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# To see how the length of a wire affects its resistance. To find the wire to test, I'm going to test 4 different types of wire in another experiment

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Introduction

`Resistance of a wire –Electricity Coursework

Aim:

To see how the length of a wire affects its resistance.

To find the wire to test, I’m going to test 4 different types of wire in another experiment and use the one with the highest resistance.

The Theory behind the Experiment

Theoretically the length of a wire should affect its resistance.

Electricity encounters a certain amount of obstruction when passing through a wire depending on its length, width, temperature and type of metal, this obstruction is called the resistance and is measured in ohms.

The longer and thinner the wire the harder it is for the electrons to flow through, because there are less spaces for it to flow through and more obstructions along the length. It has a similar principal to the flow of water and how it is impeded when passing through a long and narrow pipe. Therefore the longer the wire is the more resistance there should be.

The other factor that can affect the resistance is the metal type, for example the resistance of an Iron wire is about seven times greater than that of a copper wire with the same dimensions, and this is because of the varied amount of ions in the different metal, more ions in Iron mean that electrons find it harder to pass through. This is the reason why copper is used in electrical wire; because it gives little resistance less energy is used to make it flow. I need to test 4 different wires in the first experiment; to find the type of wire with most resistance. It is important that for both experiments I let the wire cool down for a few seconds after taking the reading, as temperature can affect the resistance.

Middle

0.18

3.3

0.176

3.3

Manganin

0.91

1.50

0.88

1.59

0.88

1.62

0.89

1.62

Nichrome

1.18

0.8

1.19

0.84

1.18

0.84

1.183

0.84

Constantan

0.93

1.46

0.93

1.46

0.96

1.53

0.94

1.53

There is hardly any variation in the results for each test.

This is a chart to show the most resistant wire:

 Metal Workings Resistance (ohms) Copper 0.176/3.3 0.05 Ω Manganin 0.89/1.62 0.57 Ω Constantan 0.94/1.53 0.63 Ω Nichrome 1.183/0.84 1.43 Ω

1ST Experiment

Results

We can clearly see which metals have the highest resistance and which have the lowest, in order from highest to lowest they are: Nichrome, Constantan, Manganin and Copper, because it has such a low resistance copper makes a great wire for electricity to pass through to components around the house because a low voltage can provide such a large current.

The electrons are freed from the battey that is slowly deteriorating letting more and more electrons free, they move from negative to positive – the opposite direction to conventional current (the direction people thought electricity would flow).

The highlighted metal, (constantan) is the metal I’m going to use in the second experiment. Ideally I would use Nichrome but there is a shortage of supplies so we couldn’t obtain a length of Nichrome wire so Constantan is the second best as it has the second highest resistance.

Method

The testing for this experiment was sound; no faults were recorded because we had 3 sets of results making the results very accurate when getting an average the results for each test were also very similar anyway.

Improvements

Although the averages were correct, I feel that in some parts of the tests we did not leave the wire to cool for long enough and so the resistance was amplified, next time I do the experiment I will leave the wire to cool for exactly 30 seconds and set a stop watch to records this. Another way of preventing the wire from overheating is by attaching a light bulb to the circuit to absorb the heat. I will also make sure that I record the results immediately otherwise the wire will again overheat and the results will be distorted.

The results for the second experiment are as follows:

 Length in cm Test 1 Test 2 Test 3 Amps Voltage Amps Voltage Amps Voltage 10 3.82 0.53 3.75 0.45 3.79 0.44 20 2.76 0.6 2.82 0.67 2.87 0.68 30 2.37 0.73 2.3 0.82 2.3 0.84 40 2.58 0.67 1.93 0.92 1.97 0.92 50 1.88 0.84 1.68 0.99 1.69 1.01 60 2.8 0.79 1.47 1.06 1.49 1.06 70 1.67 0.9 1.3 1.1 1.32 1.1 80 1.76 0.8 1.19 1.14 1.19 1.14 90 1.54 0.92 1.09 1.17 1.1 1.18 100 0.97 1.14 1.01 1.19 1.02 1.2

Conclusion

Improvements

If I was to do the experiment again I would check the circuit carefully before every test to make sure there are no faults, this would prevent anomalous results like the ones I had in my experiment.

I could extend my experiment by using different types of wire and see whether the same length and resistance rule applies for them, although the rule would probably not work as well for a wire with more resistance because a higher temperature increases the resistance itself and distorts the readings. If I had access to Nichrome I would use it to test the rule because it has a very high resistance and therefore would be unlikely to get inaccurate readings as a result of overheating. Testing different types of wire of higher resistance would give me more reliable information to support my rule; Ohms law.

Overheating causes the atoms to vibrate more in the wire making more of an obstruction for the electrons to flow through.

If I were to do the experiment again I might try putting 2 wires of the same type in parallel with each other record the resistance of both and see if the length of each wires correlates with the resistance of each wire in the same way as in a series. They should correlate because in the theory I explained how the current divides in a parallel so the resistance will probably be greater per cm of wire because resistance = voltage/ current and if the current is smaller resistance will be greater.

Even though the second graph proves my prediction with more accuracy, the first graph still shows some correlation to also prove my prediction. For in the first graph the results still show vaguely that resistance is proportional to length:  at 10 cm resistance 0.1ohms and at double the length (20cm) the resistance is also doubled (o.2 ohms). The only problem with the first graph is that a lot of the results do not show this trend.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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