Fair Testing
To make sure that my experiment is a fair test, I need to know the factors that could alter the accuracy of my results. 4 factors that affect resistance are:
- What metal the wire is made of.
- The thickness of the wire.
- The temperature of the wire.
- The length of the wire.
Therefore, I will need to use the same type and length (1 meter) of wire, at the same temperature each time. The only factor I will alter is the thickness. I will also make sure that my apparatus is self-supporting so that I cannot alter the experiment accidentally. I will repeat each experiment 3 times and then average my results to make sure that my results are reliable and fair.
Safety
To increase the safety of my experiment I will use covered wires (to protect myself from an electric shock) and make sure my apparatus is self-supporting (also to decrease the risk of an electric shock). I will not touch the wire whilst the power pack is on, as it will become very hot during the experiment. The exposed wire must not touch any surface at any point during the experiment or whilst it cools down afterwards. I will make sure this happens by using stands to keep the wire above ground level.
Range
- Wire – 0.18mm to 1.6mm, 1 meter long
- Voltage – 3V to 12V
- Repeat each test 3 times
- Voltmeter set to 20
- Ammeter set to 20
Analysis
The first graph, ‘A Graph to Show the Difference in Current and Voltage in Different Thickness’ of Wire’ shows that the thicker the wire, the bigger the resistance. This was first discovered by G.S.Ohm, who created the law, I = V/R. This law is the basis of my first graph. It also proves that my prediction is correct, because the electrons do give energy to the surrounding atoms, so that as the voltage increases, so does the resistance. My second graph, ‘A Graph to Show how Area Affects Resistance’ shows that the larger the area of a piece of wire, the less the resistance in the piece of wire. To find the area of the wire I used the equation: r2 and I averaged my resistance for each piece of wire to create one single line. This line shows a rapid decrease in R in section A, and a slower decrease in section B. I predict that if I were to extend my experiment the resistance would ‘level out’ to a lowest resistance, but wouldn’t get any lower than that point. This is because any piece of wire must have resistance in it. The third graph I have drawn involves the reciprocal of the area and the resistivity. It is based on the equation R = pl/A, which was adapted to my needs as R = 1/A (as I used the same length and type of wire for each experiment).
Evaluation
As I did my experiment 3 times I expect that my results were fairly accurate and reliable. To increase the accuracy of my experiment I also used the same length of wire each time, the voltmeter and ammeter at the same setting each time, and made sure that the wire was connected to the circuit in the same place during each experiment. The hardest part of the experiment is the calculation of results and the drawing of graphs, however I do not appear to have anomalous results. To improve my investigation I would try my circuit at a larger variety of voltages, as there are many gaps in my data and a clearer picture of the actual resistance needs to be achieved before I can make a more accurate analysis. I would also increase the number of thickness’ of wire to use, as this would also increase the accuracy of my analysis. To extend my investigation further I would use several other different types of wire to see if resistivity was affected by the conductivity of the wire.