Variables and Fair test
To ensure that the investigation is carried out in a fair way and that the end results are accurate and reliable, a number of points must be followed.
The only variable in the test will be the length of the wire as it is the only piece of apparatus that is going to be changed constantly throughout the experiment.
To keep it a fair test, the wire must be pulled tight against the ruler and taped in place to ensure the length is accurately measured when reading off it. Also, the same circuit and battery must be used throughout the test as different batteries may have different voltages if they are older or have been used more. We must also keep the room temperature the same, because particles in the wire will move faster if the temperature in the environment surrounding it is increased. This is because more heat is transferred to the particles inside the wire which causes them to vibrate more. More importantly, the material of the wire must be kept the same as different materials have different conductivity.
These last two factors will be kept the same by using the same wire all of the way through the experiment.
Diagram
Method
1.
When I have all the necessary apparatus, I will set up the experiment in a circuit (as shown in the above diagram).
2.
Starting off with my wire length unchanged at 100cm, I will turn on the power supply. I will note the readings from the ammeter and the voltmeter. Using the Ohm Law formula, I will divide the voltage by the current, which will give me the resistance. This represents the actual resistance of the wire when it was manufactured.
3.
I will resume the test and start to measure my first length. To do this, I will simply move the voltmeter’s variable point to the next length on the ruler. This is a very efficient method to measure different wire lengths with the same piece of wire. Its advantage is that it will save time and resources as I will not have to keep creating new pieces of wire and sticking them down to the ruler to make sure that they are the right length. I just have to move the variable point of the voltmeter to measure a different length.
4.
For each wire length I will take the ammeter and voltmeter reading. The reason for this being so that I can calculate the different resistances for the lengths at the conclusion of the test using Ohm’s law.
This will be repeated until I have got recorded current and voltage results for each length up until a 100cm.
5.
This test will be repeated three times to increase their accuracy and reliability, and will ensure that there are not any anomalous results.
6.
Using Ohm’s law I will work out the resistances for each length (as I have the current and voltage for each length).
7.
I will work out the average for each resistance by using the mean.
To calculate the mean of a set of data, you have to add up the results, and then divide the total by the actual number of results.
I will take a large range of measurements so that there can be a good spread of results. This would aid me to arrive at a good conclusion, which is accurate.
I have also increased the accuracy of my results by performing repeats for all my experiments, so that the average will make a more accurate results table. By graphing the results, I will be able to see any anomalous results.
Results & Analysis
My results show that the higher the voltage, the lower the current and I believe that this true for all of the results. Because I have compared my data with three experiments I believe that all of the data is accurate – though, the 50cm experiment on the third test is slightly out of place. This can be put down to a unique error in the reading of the result or a sudden fault in the voltmeter. However, the most probable cause of this irregular result is the change in the surrounding temperature. Temperature affects the resistance because if the wire is heated up, the atoms in the wire will start to vibrate more rapidly. This will cause more collisions between the electrons and the atoms due to atoms moving into the path of the flowing electrons.
Now, I will find the resistance for each test as I have the voltage and current. After working out the resistance I will find the average of the resistances. Taking the average is a more accurate method of measurement of a wide range of readings. I will work out the resistance using the formula R=V/I. I will calculate the averages by adding up the results and dividing by how many results there were- in mathematical terms, I am calculating the mean average of the data.
To analyse my results further I will plot some graphs. Consequently, I will use my data to draw a conclusion that is accurate and reliable.
My graph to show the resistances of test one, shows a nearly perfect straight line. This shows that my results were accurate as there are no anomalous results which can be clearly seen in the graph. This also goes along with my prediction that a nearly perfect straight line would appear from my results. This is because the data which I have gathered has a resistance which is directly proportional to the length of the wire. In this experiment, my prediction that the longer the wire is the more the resistance is true. When the length of wire is 10cm, the resistance is 1A. But, when the length of the wire is 50cm, the resistance is just over 6A.
My graph to show the resistances of test two also shows a near perfectly straight line. There are no anomalous results which are visible in the graph. This also, like the previous graph, goes along with my prediction that a nearly perfect straight line would appear from my results. This is because when the length of wire is 10cm, the resistance is just over 1A. But, when the length of the wire is 50cm; the resistance is just over 6A. This result is similar to the test I did in the first experiment.
My graph to show the resistances of test three, again, shows a near perfectly straight line. However, this graph does straighten out into a small plateau in the middle. This small plateau (50cm/5A) shows that there were no results out of place, which in-turn suggests that this result was therefore anomalous. Overall, my graph shows that my results were accurate as there is only one anomalous result which is clearly visible. Like the other two charts, this one also goes along with my prediction - that a nearly perfect straight line would appear from my results. This is because the data which I have gathered has a resistance is directly proportional to the length of the wire. In this experiment, I predicted that the longer the wire is - the more the resistance. When the length of wire is 10cm, the resistance is 1A. But, when the length of the wire is 50cm, the resistance is just over 5A. This is a different result to the other two charts which I have produced. It also looks out of place on the graph, so I will ignore this result when I am writing my conclusion.
I will now compare all three of my result graphs. I will do this by plotting them onto the same chart with their average.
Conclusion
My graph(s) show that there is a very strong positive correlation. This means that when the length of the wire increases, the resistance also increases. The results are also directly proportional, meaning that when one doubles so does the other. An example would be at a wire length of 50cm where my results show that the resistance is just over 6 ohms, and at 100cm it is just over 12 ohms. As you can see, this is almost exactly double the size. My prediction has been clearly justified here.
The line of best fit clearly shows that the results followed the expected pattern very well. The points are very close and some are even touching the line. This shows how the results were directly proportional throughout because the gradient of the graph remained the same and also shows the accuracy of the results.
Evaluation
In my experiment, I have an anomalous point at one main point. However, there is not a suitable theory that I can put towards the reason for the anomaly being there. This is because the anomaly is right in the middle of an experiment, and has occurred very suddenly. Therefore, I can only put the anomaly being there down to fluke and chance.
I think that my results are accurate enough evidence for my conclusion as I repeated my experiment 3 times with the same piece of wire to make the results reliable, and then took the average of these three tests to make the results more accurate.
Most errors in my 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. The next modification I would make would be to use pointers instead of crocodile clips to attach to the wire. I would do this because pointers would be more accurate as the tips have a much smaller area than the crocodile clips, giving a more accurate measurement of the length of wire. Also, in the experiment, I did not control the room temperature but instead just assumed it was keep constant throughout my experiment; this could have made the wire get hotter and therefore making my experiment not as accurate. In future experiments I would control this variable factor and make it a constant factor. I would do this, as it would be an unfair test if there were two known variables.
As well as making these modifications, I could also expand on my investigation by testing the same wire but different widths of that wire. I think the circuit and method used was suitable as it was very time efficient to work with. However, if I had time, I would do the experiment again but changing the separate lengths of wire each time.
