Choice of Factor
I have chosen to investigate length as this is the easiest of the four and I believe that we will get the best set of results by doing length. I will be using the wire constantan 22 as this is a very good wire at maintaining a constant temperature, I choose grade 22 as this was the thickest and it heated up the least on my preliminary investigation meaning that it will not be affected as much by temperature in the experiment and so keeping my readings as accurate as possible. Temperature in a wire would be very hard to measure as it would be difficult to alter the temperatures. We could do type of wire but then other factors like temperature come into it as some could heat up more than others, hence altering the resistance.
I predict that the longer the wire the greater the resistance will be I make this prediction with the scientific knowledge that as it is longer the electrons will have further to travel. Also for this to be correct then we should also be seeing that the resistance is directly proportional. Double the amount of wire should have double the amount of electrons and double the amount of collisions, so therefore a piece of wire 20cm long should have double the resistance of a piece of wire that is 10cm long.
Equipment
- Power pack connected to the mains
- Meter ruler
- Constantan wire
- Ammeter
- Voltmeter
- Crocodile clips and connecting wires
- Tape
Circuit Diagram
Method
I will begin by measuring out a piece of constantan 22 to the length of 100 cm. I will then tape this to either end of the meter rule to keep it safe and secure; this will also help me for when I need to measure to obtain other results. Then I will set up the circuit as shown above. To take my results I will first decide the length I am going to do and connect the crocodile clips at this length, and then I will alter the power pack to get 0.7amps on the ammeter and then record the reading on the voltmeter. I will repeat this for the five lengths I am measuring and then repeat all the results for a second time.
In order to make it a fair test I will use the same piece of wire for measuring the 20cm, 40cm, 60cm, 80cm and 100cm, only changing to get my other set of results. I will always use the same current of 0.7amps and I will use the same connecting leads for both experiments.
To make this experiment safe I must ensure that the power is not turned up to high; this will cause extreme heating of the wire making it dangerous. Basic lab rules must also be followed to make sure of a safe experiment.
Results
Analysis
Line of best fit Graph
Conclusion
From the graphs we can see that as the length increases so does the resistance. This is exactly what I predicted would happen. The results on the graph are directly proportional to each other for example if we look at 40cm and 80cm, 80cm is roughly double that of 40cm. The reason for it not being more accurate can be accounted for by the 2% of inaccuracy allowed for the ammeter and voltmeter. Also the fact that we cannot guarantee the exact length of the wire due to kinks and bends in the wire also counts towards inaccuracies. The results I have acquired are extremely good; if we look at the graph we can see that there are no results far off of the line of best fit graph.
Evaluation
I am fortunate in the way that I do not have any anomalous results that need be ignored; all of my results are very good. If I had had any anomalous results it would have been best to repeat them so as to get a full set of results.
My results were very accurate and mirrored a straight line; the line of best fit is not much different to the line which connects the points. The two factors that were out of my control that might have contributed to inaccuracies were the ammeter and voltmeter, both had a 2% degree of accuracy which means some results taken could have been slightly inaccurate. Another factor that could have caused inaccuracies would have been that the length of wire could not be exact as it was very hard to get it straight, it had bends and kinks in it making it longer than what was measured. If we had the proper computer equipment we could have gotten past this as a computer could take into consideration any kinks and bends hence giving us the exact length. Because of the accuracy of my results they have enabled me to make a firm conclusion.
In order for me to improve my investigation I would expand the number of readings I took. Instead of taking just 6, I would take eleven readings, 0cm, 10cm, 20 cm etc. This would give a much better range of results. To give more accurate results I would have it so that we used more accurate equipment, like the voltmeter and ammeter, also it would be better if we could measure the wire more accurately, in order to give us more accurate results. In order to extend the experiment readings could be taken with different currents rather than just 0.7amps.
