Current (A)
Prediction
In the preliminary the results are not as conclusive as would have been hoped but that’s where you can excel on testing. In the preliminary there were only three tests which were inconclusive, there needs to be a greater amount of tests to ensure a full set of results are obtained. It is also vital that different wires are tested as one wires result are sure to differ from that of another. In my experiment both Constantine and Manganin wire has been used. I feel that different sizes in the form of length and diameter both affect the resistance in a wire. I think that as the wires diameter increases the resistance will do the opposite and decrease. Increasing the diameter gives the electrons more of a free flow instead of that of a narrow wire in which there is only a small space for movement thus creating more resistance.
This diagram shows how diameter can affect flow of electrons. As you can see the top wire is much wider and has a lot of room for movement, whereas the bottom is a very thin wire and is congested with not a lot of room to move.
Variables
Each experiment should be tested more than once to make sure that the results that you have achieved are correct and there are no silly mistakes. At least 3 trials should be done with this kind of experiment as there are many positions that the rheostat has to be changed to, to get good, positive results that support the prediction. By moving the position of the rheostat, the resistance of the circuit will change, so the results will show different when the rheostat is in different positions and these can then be compared to the other trials for the other diameters of wire.
The independent variable for this experiment is the diameter of the wires. This is because the diameter of the wire is going to be changed constantly to show how it affects the resistance.
The controlled variables are the variables that are not changed. These conditions must remain the same throughout each experiment or the results will be inaccurate as the results have not been carried out in the same conditions. The controlled variables are:
- The same type of wire but which have different diameters.
- The length of the wire should always remain the same.
- The rheostat must always be kept in the same 3 positions depending on which trial you are testing.
The dependant variable for these experiments is the resistance. This is because the resistance will vary on how big or small the diameter of the nichrome wire is.
Apparatus:
Constantine Wire
Conducting wire
Power Pack
Rheostat
Voltmeter
Amp meter
Analysis of Preliminary
What it is visible from the table and graph is that generally the greater the Potential difference and Current the greater the resistance
My input variable for the actual experiment will be Diameter. I chose this for the same reason as for my preliminary work; because I have predicted at the beginning that increasing diameter decreases resistance. My other variables are length, temperature and type of metal. I will keep the temperature the same by checking that the temperature of the room stays at room temperature constantly. For length and type of metal I will measure the same length each time (1m) and make sure the label on the wire says Manganin wire. I am important that the wires do not accidentally change because different wires have different levels of conductivity. Also changing the temperature will increase the energy in the particles creating the heating effect. This will give invalid results. My outcome variable is resistance (Ω). I will measure this by doing the sum of Voltage/potential difference (V)
Current (A)
Apparatus:
Micrometer
Manganin Wire (5 different diameters)
Conducting wire
Power Pack
Voltmeter
Amp meter
Rheostat
Analysis
The graph shows that as the diameter of the manganin wire increases the resistance decreases. This proves my prediction because I claimed that as diameter increases the resistance should decrease. It has been proven very clearly. From 0.5mm to 0.7mm diameter the line of best fit changes. It has a gradient of 1.1cm.This is great compared to a gradient of 0.6cm at the diameter of 1.0mm-1.3mm! This shows that at around 1.5mm to 1.7mm of diameter is when the resistance really makes a difference. The line gets flatter towards the end of the graph. This could show that when a wire is spacious inside (has quite a big diameter) the electrons still do not pass through completely without resistance, at least not until a wire with an extremely large diameter, but that is to be experimented with in the future. There is one anomalous result. That is the result of diameter 1.2mm, which gave 1.3Ω. This may have been because the connections were not secured properly and had loosened over time. Or the wire was caught under a heavy object (like the power pack), which squashed the wire slightly, reducing its diameter. Except from those minor mistakes, which were corrected straight away, the results were extremely accurate.
Evaluation
The range of my results has given me a good set of results and I have drawn an accurate line of best fit. Also for each range three repeats were done. The reason for this was in case a slight anomaly that was not noticed occurred in the first experiment the result would be inaccurate and not valid therefore ruining the experiment. But by doing the experiment again and again assures that the results must be valid. When an average is found it gives you one accurate result! The method was good and worked for the experiment. It was a simple method. The circuit was a parallel one which is more difficult to construct than a series but it all worked out well. I do not think there is much that could have been done to make the experiment better or more accurate. Obviously the more space provided the better and more clear the circuit appears. More space would have been better.
I think that if the diameter were to keep increasing the graph would show that there is nearly 0 resistance. Although the curve is flattening towards the end of the graph I think it will travel right through to almost 0 resistance. To develop this thought/prediction my ranges in the investigation would have to increase by much more. The experiment just completed gave me curiosity over whether temperature would affect resistance. I think it would and the particle theory of temperature (giving the particles energy) may make a difference.