The different lengths of wire I will be using will be: 10cm, 20cm, 30cm, 40cm, 50cm, 60cm, 70cm, 80cm, 90cm and 100cm.
Equipment
Metre ruler, constantan wire, power pack, ammeter, crocodile clips and wires, paper clips.
Fair Test
To make it a fair test I will be using the same wire (constantan) each time, of the same thickness, and I will be keeping the voltage the same throughout. This is to ensure that all other variables are kept the same that could affect the results I gain.
Safety
I will be performing the experiment away from any water source, and using a voltage that will not heat the wire enough to cause a burn.
Trial Run
I performed a trial run to determine how I could perform the experiment to gain suitable results. I used 1 volt for the trial run and used each of the lengths ranging from 10cm to 100cm.
From the trial run I realised that using 1 volt does not give good current readings as they are not spread out enough to be accurate. Therefore I will need to use a higher voltage and I feel that 2 volts will give more accurate readings.
Results
Using 2 volts spread out the current readings more and enabled me to see the pattern a lot more accurately. From the results you can see that the current increased as the length of the wire increased.
From these current readings I could calculate the resistance:
100cm = 21.5 Ω
90cm = 20.0 Ω
80cm = 17.1 Ω
70cm = 15.4 Ω
60cm = 13.3 Ω
50cm = 11.6 Ω
40cm = 9.4 Ω
30cm = 7.5 Ω
20cm = 5.4 Ω
10cm = 3.2 Ω
There is an unmistakable pattern of the resistance increasing as the length of the wire increased.
Analysis of graph
From the graph showing the resistance the pattern can be seen with all of the points rising steadily in a straight line, showing the increase in resistance was constant. Also a relationship can be seen where twice the length gives approximately twice the resistance. 40cm = 9.4 Ω and 80cm has a resistance of 17.1 Ω – approximately twice of 9.4 Ω. This is also the same for all the other readings that can be halved or doubled. The resistance reading from 30cm is 7.5 Ω, this is approximately a third of the 90cm reading, 20.0 Ω.
Conclusion
My results and graph proved that the resistance increased as the length of wire increased, which agrees with my prediction. There was a steady pattern with the results and graph which showed that I performed the experiment well and gained accurate results.
Evaluation
Overall, I feel that I gained very accurate results from the experiment, but there are always things that can be changed to make the results more accurate and less room for error. There were problems which I encountered during the experiment that could have made my results less accurate. One major problem was the fact that the wire could slack and so I may not have been reading the current for exactly the length of wire that I wished to. This could have been avoided by cutting each length of wire out separately, instead of just sliding the crocodile clips closer together. This would have given me the reading for the exact length of wire each time.
Other experiments could also be done to test other hypotheses. For example I would investigate how using different types of wire affects the resistance, by using other types of wire such as nichrome wire.
