To make the results as trustworthy as possible, I have decided to perform the experiment 3 times. The same process will be taken out 3 times and therefore the results will be more reliable. Also, I think that by working out the resistance to a total of two decimal places will provide more accurate results. To get these accurate results the voltage and current will have to be found to two decimal places as well, to ensure that the resistance is found to two decimal places. To keep this experiment as accurate as possible the length of the wire must be measured precisely. We must also make sure that the wire is straight when we conduct the experiment. If it is not, short circuits may occur and bends in the wire may affect the resistance.
After performing preliminary work to find the most suitable material for the main experiment, and the most suitable thickness for the main experiment, I have decided to use thin constantan for the main experiment. This is because this combination gave the largest range of results and other materials contained many more anomalies.
To ensure safety the main thing is to use dry hands when handling anything electrical. Also, you shouldn’t keep the equipment on for too long; this is because it can cause energy loss which will also give unreliable results.
The diagram of the circuit below shows the full experiment that is going to be taking place.
The red line represents the variable piece of thin constantan. The crocodile clips are represented by black boxes. The voltmeter is set up in parallel to the circuit and the ammeter is set up in series inside the circuit.
Method
- Draw a table to collect the raw data, i.e. the length of wire in the circuit, the voltage and current.
- Set up the circuit as shown in the diagram above.
- Start with 100cm of thin constantan and record the results of the current and voltage readings shown on their respective instruments.
- Move the crocodile clips down 10 cm, measuring the 10cm accurately.
- Record the current and voltage and repeat process for the remaining wire lengths up until 10cm.
- Work out the resistance using the formula resistance equals the voltage divided by the current.
Analysis
By looking at the graph, the results show to us that there is an obvious relationship between the length of the wire and the resistance. The bottom axis represents the length of the wire increasing steadily by 10cm. As the length increases the resistance increases as well, at no particular rate. The line of best fit shows a steady increase in resistance of the wire as the length of the wire increases. From the graph we can see that the increase is constant. This is shown by the line of best fit which is drawn in a straight line. The markings representing the results are very close to the line to show the results are very accurate.
Also, the numerical data, of which the graph has been formed, shows that the resistance of the wire is directly proportional to the resistance. This is shown by the resistance doubling as the length of the wire doubles. I.e. when the length of the thin constantan is 10cm, the resistance is 2.36, and when the length of the wire is 20cm, the resistance is 4.12, showing that the resistance nearly doubles.
The graph has been created upon the average of the three attempts made, making the graph more reliable. I think that the graph is not most accurate. This is because the results were found to two decimal places. The graph shows the results to one decimal place. This could be overcome by having twenty squares for each ohm instead of the ten shown.
Conclusion
By looking at the graph primarily, I can see that my prediction stated in the planning section is correct. The graph shows that the resistance increased as the length of the wire increased.
Also, the resistance changed in proportion to the length of the wire. This is because as the length of the wire increased the electrons as part of the current, were forced to travel through more fixed particles in the wire. This caused more collisions between the fixed particles and the current. Therefore there was a higher resistance.
Evaluation
To perform the experiment we had to set up an appropriate circuit that would enable us to quickly and efficiently perform the experiment without changing too much. All the components of the circuit were kept where they were. The only thing that I moved during the whole experiment was the crocodile clips. These were moved by 10 cm along the 1m long piece of thin constantan. This was quite easy to set up and once we got started we had to do nothing else to record results. The only problem in setting the experiment up was the fact that the constantan used was very thin. This was a problem because it made connecting the circuit slightly more difficult and making sure everything was held place was also difficult. We didn’t need to make any modifications to the circuit as it worked properly from the first time and in the preliminary tests.
The results obtained from the main experiment were very accurate. However, individual results were not as close as I would have hoped it to be but we had already found out from preliminary tests that thin constantan had a large range of results. For example, from the third attempt the length of wire is 10cm and its resistance was measured at 2.79, but the average was only 2.36. This shows the large range of results. The graph shows that the results follow, as predicted, a straight line. Although the line is not dead straight, the results are very close to the line meaning we can’t really say there were anomalies. None of the points actually lie on the line of best fit; this is because the line is in the middle of all the points so there are an equal amount of points on both sides.
I think that the method that I used in the experiment was very good. There were good points such as that fact that once everything was set up, i.e. the circuit, very little had to be done in order to obtain results. This was a good thing as it saved time and reduced the amount of energy loss. Also, the circuit was well organized so the results could have been said to be very accurate and reliable. The only weakness in the experiment was the fact that the crocodile clips were too big for the thin wire. This made it hard for the clips to hold on to the thin wire. Next time I think that I would fix one end of the wire with tape to the clips. This would ease the procedure and make the results quicker to obtain. To make the results more reliable next time, I think that I would reduce the number of other wires used (to connect the other components in the circuit). Most errors in our experiment were seen when we measured the wire. This is because it was not very easy and practical to hold a piece of wire straight along a ruler while trying to fix crocodile clips to the wire. I don’t think that the crocodile clips were always fixed securely to the wire with a good connection and this is what I would change for next time.
The results shown in the numerical data sheet shows that the data was very accurate and must be reliable. All the results are constantly good and accurate. An example of this is in the three attempts for 90cm of thin constantan. The three resistances obtained were 17.40 ohms, 17.60 ohms and 17.60 ohms. The three results are very close indeed with two of them being the same. The graph can also be used as evidence to show that the results were reliable. All the points are very close to the line of best fit. The only reason why I think that the results may be unreliable is the fact that the material may not have been as pure as hoped for. This, however, may not have affected the overall answer in any way.
The results that were obtained from the main experiment can definitely be used to make a firm conclusion from. The line of best fit and the numerical data can be used as evidence to support the predication made by myself in the planning section. I predicted that the resistance would be directly proportional to the length of the wire, and this is shown by the line of best fit. The theory that I stated in the conclusion is also supported by the graph and its line of best fit.
I think that doing three more repeats was enough to obtain satisfactory and reliable enough results. I would not say that doing more repeats would get more reliable results. Instead, I think that maybe, in place of using wire that easily bended and caused disruptions to the results, maybe a bar would have worked better and more efficiently. This would have got more reliable results.