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Investigate the factors which affect the resistance of a wire.

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Physics Coursework-Resistance Investigation:


To investigate the factors which affect the resistance of a wire.

Key Equations:

To work out the resistance of a wire you use the formula:

R = V/I

Where R is the resistance, V is the voltage and I is the current flow.

Another way to work out the resistance of a piece of wire (possibly if you are investigating the cross section area of the wire) you use the formula:

R = p L/A

Where p is the resistivity of the wire, R is the resistance of the wire L is the length of the wire and A is the cross section area of the wire.

Introduction and background information:

The definition of resistance is prevention of an electric current by means of electron flow and ions. Current is measured in amps and is the flow of charge in an electrical circuit and this is moved round the circuit by voltage. Voltage is the same as potential difference and is measured in volts. Resistance is measured in Ohms and is the calculated difference between the ends of a conductor, divided by the current flowing through the conductor.

The relationship between both voltage and current is explained by Ohm’s Law:

The current through a device is directly proportional to the potential difference (voltage) across it if the temperature remains constant. Showing that if there is a greater resistance there will also be a greater voltage to push the same amount of charge through the wire.

If you have to put 1 Volt across something to pass 1 Amp through it, then it must have a resistance of 1 Ohm (Ω the Greek letter Omega is the symbol of resistance, The Ohm).

Electricity is passed through a metal by the movement of free electrons.

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The resistance of different materials determines how much energy is need to push the charge through the device. If there are lots of ions (vibrating with energy) in the way, the easiest route for the electrons to take between the ions is blocked. If no current is allowed through the material is then called an insulator.

From this I can predict if I change the material the wire is made from the resistance of the wire will also change.

The factor that I have chosen to investigate is; the length of the wire. I have chosen to investigate this because I feel it will give the best results and affect the resistance of the wire evenly as discovered by the preliminary results.

If I increase length of the wire the resistance of the wire will also increase.

If I decrease length of the wire the resistance of the wire will also decrease.

Fair test:

It is important to do a fair test because otherwise your results may vary or be inaccurate. A fair test is an experiment were you only change one area or measurement that you are going take e.g. the length of the wire. The other areas of the experiment should stay constant and not change.

The factor I have decided to investigate I think will produce the fairest and best results possible to me to back up my prediction.

When I do my experiment I will only change the length of the wire used. To keep it fair I will use the same: wire as the wires have slightly different cross section areas along them and made are from different materials we used a 36 standard wire gauge and we measured the average cross section area being 0.211mm ranging from 0.208 to 0.

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The predictions were supported by both the scientific knowledge and results and have been proven correct. Overall I feel the results created a definite trend and backed up my predictions. This conclusion will work for these results but possibly not for all. More results would need to be taken to prove the predictions always work.


I feel the experiment went reasonably well and the results backed up and agreed with the prediction and the conclusion. If I was to repeat the experiment I would take more results at smaller increments along the wire to reduce in-accuracy as the cross section area of the wire changes along its length. This would prove definitely the predictions were correct and that the results were the same when using different lengths of wire. I could also see if there is a constant change in resistance compared to length when there is a greater voltage supplied to the circuit for example 8V.

If I were to do experiment again I would take more results and also take more accurate readings. I could do this by using better equipment for example: measuring the temperature of the wire so that there was very little change in this. I could start the experiment each time with the wire being at a constant temperature to make the experiment more precise. We did not have enough equipment to do this in the laboratory and so had to rely on the fact that temperature wouldn’t change the results too greatly.

Overall I think the experiment was very successful and clearly proved my predictions. If you increase the length of a wire, the resistance also increases. The resistance of a wire is directly proportional to the length of the wire.

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