- If the wire is thicker there is more room for the electrons to flow through. That would result in less resistance due to less successful collisions. A thin wire would have more resistance due to the fact that there is less space, so there would be more collisions between atoms and electrons. Due to the fact that they would collide with each other more often the resistance is higher.
- A bigger current in the circuit would result in more resistance again due to the fact that the free electrons would have more energy to collide. A smaller current would mean less resistance due to less energy
- If the temperature of the wire is hot, the atoms would vibrate in their fixed positions at a higher rate. This would lead to more collisions with the travelling electrons. More collision would result in a higher resistance.
The only variable that I will be changing in the above list is the Length of the wire, because that is what my experiment is about, but I will experiment with more than one wire, just to really prove if my prediction is correct.
PREDICTION!
I predict that as the length of the wire increases, so too will the resistance. My reason for predicting this is that the longer the wire becomes, there is an increased chance of free electrons colliding with other free electrons, and the metal particles. This will mean that more energy will be lost as heat, therefore increasing resistance. I also predict that as the length of the wire doubles, then the resistance should double because it means that double the wire means double the resistance, which in turn means double the energy, double the collisions, (between the free electrons, particles in the metal and other free electrons) double the energy lost as heat, and ultimately double the resistance within the wire.
EQUIPMENT!
- Multimeter x 2
- Meter ruler
- Connecting wires
- Crocodile clips
- Wire board
- Battery pack
METHOD!
To conduct the experiment, I will make the circuit like in the diagram. The ‘A’ is the Ammeter, which measures the current flowing through a circuit. The ‘V’ is the Voltmeter, which measures the potential difference across a component, which in the experiment is the wire. The circuit will obviously have two battery cells, so that it has power to conduct the electricity.
I will choose one wire, which will be the same material and diameter so that the test is fair. . I will measure the resistance of the wire by recording the reading on the Ammeter and Voltmeter then dividing them by each other to get the resistance. I will record the results correct to two decimal places. I will increase the length of the wire by 10cm and find out the resistance again. I’ll do this up to a maximum length of 80cm. I will then repeat experiment twice to find the average of the resistance in my test.
FAIR TEST!
To ensure that my experiment is fair, and therefore accurate, I will not change the material of the wire because if I changed the material of the wire, the different materials of wire will probably have different amounts of electrons, therefore changing the outcome of the experiment. I will not change the width of the wire, because again if the wire has more or less width, there will be an increase or decrease in movement of electrons. I will try to make sure that the temperature of the wire stays at about the same temperature, because and increase or decrease in temperature would mean the increase or decreases in movement of electrons due to more or less energy. To do his I will take out the battery so that it does not overheat the wire, and increase the temperature in the wire. I will however be changing the length of the wire, and that would enable me to see if the length of the wire affects the resistance or not.
SAFETY!
To ensure the safety of myself and other pupils, I will but my coat and bag in the allocated storage space, and therefore meaning they are out of the way, and it minimises the risk of someone tripping and falling and injuring him or her or breaking equipment. Also I will push my stool under the desk so that I won’t sit on it and people won’t trip on the stool leg as they pass. To stop the wire heating up, I will disconnect the battery after each result is recorded, this minimises the risk of the wire heating up, or something burning. I will be careful as not to break any equipment, so I shan’t run in the classroom this minimises the risk of me falling or breaking something.
PRELIMENARY RESULTS!
In my preliminary results, it shows that as the length of the wire increases so does the resistance, and as the length of the wire doubles, the resistance doubles, which means that the resistance of the wire is proportional to the length.
ANALYSIS!
TABLES OF RESULTS.
This is my first table of results for the resistance of a wire. As you can see I have tested the same wire twice, so that the results are varied. The resistance increases as the length of the wire increases, just I said it would in my prediction. However, although the results are proportionate, they are not directly proportionate. For example, take the 4th result. The resistance is 1.86Ohms. At 80cm it should be 3.72Ohms but it is 3.67 Ohms, which is less than predicted.
TABLES OF RESULTS
These are the results for the second wire that I tested, and re tested. As you can see, some of the results as with Table 1 are proportionate, but not directly proportionate. This wire was thinner than the first wire, therefore there would be less space for the electrons to move about and therefore there would be more collisions which would result in more heat energy, and thus more resistance.
