I am going to measure the voltage of the wire as the length is varied. The lengths of the wire that voltage will be measured at are from 10cm to 100cm with the wire changing length by 10cm every time e.g. 10cm, 20cm, 30cm etc.
A 100cm piece of 32-gauge wire will be laid out on a ruler and the crocodile clips will be attached to the wire while laid out on the ruler so that I don’t have to cut separate pieces of wire for every variation of length in the wire.
Fair Test
The things that will be kept the same are:
The circuit’s wires because if they are changed they would be different lengths therefore it will affect the resistance of the circuit so I wouldn’t be a fair test.
The diameter of the wire must be kept the same because if the thickness were different each time, there would be more or less atoms that the electrons would have to travel through therefore it would decrease or increase the resistance making my results unreliable.
The temperature also has to be kept constant because the calculations depend on this. This is shown in Ohm’s law. If the temperature is varied then the electrons in the wire would vibrate more or less and this would make it easier or harder for electrons to get past the atoms in the circuit and this will directly affect the resistance.
Also the make up of the constantan wire needs to stay the same, the wire that we are using is:
55 % Copper
44 % Nickel
1 % Manganese
Because each of these elements have different sized atoms so other wires with different compositions would have different sized atoms and this would make it easier or harder for the electrons flowing around the circuit to travel through the wire and this would affect the figures of the resistance.
I also have to make sure that the wire is fully tort so that the length of the wire is accurate. The current needs to stay the same because if it was increased the resistance would decrease and if the current was decreased the resistance would be increased therefore it would affect my results. If the current was varied it could increase the temperature of the wire dramatically and this would increase the resistance and also affect the results.
Accuracy
The measurements of the voltage and the current will be accurate to 2 decimal points.
I will do the experiment three times and take the average of those results to make sure my results are reliable. My experiment is a good way of doing the experiment because it is accurate, reliable and it follows a law of physics to work out the answer, which is an unbreakable rule. The measurement of the wire will be accurate to the nearest millimetre because it will be laid out accurately on a ruler.
Preliminary work
I carried out a Trail experiment and these are the results I obtained:
These results were the basis for my hypothesis because there was a relatively steady increase of results of about 0.86 – 0.92Ω every time the length increased. This was done poorly because the wire was not laid on a ruler when the experiment was taking place so the measurements of the wire could have been slightly off.
In the first place I tried to use 1 amp as my current, but there was not enough room on the variable resistor for me to adjust it to this current, so instead I used 0.5 amps. When I used this current it worked for all the lengths of the wire without any unnecessary heating of the wire which would affect my results.
Results
The resistance was worked out using the equation R = V/I
i.e. resistance for 10 cm = 0.5/0.5 = 1 Ω
The thickness of the Constantan wire of 32 SWG and 0.28mm diameter is constant throughout the experiment.
The graph of these tabulated results are shown on the next page.
Conclusion
My results, including the graph, show that that the line is straight going up in the graph, positively; therefore the resistance increases constantly as the length of the wire increases. This straight line shows us, therefore, that the resistance of the wire is proportional to the length of the wire.
Taking in all of the results and the calculations it shows that the more wire added increases the resistance this is because, as there is more wire there are more atoms that the electrons flowing in the wire have to move past therefore the resistance on the current increases, this increase in resistance is shown every 10cm in Figure 1.4.
Figure 1.1 shows this evidence so as wire is added on there should be the same amount of atoms being added on so the resistance should increase at a constant rate but this is only by assuming that there is the same amount of atoms in every 10cm of wire. This is not possible but if the amounts of atoms differ slightly, it doesn’t affect the results in any major way. These results agree exactly to my hypothesis, this is shown as a perfect set of results that show the predicted proportionality exactly with the line of best fit going precisely through the origin of the graph.
Evaluation
My experiment was a good way of carrying out the experiment because it was safe e.g. didn’t have a high current that could be dangerous.
It was a complete fair test with no overlooked factors and there were enough results were taken to show a detailed pattern of the resistance increase. All the resistances were measured accurately with electrical equipment to 2 decimal places. I used precise measurements. I have enough results to draw a valid conclusion to make sure that there is an accurate line of best fit and it describes it in enough detail. There is also a wide range of results up to 1m to make sure that there is no change in constancy of the resistance. My results are reliable because the have been repeated 3 times and the averages of those results are used in the graph. There were no anomalous results in the experiment to discuss because they were a perfect set of results.
Improvements
I believe that my method was the best one because I got absolutely perfect results showing the predicted proportionality with a line going straight through the origin and it had very accurate results with enough repeats to ensure that the results were reliable
To provide evidence for the theory in the hypothesis you could test different thicknesses of wires. When the electrons in the circuits hit the atoms in the wire it makes them vibrate so the wires heat up so you could set up an experiment to find out the temperature of the wire as the current increases, this would prove that the electrons hit the atoms. For further work I could try and keep the temperature of the wire at a constant level because the current in the circuit would heat up the wire and this in turn would increase the resistance, so I have thought of another experiment.
When the wires experimental length has been decided I could keep it in a bath of water, where water will be coming in and going out constantly replacing the water to keep a constant temperature. The water must be distilled so that it does not conduct electricity to affect the resistance.