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To investigate how the electrical resistance of a wire changes in relationship to it's length.

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Dave Attwood

Physics Investigation Of Resistance


Aim: To investigate how the electrical resistance of a wire changes in relationship to it's length.

The experiment will be carried out using  a current flowing through different lengths of wire, to see what effects are made in relation to the resistance.

Introduction: I am going to carry out an experiment with a wire, to test the resistance of it. I am going to do this in order to get a wider knowledge of how electricity works. Also I wish to learn more about the resistance of wires in relation to their lengths. As the electricity flows through the wire, it encounters obstacles in the molecules that make up the wire. Every time the electricity encounters a new obstacle, the resistance increases slightly. I will use a wide range of lengths in order to get the greater variation in results. I will repeat the experiments several times in the name of a fair test.

Prediction: I presume that as the length of the pieces of wire are change, the resistance will increase or decrease to the same pattern. this leads me on to presume that the rate of increase / decrease of the wire length, will directly lead to a proportionally accurate change in the resistance.

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As a result of the structure of all conductive atoms, the outer electrons are able to move about freely even in a solid. When there is a potential difference across a conductive material all of the free electrons arrange themselves in lines moving in the same direction. This forms an electrical current. When charged particles (current) encounter fixed particles (metal) they cause a collision. these collisions are known as resistance. When the resistance of a current is increased, this must require the force behind the current to increase. This makes resistance (ohms) is the same as the potential difference (volts) divided by the current (amps). this is called Ohms law.

                                        R=V / I

As the length of the wire increases, it stands to reason that the resistance increases because there are more particles to collide with and therefore the value for the resistance of the wire becomes higher. Resistance, in ohms (R) is also equal to the resistance of the wire, in ohm-meters (N) multiplied by the length, in meters (l) divided by the cross sectional area, in square meters (A).

                                        R=(N *I) / A

The material and cross sectional area of the wire is constant throughout the experiment. Therefore it is clear from the formula that the resistance should be directly proportional to the length.

Key factors:

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Most errors in our experiment were encountered in the measuring of the wire. This is because it simply was not very practical to hold a piece of wire straight, whilst holding it next to a ruler and then trying to accurately fix crocodile clips to the right part on the wire. Also I do not feel that the crocodile clips were always fixed securely to the wire with a good connection. This also meant that they were easy to move about on the wire changing the length of it. Errors rarely occurred in the setting of the current and the reading of the voltage. It was just in the preparation area that they did occur. Another example of this is the wire was never totally straight when we started the experiment, which may also, as said earlier on, effect the resistance of it.

I do not think that doing any more results in our experiment would have made it any more accurate. I feel that the only way to make it more accurate would be to use a different method – perhaps if we had a bar that did not bend, in place of the wire. We would then solder wires in the places that we thought would be most accurate so that there would be no chance of a faulty connection.

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