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Investigating how the length of a wire affects the resistance.

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The aim of my investigation is to find the relationship between the resistances of a wire at different lengths. An electric current in a wire is a flow of electrons and can be measured in amperes. Resistance is the natural property of all conductors to hinder an electric current.


In this investigation I will set up a simple circuit to read the voltage and current when the length of the wire changes. The length will range from 10cm - 60cm with intervals of 10cm. Moving the crocodile clip across the wire on a ruler will change the length of the wire. For each of these lengths I will find the potential difference across the wire length and the current flowing through it. I also decided that the best thickness of wire to use would be 30swg.This is because a thicker wire would cause too much heat, and the resistance of a thinner wire would be high and difficult to measure. The reason for this is that a thicker wire has less resistance, because there is more room for the electrons to travel through it.

The readings from the ammeter and voltmeter will be used to work out the resistance. This can be done using the formula: R = V/I (Ohm’s Law)                                                                                                                                                               V=voltage (Volts) I=current (Amps) R=resistance (Ohms)

Variables                                                                                  For this investigation I am going to have dependent and independent variables.

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The circuit should be set up as in the circuit diagram. It is important that the voltmeter is set up in parallel and the ammeter in series.





Preliminary work                                                                       I did a preliminary test as a trial of my investigation for the following reasons; to get an idea of the results and the range of value I would be working in, to get used to the equipment, to ensure that the wire did not get too hot, and to test the amount of cells to used in the circuit. The amount of voltage I used was important, as it would determine how hot the wire got. If the wire got too hot, energy would be given off as heat, and the resistance would have increased. I did a test that used the same piece of wire at different lengths with 1 and 2 cells. The results showed that with 2 cells, the resistance was higher due to the wire being hotter. For this reason I will use 1 cell to keep it a fair test. I needed to repeat the result for accuracy and reliability.

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Through out my investigation I found that I had anomalous results so I redid the test of 60cm, as the average resistance was 20.1 I found this result was too high to be reliable. This anomalous result could have been caused because of the wire heating up. I had a considerable amount of anomalous results, which lead me to feel that my results weren’t sufficient enough. Even though my results weren’t perfect, in that they don’t follow a set pattern, they do give me the information I need to prove my prediction. If I had to do the practical again I would improve it by keeping the current switched off for longer to ensure that the wire stays at the same temperature and repeating the readings more often. I would have also taped the ruler to ensure that it stayed in the same place and didn’t move. I also found that I could have used a copper wire instead of a Nichrome wire. However, Nichrome wire has more resistance but I would’ve had to do a further investigation to prove this. For further work I could have done an experiment to prove that Nichrome wire has more resistance than a copper wire.

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