Method
I will need: Wires A 1.5V battery A Ruler The wire of resistance at its largest length An Ammeter A Voltmeter
I will set up my apparatus as above. Due to the earlier preliminary tests I know that I cannot let the length of the resistant wire get any shorter than 15cm or otherwise it will start to heat up. Consequently I will start to take my readings from the voltmeter and ammeter when the length of the resistant wire is at 15cm. The wire will be attached to a ruler, so the wire only requires contact with the resistance wire and it will make the lengths more accurate. I will repeat this process of recording the results every 5cm up to 80cm- a total of 14 readings. I have chosen this as I feel it is a good range and will hopefully give me a better scope of results. To insure that my experiment is fair, I have already made sure that the wire does not heat up, which would make me be testing two factors instead of one. I will also use the same piece of wire throughout my investigation. To underwrite that the results I get are accurate and reliable I will repeat this testing three times and then take the average.
Prediction
I predict that my results will obeys Ohm's Law, which means that the current will increase in proportion to the voltage. Therefore if you double the voltage, the current will also double. I expect my graph of results to be similar to the one opposite:
I also predict that as the length of the wire gets larger so will the resistance. So a plotted graph of the resistance compared to the length would also go directly through the origin and therefore be directly proportional.
The reason for resistance in wire is because of the composition of the atoms such as copper, aluminium, of which a particular wire is made of and the arrangement of the atoms of these metals. When an electron passes through the wire, the electrons hit these atoms while making the journey from one end to the other giving opposition or resistance to the electrons. When this happens electrons move an electromotive force such as voltage, and in hitting these atoms, can also create heat due to friction of the electrons and atoms. So as in this experiment I have chosen to test the affect of resistance on different lengths of wire, I have come up with my prediction as when the wire is lengthened, the journey that the electrons have to take through the material is considerably longer and therefore the atom numbers would also increase making the resistance increases with length.
Results:
Below is the 1st set of results:
Below is the 2nd set of results:
Below is the 3rd set of results:
Below is the average resistance in ohms:
On the following page is a graph that shows the average resistance in ohms by the length of the wire on cm.
Analysis:
I have found out that as the length of the wire increase so does the resistance of the wire. The resistance and the length of the wire are directly proportional as the straight line goes directly through the origin, meaning that the wire at fixed temperature has a constant resistance. This is seen by looking at the graph, when the length is 35 cm the resistance is 4 ohms, when the length is doubled to 70cm, the resistance is also doubled to 8 ohms.
The graph of y against x is a straight line through the origin: y= kX
With that equation of y= kX you can say that when the length is 35cm the resistance is 4 ohms, so then what is the length when the resistance is 9 ohms would be worked out as below:
y= length
X= resistance
k= constant of proportionality
35= k x 4
35/4= k
8.75= k
y= k x X
y= 8.75 x 9
y= 78. 8cm
Which looking at my graph display that this is correct, but it only shows it in whole numbers, not to 2d.p.
Consequently my prediction is correct is stating that the wire and its resistance are directly proportional also that if one is doubled so is the other. This is because as the length of the wire increases there is more material for the electrons to travel through and also more arrangements of atoms. Thus making it harder for the current to flow through and increasing the resistance.
Evaluation:
As my results came out as I had expected that alone shows that they are fairly accurate. The best line of fit goes directly through the origin with the points not very far away from the line at all. I did not get any anomalous results, I feel this is because I worked accurately throughout the practical and I also repeated the experiment three times and took the average resistance of them. When working I followed my method exactly and carefully, and order to make sure it was a fair test I followed the rule of using the same equipment each time the practical was carried out.
I feel that the only way that I could have improved the practical to maybe make all the results exactly on the best line of fit would maybe be the aspect of the ruler. This is because contact with the wire placed on the ruler was only needed to record the results. This may have been where some errors or inaccurate readings were taken. So maybe measuring each piece of wire and cutting it to the required length rather than using the same piece and just changing the point of contact.
This evidence does support a firm conclusion as if someone was to repeat the same investigation I would expect the to receive the same results.
If I were to re-do the experiment, I would test the same factor again, but maybe test a larger range to see whether the pattern that I recorded in this experiment would be repeated. Or I could perhaps test a shorter length but as my preliminary results showed that the wire increased in temperature I would have to add a variable resistor. However I could change the factor I test altogether- I think I would pick to change the type of wire that the resistance wire was made of.
