other two materials show a greater consistency and show there are patterns and trends. They also have high resistances, which not only are easier to work with but also have a small percentage error and it is easy to observe changes. This is because the other metals have a high resistance. Other metals could not be used because it is not widely available. I will continue to use a 100 cm wire, as it gives me more reliable results than other lengths of wire – it has higher resistances and so it is easier to calculate the effect upon it, and using any other length wire would mean it would be harder to use effectively. We will continue to use the same method, as it did work quite effectively, although the wire we are going to use is the Constantine 28 as it has more resistance differences which means it will be easier to calculate during the real experiment.

...read more.

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