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Investigating the factors effecting resistance of a wire

Extracts from this document...

Introduction

Investigating the factors effecting resistance of a wire

Introduction

I am going to investigate the factors effecting the resistance of a wire.

This happens because of the electrons that flow through the wire. These electrons travel at a steady pace, when they come to a different piece of wire, they have to slow down in order to be able to pass. (This is why the current differs). While moving through the wire, the electrons need to squeeze together. This is because there is not enough room

Ohm's law states that the current flowing through the circuit is directly proportional to the voltage applied. (If you double one, you double the other.)

Electricity is conducted through a conductor, in this case wire, by means of free electrons. The number of free electrons depends on the material and more free electrons means a better conductor, i.e. it has less resistance. For example, gold has more free electrons than iron and, as a result, it is a better conductor. The free electrons are given energy and as a result move and collide with neighbouring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss as heat. It involves collisions between the free electrons and the fixed particles of the metal, other free electrons and impurities. These collisions convert some of the energy that the free electrons are carrying into heat.

Metals conduct electricity because the atoms in them do not hold on to their electrons very well, and so creating free electrons, carrying a negative charge to jump along the line of atoms in a wire. Resistance is caused when these electrons flowing towards the positive terminal have to ‘jumps’ atoms.

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Middle

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Fair Test

required lengths, because the cuttings might not be accurate and affect the results. Instead, I would use one 1 metre wire, and use a crocodile to slide on the wire to change the lengths of the wire that is connected to the circuit.

· Use the same wire throughout the experiment, to keep SWG exactly the same.

· Use an ammeter and a voltmeter to measure the figures accurately and to 2 decimal places.

· I would do the experiment in the same environment every time, so the temperature would be the same, so the resistance of the wire is not changed.

· Use different voltages (2V, 4V, 6V and 8V) as repeats to avoid anomalous results.

The factors, which must stay constant to keep the experiment a fair test, are:

· The power supply must stay on 2V

· The wire must be the same thickness

· The surrounding temperature must be constant

· The equipment should be kept the same

To keep this experiment as accurate as possible we need to make sure, firstly, that the length of the wire is measured precisely from the inside edge of the crocodile clips, making sure that the wire is straight when we do this. We must also make sure that the wire is straight when we conduct the experiment. If it is not, short circuits may occur and bends and kinks in the wire may affect the resistance. The reading that we take of the voltage should be done fairly promptly after the circuit is connected. This is because as soon as a current is put through the wire it will get hotter and we want to test it when heat is affecting it the least, i.e. at the beginning.

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Conclusion

Evaluation section. The reason why this is the likely explanation is because resistance is known to be inversely proportional to the cross-sectional area, i.e. if you increase the cross-sectional area (by increasing the diameter) then you decrease the resistance. This is because a wider wire means less likelihood of the free electrons having collisions and losing energy.

It is important to realise, however, that despite the fact that it would appear that the resistance of wire 2 is double that of wire 1, that does not mean that the diameter is half that of the wire 1. That is because if you halve the diameter then you decrease the area by a factor of about 3 (A = πr2)

The graph of experiment 1 is a straight line through the origin, which means R is directly proportional to L. This means that if the length is 40cm, and resistance is 2?, then if length is doubled to 80cm, resistance also doubles to 4.

This is because of the scientific idea, stated in the planning that if you double length, you double the number of atoms in it, so doubling the number of electron ‘jumps’, which causes resistance: The results support my predictions well, the results turned out the way I had expected, they match the predicted line well. I had predicted a straight line through the origin, which means R is directly proportional to L.

The graph of experiment 2 is an inversely proportional curve. This is because R is directly proportional 1/A, this means when A doubles, R halves. for example when the Area is 0.025mm2 the resistance is 4.8. When A doubles to 0.05, R halves to 2.4?. When A doubles again, R halves again to 1.2. This is because, as stated earlier: We see that if the area of the wire doubles, so does the number of possible routes for the current to flow down, therefore the energy is twice as spread out, so resistance might halve, i.e. Resistance is directly proportional 1/Area.

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