This resistance occurs when the electrons, that are attracted to the positive side of the cell, bump into the fixed lattice nuclei of the material that they are flowing through. This means the path of the electrons is erratic as they are changing direction. The more material there is for the electrons to flow through the more fixed lattice nuclei there are. More nuclei mean more bumping and therefore higher resistance. Increasing the length of a wire will increase the number of lattices. A larger number of lattices mean more for electrons to bump into and therefore more resistance.
I could also conclude, though not as strongly, that when cross sectional area is increased resistance decreases. This means that thicker wire has less resistance than the thinner wire (Nichrome 28 the preliminary results, compared to Constantan 28) even when they were the same lengths. This would be because there is more space for the same amount of electrons to move in, so making the path of each electron less erratic. The less erratic the path the less resistance. The reason I cannot strongly conclude is that I only tried two different wire diameters.
My results do not correspond exactly with my predictions, but they do match reasonably well. I predicted that the length would be directly proportional to the resistance, and I have found that this is so. Not all of my points were reasonably close to the best-fit line and I found that I had some anomalous results, e. g. at 40cm and 50cm, the points are quite far away from the points. This could be due to inaccuracy, or overheating of the wire. Then, at 60cm, the resistance increases dramatically and continues to rise quite steeply. From 60cm, I think I am able to say then only 90cm is an anomalous result.
Evaluation I think that the experiment did not work very well. I say this because my graphs had some anomalous results and that my results did not support my predictions very well. I also think that my results were not reliable. My preliminary results did not give a graph of the same pattern as my proper results. I therefore would say that my results are not reproducible. If I were to do the experiment again I would just expand on what was already done. I would increase the range; the length of the wire, to say 2 meters or as high as was possible for the laboratory.
I would also change the number of results for instance measuring voltage and current every 5-cm rather than every 10 cm. I would repeat results as much as possible, for instance 5 times rather than 3. I think that to say that my results are very anomalous would be untrue. Although none of the results are actually on the best-fit line, none are too far off, except for 40cm 50cm and 90cm. With all this taken into account, I would say that my results strongly support a firm conclusion. The reasons for this are that there are a reasonable amount of results taken over a suitable range and that the results have been repeated.
The equipment that I used seemed suitable. The wire quite straight though not as straight as it could have been. The ammeters and voltmeters I used worked well and had good scales with easy to read markings. I would say that they gave accurate results. Also, I did not notice too much zero error on the meters (when the pointer did not go back to zero). There would be two pieces of alternative equipment that could be used. Firstly, the wire could be replaced with something thicker that would not bend as much and so would make for more reliable length measurements.
Secondly, the ammeter and voltmeter could be replaced by digital versions. This would eliminate some human error as the mechanical ones that I used could be misread if looked at from an angle. Problems I had in procedure were the wire not being straight and temperature of the wire increasing. This meant the experiment was a fair test only to a certain extent. To change the non-straight wire problem I would rub it with a flat-sided object, such as a hard piece of wood. This would straighten out some of the bends. To stop temperature effecting earlier results so drastically I would take reading as quickly as possible.
This would give the wire less chance to heat up. Further experiments that would extend this work could include varying cross-sectional surface area further (rather than only trying two) and seeing how different materials effect resistance. Voltage applied and insulating the wire could also be tried.
Yael Levey 11JS Physics Coursework 26/04/07 Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.