R = constant x length / area of cross section.
Once the apparatus is gathered and set up as above I shall begin my experiment. The power pack shall be set to 3V before I begin my experiment. I shall start with the contact at zero on the measurement. I shall record the current along the wire every five centimetres until I have got results up to around 50 centimetres. I shall repeat this three times and then I shall move onto my next wire. I shall make sure that each one starts at the same place and that it is on zero. I will not however move it to start at zero every time, as this would be alteration. If there is an amount still at the beginning then I shall carry on, as there is a chance that there is a small build up of resistance. I shall do the following procedures to the experiment in order to make sure that it is a fair test. After doing many preliminary experiments I have been able to find out what kinds of things affect the current and resistance. A factor that affects the resistance affecting the current is the temperature, however this is not such a big issue, so I will therefore presume that it will all be at room temperature (which I will check at the beginning and the end and note if there is a dramatic change) but within the circuit I will make sure that it does not over heat by being wired in for too long. I will also check the area does not change throughout a certain set of results, although I will be changing it for back up results it will not be changed while I am doing the set of results for a single length. By controlling the above things I should be able to receive a good amount of correct results helping my results to be more scientifically correct.
I shall record my results in a table and then shown them in a graph. If my results are to be correct, to what I had predicted, then they will show the current getting smaller as the length gets greater. I also know that with my other comparison using a larger wire the current should be bigger at each length than when I did the thinner wire.
Below is a graph portraying what I think my graph shall look like.
It is obvious that the top one is a curve decreasing in current, as the length gets greater, and soon levelling out. This means that the current is inversely proportional to the length, however if I wished to find out how current and length are directly related I would do as the bottom one says, it would be 1/current. 1/current obviously makes the line straight and probably running through the origin unless there is some build up at the beginning. Above is how my results should back up my prediction.
Results:
My results shall also be shown on graphs on the next page.
How the chosen factor affected the current:
From looking at my results and at my graphs it is clear to me of how my chosen factor (length) affected the current. As I had predicted as the length is increased the current decreases. I did not predict however the levelling out of the graph, this may be because as the length gets greater there is a certain extent to which the current can decrease to, and as it gets closer to that amount it begins to become closer and closer. This may also be because if there is a set current being pushed through and it cannot get below the current that is being supplied, so therefore as it gets closer the results begin to get closer as they cannot reach that amount of the current.
How well the prediction has been confirmed:
From looking at my results in both tables and graphs I can clearly see that the prediction I had made was correct. It was backed up in the fact that the current was constantly decreasing, this means that my set of results were correct. Although, as I have said above, I think that the levelling out of the graph shows that it is close to the minimum current. Looking at the graph for the thicker wire as I have done it on the same size axes it is clear that it is larger from beginning to end.
How results fit in with background:
From researching, preliminary experiments and of course my scientific knowledge it is easier for me to see how well the results fit in with the background information. The background readings as I have already explained were that of recording a thicker wire, and to see how the current changes on an overall basis. Looking at my results it is clear that from the background reading, of how the size affects the current, it is clear that when the wire was larger there was a larger current. Using preliminary experiments and my scientific knowledge I should be able to explain this. A factor to do with this is the fact that as the width of the wire is greater it is easier for the current to pass through, meaning there is less resistance, due to this it can flow through more easily and less current is held up. Thus also meaning that the battery has to put less power into sending the supply through the wire.
Experimental accuracy:
From looking at my results I feel that the accuracy was very minimal. However I feel that the few anomalous results in the third attempt for the 24 SWG wire were out of place. Especially those towards the beginning of the wire. They may have been odd for reasons such as the wire was getting rusty and as I had not rusted it towards the beginning I did so then and the battery had an easier time sending the current along. Another problem may have been the facts that as we were only using a battery that was not connected up to the power supplies it may have begun to lose power. Another problem may have been the position I started the contact in. If I had started it further back then it would have started at a higher current as there is less distance to push. This would’ve affected the whole set of results however due to a good first two sets of results the results still turned out predominantly good.
Experimental reliability:
I feel that after taking three separate results and an average for each wire I took sufficient amounts of results to back up my prediction. I feel that taking a set of results for an extra wire also helped the factor that I was investigating into and the prediction I had made. My only sets of very odd results were on that for my secondary wire and towards the beginning. As they are still fairly close to the original and when I found out the average it all worked out anyway. From looking at my graph however a few odd results were found lying a fair way off the line, this may have been due to my drawing of the line but it may just be mixed with the line and the few odd results on the secondary wire.
Procedure improvements and Experimental extension:
Due to a limitation of time in my experiment I was unable to extend my knowledge and add more into my course work. If I had more time I could’ve investigated resistance along with current. As current and resistance are closely related it would’ve been easier to compare results and I could’ve experimented on other factors, especially those that affect the current. If I had also had more time I would’ve made the following improvements to my experiment. I would’ve made sure that each and every wire had been sanded and made more efficient for the current to run along. I may have also made sure that before each time the battery was completely charged so that there was no reason for it to drop the results.
Another thing I might have done to my experiment with a great deal more time is extending it so that I could’ve made further work into the factors. I may have done a whole range of widths of wire in order to compare exactly how much change there is between an SWG in the wire. A more important factor that I would have altered is the components of the wire. If I had more time I could get a number of wires made by different materials, mixtures of both that conduct and some that don’t conduct at all. By doing this I could’ve also experimented further into the factors whether the same rules apply to different metals and alloys, it may have been that in some the thinner the wire the less the resistance. I cannot quopte anything for this however as I did not test it.
