It appears that if the diameter of the wire is increased the resistance goes down. This is because there is more space in the wire for the free electrons to move thus, there are far fewer collisions, bringing the resistance down. It is from this test that we have decided to use Nickelchrome – 0.19mm. This is because it seemed to give us a good low result. We do not want to be using a wire that would be giving us very minute or massive results.
Key Factors
When investigating how varying factors affects the resistance of a wire we found quite a few factors that can be varied. Below I have listed the main factors and detailed information, pros and cons about these factors.
Temperature When the temperature of a metal increases the resistance of that metal also increases. This is because when the temperature increases the atoms of the metal vibrate more vigorously because of the increase in energy. This means that the electrons have more difficulty getting through the wire as they collide with the atoms that are in their pathway. This increases the amount of collisions therefore there is more resistance. However it is hard to keep the temperature exactly the same as the room temperature might change from day to day. It is essential to use a low voltage because it means a low current that will not heat up the wires. If a high voltage is used the energy would be in form of heat which would make the experiment unfair. The investigation will be done at room temperature. The temperature cannot be investigated because it is hard to control the range of temperature needed without the correct apparatus. Also there are only so many accurate variations you can investigate within a classroom, and once a substantially high temperature is reached you may not have the equipment to achieve higher temperatures.
Length The longer the length of the wire, the larger the resistance. This is because there are more atoms from the metal so there is more chance that the electrons would collide with one of the atoms therefore there is more resistance. Electrons have a longer distance to travel so there are more collisions .The length of the wire will make a difference to the resistance. This is because when you have a long wire, the electrons have to squeeze together for longer than they do in order to be able to pass through a short wire to be able to pass through the longer wire. I predict that the longer the wire, the greater the resistance. If I had a 30 cm wire and a 60 cm wire, the 60 cm wire would have a resistance twice that of the 30 cm wire.
Material Different materials have different resistances because the materials’ atomic structures are different so some metals have low resistances and some have high resistances. Therefore it is important to keep the material the same throughout the experiment unless a different material is used to check if the conclusion or theory works for all materials. If different materials are used throughout the investigation, it will affect the results. For example if sometimes copper is used and sometimes nichrome is used, the results where copper is used will be of a low resistance because of the material and not because of the diameter of the wire. Also when using wire you are limited to the amount of variation you can use, as there are only so many elements you can use, with length the variation is infinite.
Diameter When the diameter of the wire is varied it becomes difficult to cover a wide range of results as the range of diameters available for us is very limited. After a certain amount of diameters have been covered it would be hard to find a wire with a huge diameter, and especially at an affordable cost for the school.
After considering the four main factors that can be varied I have decided to vary the length of wire, and monitor how the resistance changes as the length of wire is varied. The reasons I have chosen length of wire is because of the following:
- By varying the type of wire this doesn’t give me a continuous variation, I am limited to only the few materials available to us.
- By varying the temperature of the wire this is a very difficult factor to maintain, it would not be possible to take an accurate temperature of a piece of wire in a classroom. The variable range would have to be high to even approach an accurate procedure.
- To vary the diameter would also prove to be difficult. This is because there is only a limited amount of different diameter wires of the same type available. Also if we decided to double wire up this would also prove to cause hassles because We would be limited to how many times we could double it up because of the amount of students, and the amount of wire.
- It’s very easy to do because it’s very repeatable and the conditions are easy to recreate.
- After 1M the variations in resistance are very good for further analysis.
Prediction
I predict that from the results I gain in the final experiment I will derive that as I increase the length of the wire, the resistance will increase proportionally. This means that as the length of the wire increases the number of free electrons in the wire also increases. Therefore the chances of the fixed molecules in the material colliding with the free electrons are higher. And the more successful collisions there are the higher the resistance.
Diagram:
Method
- We will set up the apparatus as shown and then begin to conduct the experiment.
- We will take the resistance every 10cm from 0cm to 100cm.
- Once we have a clip attached to the wire at 0cm we will then place the other one at 0cm also.
- Once the resistance has been taken at 0cm, we will then move the crocodile clip up the wire 10cm, and take a reading. I will then continue to move the clip up the wire 10cm at a time and take the resistance until I reach 100cm.
We would now like to conduct a second method using the same wire. This method will be to prove the results we will gain while conducting the first method. The second method is as follows:
Diagram:
Method:
- We will set up the apparatus as shown and then begin to conduct the experiment.
- We will take the voltage & current every 10cm from 0cm to 100cm.
- Once we have a clip attached to the wire at 0cm we will then place the other one at 0cm also.
