What Factors Affect the Current Flowing Through a Wire?

I am going to investigate how the resistance of the wire affects a current flowing through a wire. I know that as resistance changes, current changes, as Ohm's law:

I = V/R. If one part of an equation changes, the equal must be done to the opposite side. To detect how resistance affects current, I must first discover what factors affect resistance. These factors are:

* Length of the wire - if a wire is longer; there are more particles for electrons to move through, and therefore more resistance.

* Conductivity - depending on the metal of which the wire is made there will be less/more resistance.

* Temperature - many metals' resistance changes as temperature increases, that is why we use constantan wires.

* Diameter/Cross sectional area - if a wire has a larger diameter, then the particles have more room to flow.

I shall investigate what affect the diameter of a wire has on its resistance, and consequentially the current of the circuit. I shall keep the other variables constant, to ensure this is a fair test.

For this investigation, I will need the following apparatus:

* Power pack

* Variable resistor

* Ammeter

* Voltmeter

* 6 wires of different diameters

I will set up a circuit as in the diagram:

By running a constant voltage through the wire, I will be able discover the resistance of it with Ohms law, because of the constant voltage, and the fact I will know the resistance of the circuit using the variable resistor. I will maintain a constant, low voltage output from the power pack, so the voltage is not too high to be read by the voltmeter. I will connect the first wire, then run the pre determined voltage through it, waiting a short time until the ammeter has rested upon one result, and then record that result. I shall take 7 readings, each following the same procedure as the first, each of which will be of a different wire diameter. I will be using the following 7 wire sizes:

To ensure that these are in fact the correct diameters, as part of my pre-test, I shall use a micrometer to accurately read their diameters in 3 different places, and therefore work out an average thickness. If time permits I will perform more tests on each wire, so I can work out an average, and possibly discount anomalous results. To ensure the reliability and accuracy of the results, I shall keep the other variables at constant levels. I will also only change the diameter in controlled amounts. My graph shall also enable me to ensure the reliability of my results, as a graph shows all anomalies, which can be disregarded from my results. Also, to ensure the fairness of this test, I shall endeavour to make the wire a smooth as possible, as it will be fairly kinky, having been connected to a ruler for several years. This will make sure my wire is as close to 1metre long as possible.

To make this test safe I shall:

* Not run a large voltage, or any voltage regarded as unsafe through my circuit.

* Ensure power to the circuit is off before attempting to connect the next wire to be tested.

* Wear safety goggles to ensure protruding pieces of wire do not connect sharply with anyone's eye.

I have performed a pre-test to familiarise myself with the equipment, and also to test various