I decided I would have the length as my independent variable and the length would vary from 200mm to 1000mm. I had the resistance as my dependant variable.
The experiment circuit:
Preparing for Practical
Before I started the actual test, I needed to decide what material to use and what voltage to have on the power pack. The voltage on the power pack goes from 2-12 but I decided to set the power pack voltage to 2, because any higher and the wire would have gotten hot therefore making it a safety hazard. I chose nichrome for the wire material because in the textbook table below, it shows that Nichrome had the biggest change with the increasing SWG compared to the others, so if I chose nichrome the results would be wider and they would be more interesting. Copper does not have a very large gap between each result so if I chose copper, the graph would have virtually no error bars and the results would not be interesting to take down.
In order to make my final decision I did some trial tests myself. I set up my circuit and tested Nichrome, Constantin and Copper. I didn’t test Tin because the school did not have any available.
Nichrome:
These are good results, that would be good to put on a graph and show a clear correlation. However the results didn’t change a great deal so the error bars would not be easy to draw on.
Copper:
These results are not very reliable because the voltmeter wasn’t working properly and the results were hard to read. However I had already decided not to do copper at this point because of the data in the textbook and these results just confirmed that decision.
Constantin:
These results are unexceptional , the results do not show anything in particular which told me that Constantin would not be a good material to use because the results would be bland and not of proved anything. So I decided to use Nichrome as my material.
Investigation
Equipment:
- Wires to connect circuit
- Voltmeter to measure volts
- Nichrome wire to test
- Power pack for the electricity
- Ammeter to measure current
I set up my circuit, like the one on page 2, and then performed the experiment, I performed the experiment twice to make sure it was a fair test and my results were reliable, and if I did the experiment twice it would mean I could get two sets of resistance results therefore I would be able to work out the average resistance and plot my graph well.
First Experiment:
These results seem to me to be accurate. They show a correlation, for voltage, the higher the length the higher the voltage, and for current, the higher the length the smaller the current. This makes me think that my results, for my first experiment are reliable. I included the resistance in this table because putting the resistance in on this first table made it easier for me when I came to draw up the resistance table because the resistances were already worked out. I knew it would make it easier for me which is why I did it.
Second Experiment:
This table also shows accurate results with a clear correlation. These two tables put together show my results are accurate and reliable because neither of the tables have an outlier and the almost mirror each other in the actual results. With these two sets of resistance results I could now draw up my resistance table which is below.
My resistance table further proves that my results are accurate and reliable because the resistance also has a correlation, as the length increases so does the resistance, also there are no outliers on any of the tables and I did not need to repeat any results. All of this also proves that I carried out my experiment and investigation as a whole correctly and got the results. Also because I performed the experiment twice the results for the resistance table are more accurate and reliable because they were worked out twice, also this means I could draw my graph.
Graph
My graph proves further still that my results are reliable and accurate because all results apart from one sit on the line of best fit. The one result that doesn’t is the result for 900mm, it is an outlier but only by a tiny amount, this outlier may have been caused by a number of things, for instance, it could have been an error on my part in taking the results down or measuring it, or it could have been a fault in the measuring equipment such as the voltmeter or ammeter. I also know all my other results are correct because there is a correlation on the graph, as the length increases so does the resistance. You can see this on my graph at 200mm and 400mm, because as the length doubles, the resistance also doubles. My resistance for 1000mm is 10.48Ω, the textbook answer is 9.26Ω so you can see my results are fairly accurate because there is not a big difference and they are within 15%. I have drawn markers on my graph to show the doubling with 200mm and 400mm and also a marker for the 1000mm result.
Conclusion
In conclusion I think my results are both accurate and reliable. The only evidence to suggest otherwise is the one outlier on the graph at 900mm however, that is only one result out of 10 and was most likely caused by a fault with the voltmeter or ammeter also you can only see this outlier on the graph it is not big enough to stand out on any of the tables and all the other results I have collected prove strongly they are accurate and reliable as on all the tables and on the graph there is a clear correlation. On the graph, all of the results fit clearly and easily on the line of best fit except the outlier I have mentioned, this also proves my results are correct. Also the results that I got are very similar to the textbook answer; in fact one of my results is within 15% of the textbook answer. These factors also help to prove I carried out the experiment and investigation correctly and got strong, reliable and accurate results.
Evaluation
I believe I have carried out this investigation well and have collected a very good set of results. There are areas I could improve, for instance, if I was to do the investigation again I would do the experiment 3 or 4 times to make sure I had a fair test and I would do 2 or graphs to eliminate any outliers and to get the textbook answer. I would also try to test all four materials, (Nichrome, Constantin, Copper and Tin) because I did not get to test Tin so I do not know if I could have gotten better results with Tin than Nichrome also if I had been able to test Tin it would have made it more of a fair test because I would have made sure Nichrome was completely the best material to use in the experiment. I would like to have tried a higher voltage to see what effect that would have had on my results however I would not of been able to go up too much higher otherwise it would have been an unsafe experiment. If I were to do it again I would also test Copper and Constantin 2 or 3 times to ensure Nichrome was the best to use. However I think my experiment as it is has proven the resistance of wires and has answered my title therefore achieving its purpose. I believe I have explained and justified all my decisions in my investigation and in my opinion these decisions aided the outcome of the investigation. As a whole I am confident in my investigations outcome and believe I have identified all the problems I had with this experiment and explained the reasons they happened and how I solved them. I have also explained what I could have done to improve my experiment and have explained how my results are accurate and reliable and what in my experiment proves my results are accurate and reliable.