After working out the Voltage and the current, I will work out the resistance using the equation R=V/I. To find out the resistance, I shall complete the experiment once and record the first sets of readings, then repeat the experiment and record the second sets of readings. Then I shall take an average of the Voltage and Current from the two sets of readings and use the averages to work out the Resistance. Finally, I then drew a graph of the results showing the length of the wire against the resistance.
Further Work:
Resistance depends on the size and shape of a material e.g. if it is long or thick, it has a greater resistance than a short or thin material. However, we must take into account that the property of the material also affects the resistance. The relevant property of the material is its resistivity. In order for me to further my work, I shall need to work out the resistivity at the same points on the wire I worked out my resistance for.
I shall do this by using the formula= Resistivity X Length
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Cross sectional area
I can re arrange this formula to show:
Resistivity = Resistance X Area
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Length
The graph above is shape of the graph that is expected because if you double the length of the wire, you’ll double the resistance, because you will be increasing the amount of collisions between the electrons.
Results:
Analysis:
The significance of my graph is that it shows that as the length of the wire increases, the resistance does too. This graph clearly shows that they are directly proportional. My results match my prediction as I said that if you double the length of a wire, you would also be doubling the resistance at the same time.
From the table above, you can see that every time you double the length of the wire, you also double the resistance. This happens because if you double the length of a wire, you double the number of electrons in a wire, which means that there will be more collisions hence, the doubled resistance.
The results are to be trusted as when the average was taken, readings from both the first and second attempt were close to each other. All of the points on the graph are spread out over the page and all the points either lie or are within touching distance of the line of best fit.
Evaluation:
I feel that overall our results were quite accurate. This is can be seen when we look at the graph, which shows a straight line with all of the points apart from one being very close to or on that line. The one point that was not that close to the line was a slight anomaly, but it was only slight and did not affect the final gradient of the graph. I have found out that for the wire I was using, the resistivity at 20©C is 4.9 X 10-7 ohmmeter. From this we can then work out the percentage error of our results:
The accuracy for this experiment is, theoretically, ± 15.7%, but as one can see this does not seem to be the case from looking at the graph. The reason for this could have been due to a number of different factors. Firstly the temperature of the wire was not necessarily 20©C when we conducted the experiment and the material of wire may not be as pure as it should have been. The main reason for this was probably due to the equipment that we used being inaccurate. This did not stop us from seeing the trend, though, because the equipment would have been out by a constant amount each time therefore there was a constant error. So the trends that were predicted in the plan still were shown.
Most errors in our experiment were encountered in the measuring of the wire. This is because it simply was not very practical to hold a piece of wire straight, whilst holding it next to a ruler and then trying to accurately fix crocodile clips to the right part on the wire. Also I do not feel that the crocodile clips were always fixed securely to the wire with a good connection. This also meant that they were easy to move about on the wire changing the length of it. Errors rarely occurred in the setting of the current and the reading of the voltage. It was just in the preparation area that they did occur. Another example of this is the wire was never totally straight when we started the experiment, which may also, as said earlier on, affect the resistance of it.
I do not think that doing any more results in our experiment would have made it any more accurate. I feel that the only way to make it more accurate would be to use a different method – perhaps were we had a bar that did not bend in place of the wire. We could even use a rheostat in place of the wire, because it is essentially a long coiled wire that is connected at different lengths to change the resistance of the circuit.
Further investigations that could be done in the future are looking at the relationship between the resistance and the cross sectional area of the wire using a micro gauge meter.
