I did a pilot test to find out which wire would be best to use out of Iron, Nichrome and constantan. During the pilot I found out that it is important not to let the wire over heat, so if I want to get fair results I will need to keep the voltage low. If the wire gets too hot heat energy will be given off and the resistance will increase. The diameter of the wire I will be using is 0.27mm. This is because the thicker a wire is, the more room there is for the electrons to travel through it, this causes an increase in temperature, making less resistance which will make my test unfair and my results not accurate. The resistance of a thinner wire would be high and difficult to measure, and again my results would be less accurate.
To ensure that the investigation is carried out correctly and my results are accurate the only variable will be the length of the wire. The wire must be pulled tight against the ruler, ensuring that the correct length is measured. The investigation should also be repeated 3 times and an average should be taken to make sure the results are true and there are no flukes.
I am using a Nicrome wire because from a previous pilot investigation I know that Nicrome is the easiest and fairest material to use and it has a good resistance and is used in heating elements of electrical fires.
Pilot to find the range of lengths I will use in my real investigation
From my pilot experiment I now know that the safest and easiest range to use is from 10cm to 90cm, for the final investigation I will increase the length of the wire from 10cm to 90cm in steps of 10cm. This will give me 9 different lengths.
Method
*Set up the equipment as shown in the diagram on page one.
*Using the ruler measure a distance of 10cm between the crocodile clips, making sure the distance is in the exact middle of the crocodile clip. (If this is not done then the length will not be correct)
*Set the Voltage to 2V and measure the current from the amp metre and the other Voltage from the Voltmeter.
*Then change the voltage to 3V, then 4V doing the same as you did when using 2V.
*Once this has been done turn off the electric from the power socket and readjust the crocodile clips so the distance is 20cm, again change the volts from 2 to 3 and then to 4, measuring the current and voltage each time.
* Do this 9 times starting with 10cm and working up to 90cm, making sure the length is exact and the electric is turned off when adjusting the length. (This will stop the wire from heating which will affect the results)
*Once this has been done divide each volt by the amount of current, giving you the resistance. Then for each length take the three resistance results and average them so for each length you will end up with one average resistance.
Results
Analysis
Using my results table and graph, I can see that when the length of the wire increases, so does the resistance. My graph shows a positive gradient and that the resistance is directly proportional to the wire length. For example, from my results table I can see that if the length of the wire is 10cm the average resistance is 1.6 ohms and when the length of the wire is 20cm the average resistance is 3.8ohms. This makes a difference of resistance of 2.2ohms and when the length of the wire is 30cm the average resistance is 5.7ohms. The difference resistance between 20 and 30 cm is 1.9ohms. I can see from my graph that there were no anomalous results.
My results support my prediction. This is because I said as the length of the wire increases the resistance increases directly proportional to the length of the wire. The line of best fit on my graph shows that the results are directly proportional because the results are very close to the line.
However, I cannot be sure that my results are 100% true because there were some experimental errors. My wire was not in a dead straight line and although I tried my best to measure the length perfectly I cannot be sure that the length was exact. Also as the length of the wire decreased, the wire heated up, causing more collisions so the resistance was probably slightly increased.
Evaluation
I think my investigation went very well. Using my method I have found out that as the length of the wire increases so does the resistance. I also managed as far as possible to measure the length and resistance accurately. The results on my graph are generally on if not very close to my line of best fit.
I feel that my results are as accurate as possible. I took three sets of results and averaged them. Each set of results were very close but again I cannot be 100% sure they are exact due to the experimental errors mentioned in my analysis I also noticed that the crocodile clips were approximately 3mm in width and I cannot be sure that the length was measured in the exact middle of them.
If I was to re do the experiment I would make sure the wire was stapled perfectly straight. I would take more results to average and I would use a wider range of volts, keeping in mind that the more volts used the higher the temperature of the wire would be and the greater the resistance put on the wire, which would effect my results.
If I followed all of these adjustments correctly I would expect more stable and accurate results so my results plotted on my graph would all be on if not closer to the line of best fit.
