Type of wire: When I have chosen the wire I will be using (during my preliminary work) I will use this wire continuously throughout my investigation, as other different types of wire may have a different resistance to the one I have chosen which would distort my results.
Temperature: The temperature will have to be kept roughly the same as the atoms within the metal move faster if the temperature is hotter, this means that the free electrons inside the metal will be moving faster than they would originally be on a cooler day. If the atoms are moving quicker then the resistance will increase, as they will encounter more atoms that they will have to avoid on route to the positive terminal of the cell.
Number of cells: This is important, it will affect the resistance because as the wire becomes hotter then the resistance of the wire increases because the atoms within the wire will be moving at an increased pace (see information on temperature).
The type and thickness of wire, number of cells, temperature will be kept the same during my experiment in order to ensure that it is a fair test.
Independent Variable:
My independent variable will be the length of the wire as this is the variable that will be changing throughout the experiment. I have decided to start with a wire of length one metre, I will decrease the length by five centimetres each time, this should give me enough results to plot an accurate graph
Dependent variable:
The dependent variable is the resistance of the wire, as this depends upon the length, width and type of wire.
Method:
Using the circuit I have designed I will be able to test the different lengths of wire that I am using, simply by clipping them into this space. My circuit has been designed in order to make the change from one length of wire to another quick and simple. To make sure that I have got the length of the wire correct I measured it carefully with a ruler. After using one length of wire I cut the excess five centimetres off before using the shorter length of wire. This meant that by the end of the experiment there was not an excess metre of wire not being used. In my preliminary work I did not do this and measuring and attaching the wire into the circuit became a lot more difficult as the unwanted section of the wire became longer. In the real experiment I corrected this and cut the excess wire off. Although this meant it was harder to re-measure a specific length of wire the circuit was easier to work with.
Preliminary work:
My preliminary work is to find out which wire out of a range of wires I will be using for my experiment and the number of cells I should use in my circuit. In order to do this I set up the above circuit and tested various wires in it, I used two different constantan wires, and one copper wire.
My preliminary results show that the copper wire I have tested has such a low resistance that to get a result that I am able to plot on a graph I would have to use a lot more wire than I intend to use for my actual experiment.
In my preliminary work I have also decided how many cells I would be using, first of all I tried a power pack, this did not appear to be working so I switched it for three cells, these cells increased the heat of the wire so that the resistance became excessively large. I decided to use only one cell, this meant that the resistance became lower and I was able to handle the wire as it was at a normal temperature.
Controlling the experiment: The number of cells used in the circuit should stay the same throughout as if the cell is older then it will have a lower voltage than a younger cell, also the wires used to connect the components into a circuit should also stay the same. The same type of Ammeter and Voltmeter should also be used in order to fully control the experiment. The length of wire being tested should be measured accurately against a ruler and clipped tightly into the circuit. The experiment should also be repeated for many different lengths in order to get accurate results and so that picking out anomalous data is easier.
After my preliminary work I found that my original circuit was working well for this experiment. I have no need to change my circuit before collecting my real results.
In order to work out the resistance from the results of the Ammeter and Voltmeter I will use this equation:
Results:
☼ -- This result appears to be anomalous, as it does not fit in with the pattern running through my table (e.g. as voltage decreases the current increases) So I re-tested that length of wire and found the following results:
I will now draw a graph of my results, including the corrected version of the results for the 65cm length of wire.
Analysis:
The results I have collected from my experiment support my earlier prediction and show that it was correct. The resistance of the wire does increase as the length of the wire increases. The relationship between the two is directly proportional and this is shown clearly on my graph. The graph also shows that every time the length increases by ten centimetres the resistance increases by roughly 0.5Ω.
Because I have collected so many results this is easy to calculate whereas it would not be if I had only a small number of results. Also as the resistance increases the current decreases and the voltage increases, this is because a higher voltage is needed to send a smaller current through the length of wire because the resistance has increased and is opposing the flow of electrons through the wire.
As the length of the wire increases then the free electrons in the wire find it harder to fight their way through the atoms of the wire and reach the positive terminal of the cell, because there are more of the metal atoms blocking their way which means that a higher voltage has to be used in order to give them the energy required to get through the wire.
The man behind resistance was George Ohm and the law that he discovered, saying that that the resistance of a component depended on the dimensions and other factors that surrounded the wire, if these factors were not all equal then the resistance of the wire would change.
Evaluation:
I believe that my results are reliable because the smooth trend of the graph and the fact that there was a pattern in my results (directly proportional) and they increased uniformly, also all the points on my graph were close to the line of best fit. All these facts have led me to believe that the results are reliable and accurate.
My experiment seemed to go well as at the end of it I had only one set of anomalous data and a clear pattern through my results. Although I did not repeat my experiment more than once I did however, collect a large number of results, which I think proves the pattern to be correct.
I don’t think that anything about my experiment could be improved, as it seemed to go well although changing the independent variable and testing how that affected the resistance of the wire could extend the study. Extending the study would provide more results and further proof that resistance is affected by other factors than the length of the wire, such as dimension and temperature.
The dimension of the wire could be changed as if the dimensions of the wire were increased then I think that the resistance would decrease because the electrons would find it easier to get through the wire, because there would be more space for the stream of electrons to fit through without colliding with the atoms in the wire.
The dimension of the wire could also be very easily measured (as it is usually pre-measured when you get it) which means that the experiment would be easy to carry out.
The temperature may also affect the resistance of the wire, as the heat energy being given to the metal atoms would cause the atoms within the wire to speed up causing more collisions with the electrons and increasing the resistance of the wire as the electrons find it harder to get through the wire.
The temperature would be very hard to measure for a lab experiment, as the temperature would have to be increased at a standard interval and kept at that temperature until the wire was tested also the experiment could not be done on an ordinary bench mat as they tend to melt at high temperatures. Possibly some sort of heated container could be made, like a dry water bath. This would make the temperature easy to monitor and keep continuous. The extension of the study