The results can be explained using Scientific Knowledge. As I explained earlier on in the project, electrons within a wire, flow from a negative to a positive. On the way to the positive side of the wire, these free electrons will collide with other atoms and the free electrons. The more reactions that occur mean that the more atoms there are in the electrons ‘way’ of getting to the positive side of the wire. As the length of the wire increases, there will be more and more collisions, meaning more resistance in the way of the free electrons trying to get to the positive side. Its like if you come back from the Metro Centre during the rush hour. There is a long stretch of motorway before cars can turn off, therefore if you want to get home, you will have to wait for the congestion to die down. The longer the road, the more cars there are in the way of you getting home. The energy wasted by the cars goes into the air as gaseous fumes. Just like in a wire. The longer the wire, the more atoms there will be in the way of the free electrons getting to the positive end of the wire. The wasted energy is the heat, which is the resistance.
CONCLUSION!
I can say that quite evidently in both wires that I tested, as the length of the wire increases, the resistance follow suit. For example, using the first table, the first result for wire one has a resistance of 0.52 Ohms, which was measured at 10cm. As the length is increased to 80cm, the resistance has increased to 3.67 Ohms. That is an increased resistance of 3.15 Ohms. On the second wire, at 10cm the resistance is calculated at 0.89 Ohms, which is an increase of 0.37 Ohms. At 80cm, the resistance is calculated at 6.98 Ohms, which is nearly double that of the calculation for wire one at 3.67, so there is an increase again on wire two of 3.31 Ohms.
Obviously the results from wires one and two were going to differ because of the fact that the second wire had a smaller diameter than the first, allowing more heat to be generated when the free electrons collide and react with the particles of the metal and other free electrons, therefore more resistance is created too.
I have looked at both of the graphs, and without a doubt I believe that the table for wire 1 is far more accurate than wire two, as it has a smaller range, as the average resistance differences ranges from 0.43Ohms (2.29 Ohms) to 0.52 Ohms, (0.52 Ohms). In the case of this wire, the resistance does increase the more the length is increased by. The lowest resistance is 0.52 Ohms, and the highest is 3.67 Ohms
On the second wire, the differences in the results are more varied. The average resistance differences ranges from 0.52 Ohms (3.19 Ohms) to 1.66 Ohms, (2.67 Ohms). The lowest resistance is 0.89 Ohms, the highest resistance is 6.98 Ohms, which is nearly double that of Wire 1’s final result.
In a nutshell, the resistance increases on the second wire because the wire has a smaller diameter, therefore that allows for more free electrons to collide with the particles of the metal and other free electrons, to cause heat, which is the resistance.
EVALUATION!
In my opinion the experiment worked well because I achieved what I set out to do at the very beginning, which was to see whether increasing the length of a wire, would affect the resistance of the wire (which now conclusively I can say it does).
Wire 1 I don’t think obtained any anomalous results, which is why I believe it to be more accurate than the second wire, even though the second wire had a smaller diameter, which would give it the increased resistance. Wire 2 had two anomalous results, at 50 cm’s and at 80cm. My theories as to why I have obtained anomalous results are explained below.
There are some anomalous results in the experiment. I did not expect not to get anomalous results. When the resistance was higher than expected it is plausible that I measured too much on the wire, therefore increasing the resistance. When the resistance was too small, it is also possible that I measured too little, which would result in a smaller resistance. The measurements of the wire were not always correct.
The crocodile clips that connected the circuit to the wire slipped and it
was difficult to get the clips into the right places. Not that I want to blame the anomalous results on school equipment, a factor that can’t be denied is that the wires were not new or perfect. They will have been used for other experiments. That is the reason I decided to knock a kink out of the first wire. As a result the second set of results showed on the whole a greater resistance. As I stated in my variables, one of the factors would be the temperature of the wire. As more tests are done on the wire, the temperature will increase due to the current flowing through it and as a result some tests on the wire were done when the wire was at a higher temperature than it was for others, therefore resulting in increased heat and more resistance.
If I were to do the experiment again, I would probably experiment on the wires four times instead of two so that I got a larger variety of results, allowing me to have more data to analyse. Another thing I would do would be to take more care when measuring because the fact that I didn’t measure them properly means that the experiment was inaccurate. I believe that it would have been better if the wires were cut into 10, 20,30,40,50,60,70,and 80cm pieces. That would save me having to measure the wire and the results would be more accurate. The wires might also be straighter if they are smaller, because they won’t bend as easily. I would also prefer the experiment to be spread over two lessons because in testing two wires twice, which equates to four really, I did not have the time to continually take the battery out and put it back in like I said I would, in the beginning. That is why I also said that wire 1 was more accurate than wire 2. If I were to repeat the experiment again, I could have used a computer to record the results. This would rule out human error in being too slow to stop the stop clock once there is a reading. Using a computer would also I presume speed up the experiment so that more tests could have been done on wires?
