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Investigating the Resistance of a wire

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An Experiment to Test the Resistance of a Wire

What is resistance?

When an electric current is flowing round a conductor, free moving electrons flow in the spaces between atoms. As they do this, they eventually collide with the atoms in the wire. This is resistance. Resistance is measured in Ohms (Ω).

        Because Resistance = Voltage ÷ Current (Ohm’s Law), I will be able to work out the resistance of the wire by measuring the voltage and dividing it by the current running through the wire.

What can affect Resistance?

        There are several factors which can affect the resistance of a wire. Firstly, the thickness of the wire can affect the resistance. This is because in a thinner wire, the atoms are more closely packed together, this means that electrons collide with atoms more often because there aren’t as many spaces between atoms for the electrons to move.

        The length of the wire, the variable I will be changing throughout my experiment, affects resistance because in a longer piece of wire, there is a higher resistance. This is because in a longer wire, there are more atoms for electrons to collide with. This increases the resistance of the wire.

        Also, the type of wire I will use has an effect on the resistance.

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        This preliminary work is important to check whether or not my method works. It is important to get the method correct. Here are the results from my preliminary enquiry:

Length (cm)




































        The preliminary work showed that my method would work and provide accurate results that I could use to investigate resistance. I didn’t find any part of my preliminary work that I would change. For my experiment, I will use the same apparatus, set up in the same way as shown for my preliminary work.

To keep this experiment a fair test, I plan to keep the voltage the same for each length of wire. I can do this by setting a fixed voltage on the lab pack. I also plan to use the same thickness and type of wire for each length, as this stops different thickness’, which have different properties, from slightly altering the results, as I want the results to be as accurate as possible. I will also prevent the temperature from altering the results.

To carry out the experiment, I set up the equipment as shown. Then I started with a 100cm length

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        I think that the method I used worked well, as I got a fairly reasonable set of results, which seem to fit in with what I expected to find. There were, however, several anomalous results. On the first experiment, the resistance for the 30cm strip of wire was quite a bit lower than the average and the results from both the second and third experiments. This maybe due to a fault, e.g. in the lab pack, or it may be that I carried out this experiment wrong at first, but I don’t think I did because I got fairly accurate results from my preliminary work.

        I would, however, change one or two things if I had to repeat this experiment. Firstly, I would perhaps use a different range of values, to further investigate resistance. I would also change the voltage on the lab pack to see if this affects the resistance in anyway, or maybe I could change the type of wire, because other types of wire than Ni-chrome will have different properties, and the results I will get will be different. This might also change the conclusion I get from the results.

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