- Once the voltage & current has been taken at 0cm, we will then move the crocodile clip up the wire 10cm, and take a reading. I will then continue to move the clip up the wire 10cm at a time and take the voltage & current until I reach 100cm.
Fair Test
For both methods I will keep all but one thing the same. The one thing that will change is the distance between the two crocodile clips. Although I am keeping all but one factor the same I still need to decide how I'm going to keep these factors the same.
- Circuit Design: I will maintain the same amount of current the whole time, and I will ensure that the temperature does not change in the environment during the experiment.
- Wire Diameter: I will measure the wire’s diameter every 20cm for 1M with the micrometer to ensure that the wire’s diameter remains constant.
- I will ensure the wire is completely faultless, with no sharp bends and joins. This will ensure that the results will be constant no matter which point a result is taken from on the wire.
Safety
With these experiments there is not much of an issue with safety. I have outlined the 2 main safety issues:
- Ensure the PSU works properly and all wires are insulated fully.
- Do not secure the wire too tort because if it snaps it could whip you in your face.
Results
The resistance in the second experiment was calculated using ohm’s law. I have noticed that the resistance readings of the wire using both methods are very close together. They show close comparisons all the way through both experiments.
Conclusion
From my results I conclude that my prediction has been proven that as I increased the length of the wire, the resistance increased proportionally. This means that as the length of the wire increased the number of free electrons in the wire also increased. Therefore the chances of the fixed molecules in the material colliding with the free electrons were higher. And the more successful collisions there were the higher the resistance.
Attached is a graph. This graph shows the increase in resistance as the length of wire was increased during both methods. From my graph I have shown that my prediction was correct, as the Lines of Best Fit are straight lines proving that the resistance of the wire is proportional to the length of the wire.
The length of the wire affects the resistance of the wire because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion.
The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a larger number of atoms there will be a larger number of collisions that will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is increased the number of atoms will also increase proportionally. For example when a wire of material x is 50cm long is contains 2y amount of electrons. When the wire is doubled in length, the number of electrons in the wire also doubles meaning that there would then be 4y of electrons in the wire.
Out of my two sets of results I can see a more accurate set in one compared to the other. In the experiment using the method that did not include the power supply we took the reading of 0.04Ω for the resistance of the wire at 0cm. This is definitely incorrect and there is no distance of wire between 0 and 0cm. Also with the method using the power supply a realistic and practical current is passed through the wire using a separate source to the reader, giving a more accurate reading. My graph results also show that the method without a P.S.U. seems to give inaccurate results. This is because some of the results at the beginning of the experiment are showing not to follow the pattern of the other set and do not stay close to the best-fit line.
Evaluation
Experimental Error and Improvements
During this experiment I had one anomaly which shows that our method and results were relatively accurate. The anomaly showed a resistance of 0.04Ω but logic says that there is no wire to pass current through to obtain this result. Therefore because this reading was necessary it then led us into error by attempting this ridiculous reading. This anomaly could have been prevented if certain procedures used in this experiment we changed. These features are:
The taking of a reading at 0cm. I feel that it was not necessary to take a reading of resistance at 0cm. It is obvious that no current can pass through 0cm of wire. The readings should have started at 10cm.
The use of crocodile clips. If more accurate probes had been used when adjusting the length at which we took readings then the prevention of any anomalous results and the guarantee of accurate results could be sure. This would be so because the pointers have a much smaller surface area ensuring that the pointer is placed in the exact place intended.
Certainty
Although I acquired one or two anomalies I feel that these were due to the problems described above. But disregarding the anomalous results I still managed to prove my prediction, which was that as the length of the wire increases the resistance of the wire also increases proportionally to the length increase. I also know that my results are accurate because my resistance readings for 1metre are very close to the published manufacturer’s data. The recorded official resistance of Nickelchrome at 1m is 35.6Ω. I took the readings 40.00Ω and 40.80Ω. These results are very close, showing accuracy in my investigation.
Investigation Variation
This experiment produced good results with scientific proof of the results. But to back up the prediction and final result further tests could be carried out to eliminate any possible room for error.
A variation I had in mind for this investigation would be to do an extension experiment investigating other factors considered in the planning of this investigation. The next appealing factor to vary is the diameter of the wire. The prediction for this is that as the diameter increases the resistance should become lower because of the collision theory. As the diameter increases there becomes more space between the free electrons and fixed molecules therefore there will be fewer successful collisions meaning lower resistance.
I could have also worked out the resistivity of this investigation and compared it to the published data. The equation for resistivity is R=pl/A. Using this formula you can work it out. Resistivity of s wire is proportional to its length. The resistivity of wire lets you work out a wire’s resistance suing only is length, area and thickness.
