What Factors Affect the Current Flowing Through a Wire?
Essay Preview: What Factors Affect the Current Flowing Through a Wire?
Report this essay
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 Ohms 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 anyones eye.
I have performed a pre-test to familiarise myself with the equipment, and also to test various