Plan: From the preliminary experiment, it was found out that temperature doesn't affect the resistance of the wire so nothing special needs to be set up to keep the temperature the same. The experiment will simply be done at room temperature.
The potential difference will be varied using a different number of cells each time, and the length will be varied by cutting five different lengths of wire. The wire being used is Nichrome 28SWG and the different lengths being used are 10cm, 20cm, 30cm, 40cm and 50cm. Again, the resistance will be found using the formula and so the potential difference will be measured using a voltmeter and the current using an ammeter. The wire was connected to the cells and ammeter using crocodile clips on the ends of insulating wires. The wire will be suspended in the air by fixing the insulating wires to a stand and clamp so as to prevent the worktop from being burned. The lengths will be measured using a meter rule and readings will be taken with 1 cell, 2 cells, 3 cells and 4 cells. This will be repeated for each length of wire.
Safety: The only major safety matter in this experiment is the heat of the wire. From the preliminary experiment, it was found that the heat increases with voltage, and as the voltage will be increased in this experiment, great care will be needed when handling the wire. As can be seen from the preliminary investigation, with 5V, the wire is red hot, which if touched, would give severe burns so to avoid this, contact with the wire should be kept to a bare minimum, and not at all after the experiment is finished as this is when it will be hottest. Also, care should be taken not to let the wire come into contact with the worktop, as when red hot, the wire could burn and therefore damage it.
Fair Test: The independent variable of this investigation is the length of the wire, which will be changed by using different lengths. To keep the experiment fair, the diameter of the wire will be controlled by using the same each time, and the temperature will be controlled by doing the experiment at room temperature in a space of 20 minutes, to avoid any dramatic temperature changes. These measures are necessary as it is known that the diameter of the wire can also affect its resistance. The cells will be checked before the experiment to make sure they all work, as otherwise this would affect the voltage. The current and resistance will be measured to the nearest 0.01A and 0.01V to ensure that the results are accurate and each experiment will be repeated, and then a average will be found, to ensure reliability.
Hypothesis: A piece of nichrome wire is made of nickel and chromium. Electricity flows through the wire as electrons, but they do not have a clear path to flow through. This is because as they move through the wire, they hit the atoms of nickel and chromium. These atoms are the resistance that the electrons are said to have hit. This helps to make a prediction on the outcome of the investigation, as I think that as the length of the wire is increased, the resistance will also increase. This is because as the length is increased, the number of atoms that the electrons have to pass through also increases and as these atoms are the resistance, the resistance increases. I think that the graph of length against resistance will look like this:
This is because if the length of the wire is doubled then I think the resistance will also double.
SKILL O: OBTAINING EVIDENCE
The experiment ran quite smoothly and not much was changed from the original plan. Only, that instead of cutting five different lengths of wire, only one piece of wire was used and to make the five different lengths, the crocodile clips were placed at the ends of each length. This was done simply to save wire and not waste it.
The table below shows the results collected from the experiment and the calculated averages.
SKILL A: ANALYSING EVIDENCE
Below are graphs showing the averaged results, with voltage against current. The lines are of best fit, to show any anomalous results.
All these tables show that at each length of wire, the current increased in direct proportion to the voltage as all the lines go through the origin. The equations are of the line and the gradient of each line (y = gradient x + c) give the resistance, as the gradient is found by dividing the change in the y-axis by the change in the x-axis, and the resistance is found by dividing the voltage by the current, and the voltage is on the y-axis and the current is on the x-axis.
The table below shows the average resistance of each length of wire against its length. These will be plotted on a graph to be able to make a conclusion to this investigation.
From the graph above, we can conclude that as the length of a piece of nichrome wire is increased, the resistance is also increased, and if it was decreased, the resistance would also decrease. My prediction has proved to be correct because I predicted that the resistance would increase along with the length, and it has. The resistance increases with length because the number of atoms increases and therefore increases the amount of resistance against the electrons trying to flow through the wire. I predicted the shape of the graph, which is the same as what is shown above and this is because the resistance increases along with length.
SKILL E: EVALUATING EVIDENCE
Looking at the graphs, it is quite obvious that the results obtained were very accurate with any anomalous results having a difference of only 0.01A. As this is a very small amount of current, I think it is safe to say that there were no anomalous results, and therefore we can say that the experiment went well. The results could have been more accurate if digital voltmeters and ammeters were used instead of manual ones, as it is very difficult to obtain a result to any further degree of accuracy on the manual ones. Also, the measurement of where the crocodile clips were placed on the wire might not have been completely accurate, which could therefore have changed the results, as we have established that an increase of length increases resistance. As the wire lengths were not cut, and were simply made by using crocodile clips, there was a lot of excess wire, and while doing the experiment, it was noticed that when the excess wire moved, the voltage was changing, and so even though we were very careful to make sure the wire did not move, this couldn’t be guaranteed and so could have affected the voltage, which would then in turn have affected the resistance.
I think that the investigation could be improved if more accurate measurements were taken and it was repeated more, because then more wider differences between the figures could be more obvious and make the conclusion more reliable. If I did the same investigation again, then I would stick to my original plan of cutting five different wire lengths rather than using crocodile clips and moving them, because this might have caused anomalies. It could be extended by finding out the effect of the diameter of the wire on the resistance, and then the effect of varying both the length and diameter at the same time, as this might make the resistance double, or it might make it increase even more. Different wires could be used, to see how length and diameter affect the resistance of different wires to find out which type of wire would be the best to use, as its resistance would be least affected by varied lengths and diameters. We could also find out how temperature affects any other wires, as even though we established that it does not affect the resistance of nichrome, it might affect other wires.
