What factors affect the resistance of a wire

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John Saunders (10R) April '02

Assessment practical

Investigation: what factors affect the resistance of a wire?

Introduction:

In the experiment I will see if the resistance is affected by diameter of a wire.

In this case, it wouldn't matter how long the wire were to be, as long as a wire has a larger diameter, then it would have a larger volume in which the electrons flowing in it could use up. This extra space will create more space per electron to flow in, and so it is likely that fewer collisions will occur. Smaller number of collisions means that the resistance will be smaller, so the resistance should be affected because it will now be less.

The diagram above shows two wires of the same length, but with a different diameter. Whereas a longer wire has a larger area in which more collisions can occur (because the electrons have further to travel), a wider wire has more area in which less collisions can occur. This is because the wires are the same length, which means the electrons have the same distance to travel, but at the same time wider wires have more room per electron when flowing. This means there is less chance of two electrons colliding.

This can be demonstrated by people walking down a corridor, if there are a thousand people walking down a five meter wide corridor, it would be a lot harder and a lot slower than if the corridor were 50 metres wide, because there would be more room for people to get down it and less friction (heat energy) will be produced. Heat energy also causes resistance.

Method:

In the experiment, we will use:

* An ammeter and voltmeter

* A lab pack (for mains supply)

* Different diameter wires (that are 0.16, 0.25, 0.31, 0.45, 0.71 and 1.25mm wide), all being one metre long.

* Link wires (to complete the circuit)

* A one-metre ruler

In this circuit, which we will use for the experiment, the cell represents the lab pack battery, the circled V and A represent the voltage reader and current reader respectively, and the dotted line represents the one metre wire we shall use with the different diameters.

In the experiment, I will use one metre of wire, which will be measured using a board set up by the science dept. so that the wires are perfectly straight and parallel to each other, and so that it cuts out all the nonsense of measuring wires which are not fixed in place anywhere. The main advantage of this isn't only that it will save a lot of time, but if the wires are coiled in the experiment, the resistance could have been affected more than we wanted (like with the filament in light bulbs).

I will also need to do several tests with the experiment, to make sure that any inaccurate results don't affect my final results too much. As I will explain in more detail in my fair test section, if I was to only do one test, then any anomalous results will look a lot more inaccurate than if I was to do two tests, in which I could look for flaws in my method that could have been making my tests inaccurate. This could make my second test a lot better, and therefore make my average result a lot more accurate.
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I will set the lab pack voltage to 2V. I will measure the voltage of the circuit in volts and I will measure the amp level of the circuit in amps. I will then use these measurements of the voltage and current to find the resistance of the wire, in ohms (?)

I will use the formula R = V ? I, meaning resistance (?) = voltage (volts) ? current (amps) to work out the resistance of the wire.

Fair test:

I am going to make this experiment a fair test by doing several things. ...

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