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An experiment to investigate the factors affecting the electrical resistance of a wire

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An experiment to investigate the factors affecting the electricalresistance of a wire

All wires in a circuit offer some resistance to the flow of charge. Wires with a low resistance allow electrons pass through easily, however, wires with a high resistance need more collision to move the electrons through them. By altering the resistance of a circuit, we are also changing the currents and voltages.


In this experiment, I am going to investigate how would the length affects the electrical resistance of a wire.

Plan and fair-testing

Circuit diagram of set up:image01.png



1. Voltmeter       2. Ammeter             3. Variable resistor

4. Battery                                              5. Wire  

6. Wires for connections of the circuit         7. Crocodile clip

By using the above circuit and the apparatus, I can then able to start my investigation. For this experiment, I am going to use 8 different lengths of wire and they will be from the range of 10 cm to 80 cm. This can provide me a more accurate and reliable results. First of all, I should start with a wire of 80 cm long as the wire, then hold it with a crocodile clip in order to stable it. An ammeter and a voltmeter is linked to the circuit and therefore, when current flow through the circuit, I will be able to read both the results on the ammeter and voltmeter.

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R α l. Now, I can say that the length of the wire is proportional to its resistance, and this means if the length of the wire increases, the resistance will increase as well.

The equation of R=V/I can help me to understand that the length of wire is directly proportional to the resistance. After I have obtained eight different resistances, I can then plot a graph of the length of wire against resistance to investigate the relation between these two variables. If a straight line is drawn from the origin of the graph, it proves the length of the wire is directly proportional to the resistance.

The equation of R=pl/A can also prove whether the length of the wire is proportional to the resistance as well. The units are:

R = resistance (Ω)

l = length of wire (cm)

A = Cross section area of the wire (cm2)

ρ = resistance of the material of the wire

In the equation, ρ is the constant of proportionality and will have the units of resistance x length. This constant, ρ, is called the resistivity of the material and from the equation we see that if l = 1 cm and A = 1 cm 2, ρ=R. Therefore, I would say if the length (l) and the area (A) is double, the resistance (R)

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   In general, I am quite delighted with my investigation, but I think some of the careless mistakes could be avoided in order to improve my results and make it more accurate. There was one anomalous result on the investigation of a 30cm long wire. On the 7th reading, the point on the graph has gone off the best-fit line. This might be possibly caused by the wire was bended when I was investigating. This small change of length might have an effect on the results. Also, the readings from the ammeter and voltmeter are always having of difference of ±0.1, and this might have a small effect on the results. In addition, the electricity supply might be weaker towards the end of the investigation, which may again bring tiny errors on the results. However, apart from that error, I am confident throughout the whole investigation as the points on the graphs are all fit in the pattern of best-fit and is a straight line through the origin.

   To improve the experiment, I have to ensure that the lengths of the wire are accurate, and not bended. Using a new piece of wire can do this; nevertheless, keeping the diameter constant is vital as well.

   The results that I have obtained are sufficiently reliable to support the conclusion as all the graphs that I have produced are best-fit and through the origin.

Charles Ng

Physic Coursework                06/07

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