To choose which factor I am going to investigate I am going to consider how I would measure each factor and which factor would be the best and easiest to record. To measure the wire width I would use different widths of the same length and same material of wire e.g. thin, medium and thick copper wire with thin and thick constant in wire. To record the difference in widths I would use the same voltage and measure the resistance for each thickness. Although it would be easy to obtain and record the data the graphs that I would be able to draw up would not be interesting. For the temperature of the wire I would not be able to carry out a fair test because it is extremely difficult to produce and control the range of temperatures needed without the correct equipment. If I chose to measure the difference in the resistance in different materials I would chose a number of different materials and using the same voltage I would record the resistance given by each wire of the same length and width. Although once again it would be simple to record these results the graphs that could be drawn would not show any connection between the material and the resistance because of the limited number of materials I could test with the equipment available. The final factor is the length of the wire. To measure and record the findings for this factor would be simple and the results collected could show a connection between the length of the wire and the resistance given by the wire. This is why I have chosen to investigate this factor.
Prediction
I predict that if the length increases then the resistance will also increase in proportion to the length. I think this because the longer the wire the more atoms and so the more likely the electrons are going to collide with the atoms. So if the length is doubled the resistance should also double. This is because if the length is doubled the number of atoms will also double resulting in twice the number of collisions slowing the electrons down and increasing the resistance. My graph should show that the length is proportional to the resistance.
Method
To start with I will set up the apparatus as per the diagram below, when testing I will use a ammeter/voltmeter in order to find out the resistance and also see any currant change, I will use the formula R=V÷I. It is important that the ammeter is placed in series with the power supply and wire load and that any variation in currant is read on the ammeter with varying lengths of wire. In this experiment I will use thin wire that will be used to investigate the factors affecting the resistance of wire to collect the data for my graph I have chosen to take a range of 5 lengths. I have chosen a range of 5 as to plot an accurate graph I will need at least 5 points to mark on the graph. I have also chosen to take 3 repeats at each length and then take an average. I have chosen this so that if I have any anomalies in the results then they will not show when I plot the averages on the graph. The lengths that I have chosen are as follows: 20 cm, 40 cm, 60 cm, 80 cm and 100 cm. I have chosen these lengths because they are easily measured by the meter ruler and give a good range.
Apparatus
Meter ruler, selection of wires with different lengths but the same width, crocodile clips, voltmeter, ammeter, wires, bunsen burner, heat proof mat, clamps, bunsen lighter, power pack, copper.
Fair test
To ensure a fair test I shall keep the power supply at 6 volts and I shall keep the type of the wire as copper and the thickness thin.
Variables
My only variable is going to be the wire length.
Diagram
Results
Below is a table of results, which I have collected from my experiment.
R=V÷I
Conclusion
In my prediction I said that: “I predict that if the wire length increases then the resistance will also increase in proportion to the length”. From my graph I have shown that my prediction was correct, as the line of best fit is a straight line proving that the resistance of the wire is proportional to the length of the wire. The length of the wire affects the resistance of the wire because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion. The resistance of a wire depends on the number of collisions the electrons have with the atoms of the wire, so if there is a larger number of atoms there will be a larger number of collisions, which will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is increased the number of atoms will also increase.
Evaluation
From my results table and graph I can see that my results that I collected are very reliable. I know this because my results table does not show any individual irregular results, which means that I did not have to leave any results out of my averages because they were irregular. Also on the graph I can see that none of the averages plotted are irregular because all the averages lie along the same straight line. During my experiment I have noticed several alterations I could make have made to improve on the investigation if I was to repeat it, most of these alterations would be to the circuit, so I could have more accurate results. The first would be to use a connector wire with very low resistance as not to affect the overall impedance. The second to the circuit to keep the connecting wires as short as possible in order not to get voltage drop down the wire as both of the above could affect the results making them less accurate and therefore creating irregularities.