Table 3 (Varying Length) – SWG 28 Material SWG Thickness (Diameter in g) Length (cm) Reading No Current (A) Average (A) Resistance (? ) Constantan Table 4 (Varying SWG/Thickness) – Length 10cm Material SWG Thickness (Diameter in g) Length (cm) Reading No Current (A) Average (A) Resistance (? ) ConstantanNickel Chrome Nickel Chrome Nickel Chrome Nickel Chrome 30 125 70 1 0. 8 Nickel Chrome Nickel Chrome Table 6 (Varying Length) – SWG 32 Material SWG Thickness (Diameter in g) Length (cm) Reading No Current (A) Average (A).
R 7 Analysing results My results support my predicted statement: The thinner and longer the wire the high the resistance and lower the current.The thicker and shorter the wire the lower the resistance and higher the current. As the length of the wire increases and the thickness decreases, the resistance increases and the decreases. As the length of the wire decreases and the thickness increases, the resistance decreases and the current increases. I have calculated the gradient of each graph to prove the relationship between the current and the potential difference. Apart from the graph for the first table, all the rest show that it slowly rises and then a steep increase follows. The steep increase indicates that the wire is resisting or controlling the current.
These graphs show the variation of resistance with temperature. In general, an increase of temperature increases the resistance of metals but decreases the resistance of semiconductors. We can see that constantan and nickel chrome wires act as thermistors at a certain temperature. The resistance of most thermistors decreases if their temperature rises, i. e. their I – V graph bends up, as shown in the graphs. These graphs undermine my prediction that my results in turn should produce a straight-line graph. Except for the first graph, all the remaining ones are similar. However, the first graph obeys the Ohm’s law whereas the others do not.
‘Metals and some alloys give I – V graphs, which are a straight line through the origin… so long as their temperature is constant’. This statement relates to the first graph only. This graph supports my prediction, which is that my results in turn should produce a straight-line graph. However, although constantan and nickel chrome are metallic conductors and are alloys they do not give a straight-line graph. The graphs show us that these wires do act as thermistors. They are not ohmic or linear conductors. The gradient of the graphs except the first proves this. If the gradient was the same or near enough the same, for example, 0.
1 difference, then that would prove that constantan and nickel chrome are ohmic conductors. Conclusion The aim of my investigation was to investigate the factors affecting the resistance of a wire. By looking at my results I can tell that there is a relationship between the resistance and the a) Length of the wire b) Thickness/SWG of the wire c) Type of material (resistivity). My prediction that my results will produce a straight-line graph and secondary source of data from ‘Letts Science Single and Double Award’ and ‘GCSE Key Stage 4 Longman Study Guides Physics’ do not support my results except for the first graph for table 1.
Graph 1 was constant. Other graphs were curved showing that the material acted as a thermistor. My background information supports this. The resistance of the wires varied with the temperature, which also shows why my preliminary work went wrong. As I was moving the sliding contact of the rheostat I was varying the temperature. More resistance meant less current, which meant lower temperature; less resistance meant more current, which meant higher temperature. This also shows that it was acting as a thermistor. Part of my prediction was proven to be correct and is shown in my analysis of results.
However, the other part of my prediction was proven to be incorrect due to my misunderstanding that constantan and nickel chrome obey the Ohm’s law. This is also shown not only in my analysis of results but also in my graphs and by calculating the gradient. Evaluation To improve my results, I could have got a second opinion in reading the reading on the ammeter, to ensure that I had not misread it. When I cut the piece of wire I did not check it again to make sure that it was the correct length. The wire was bent as it was obviously wrapped around the reel.
Again, this affected the accuracy of the length of the wire. Therefore, my results were not perfectly accurate. My teacher also helped me during the experiment. I knew what to do but somewhere my results did not seem correct. There was no constant pattern. However, there was a small pattern in the results in between them. Otherwise they kept on increasing and decreasing. The reason why my results were affected in my preliminary work was because instead of keeping the resistance on the rheostat constant it was being varied along with the length or thickness/SWG of the wire.
My results did point out an odd result. My first graph obeyed the Ohm’s law by producing a straight-line graph. Strangely, the rest of the graphs produced curved graphs, indicating that they act as thermistors. I would have understood if all the graphs for constantan would be straight-line but it was only one graph of varying length out of three graphs of varying length. The reason for these odd results can be justified by saying that as the resistance increases the energy is converted to other forms of energy, such as heat and light energy.
This increases the temperature as the energy is converted. This causes the substance to act as a thermistor as the temperature exceeds room temperature and it is being changed. My results are sufficient enough to support my conclusion. The reliability of my results is quite good as I have a good range of results to support my background information and prediction. It was beneficial that I took a range of readings because just in case there was a loose connection and I did not recheck it, my results would be incorrect. Therefore, it was a good idea to take three readings of each result.
This way I could see if I made a mistake. My method was quite suitable. However, to improve this I could have put the piece of wire at the end of the clip so that the accuracy of the length would not be varied or changed. To extend my investigation another experiment can be devised. Due to the fact that at room temperature the thermistor has a high resistance, its resistance falls when it is heated. It gives a lower resistor, a larger share of the battery voltage. This in turn will make the bulbs light up. Thermistor (e. g. TH3)
By putting the thermistor at the top of the potential divider the total resistance will fall because the temperature will rise. This will mean that the voltage will get bigger. If this further extended improvement proves correct that means that the bulb will light up. We will know if this works by calculating the resistance and plotting a graph, which should produce a curved graph for a thermistor. 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.