Find out whether the length of the wire affects the resistance in a circuit.

Physics Coursework: Resistance

Aim: To find out whether the length of the wire affects the resistance in a circuit.

Planning

Before the experiment, and the set up of the circuit, I plan to play around with the variables, which include the voltage, and the length of the wire to determine what setup I can use for the experiment that will give me a good and distinctive resistance level. To make this a fair experiment I aim to have potential difference of 3 volts for each of my wires and I will measure voltage and current every 10 cm’s for 100 cm’s, if I do that for all of my wires then I can be sure of fair results. I do understand that a heated metal does not obey ohms law and therefore you can argue that if I have a potential difference of 3 volts rather than 2 volts which will heat up the wire, but I will only have the current flowing through the wire for a very short period of time so therefore I can have 3 volts. I will test a thin wire, and a medium wire to see the difference the thickness makes to make sure that my theory works on any thickness of wire; therefore I can be sure that I can be sure that the theory works on any kind of wire. The equipment I will need is:

5 Leads to connect to the various components.
2 Multimeters, one set to be an ammeter and one to do the job of a voltmeter.
A nichrome wire on a meter ruler.
2 crocodile clips to complete the circuit.

Between the readings, I will switch the power off so the wire does not get hot and increase the resistance further. I will take 20 readings, 10 for the first time and 10 again for the second time. When collecting my results I will make a graph of averages. I choose to do 100 cm’s and measure resistance at every 10 cm’s to show how much it increases from 10 to 100 cm’s.

For every 10 cm’s I will record the voltage and the current, with this information I could work out the resistance using ohms law.

I predict that the resistance in the circuit will go up steadily as the length of the wire increases.

My prediction graph shows what I predict the resistance will increase as the length increases. This is because there will be more atoms for the flowing electrons to bump into, therefore slowing the current and increasing the voltage, current, being the initial push that the electrons get will slow down, and so there will be more voltage which is like the store of electricity to push the electrons through the atoms, more voltage and less current ...

This is a preview of the whole essay

I predict that the resistance in the circuit will go up steadily as the length of the wire increases.

I think my plan is reliable because I will have control of the voltage from the power pack and that will always be the same.

Above is the circuit diagram for my experiment. Where the arrows are drawn there will be a crocodile clip to attach the wire to the circuit.

Observations

To carry out this experiment safely I followed some basic rules, the rules were not to touch anything without insulation like the nichrome wire for instance when connected and the crocodile clips when attached to the wire could be dangerous. Also any water was kept well away from any electrical equipment to ensure maximum safety.

I observed my results twice; I recorded the voltage and the current so that I could work out the resistance using ohms law for the two wired that I performed this experiment on. From these results I could work out the averages. The averages of the three wires that I did are shown after the individual wire results. My precision and skill was good, I made sure the wire was fairly tight, but not too tight, so that the accuracy of my length was fairly accurate, one cannot tighten the wire too much as I found out, you will not be able to attach the crocodile clip to the wire in which case you had no option but to get a bit more slack on the wire so you could attach your crocodile clip through it.

My evidence on the whole was I think pretty good. I recorded my results twice, and they were pretty similar to the first set of results. The precision of the second wire was the best as I did not have any of the figures of voltage or amperage, smaller or greater than 3 tenths of my first reading.

Table Of Averages For The Three Wires

Analysis

As you can see that I only had two odd results, I cannot work out for sure the cause of the odd results but I guess that the wire may have heated up. But from the line of best fit I can estimate the resistance at 90 and 100 cm’s. The difference in resistance at 100 cm’ would have been 0.03 ohms. From my line of best fit I can estimate that the resistance in ohms will be 0.80 at 140 cm’s for wire 2 and 0.55 ohms for wire 1 therefore at 140 cm’s there would be a difference of 0.25 ohms. From this experiment I have understood that there is indeed a relationship between length and the resistance, and I do believe after testing different thickness of wire this theory is true for all wires.

From my graph on the last page, I have found out that the two wires I performed my experiment on had totally different resistance levels, I tested a thin, and a medium wire to check that the Wire 1, I think was the thickest wire, as had the least resistance in it. As the wire is thicker, it can allow the electrons to flow more freely, as there is a wide space for them to flow in freely. Wire 2 was to my prediction a bit thinner, I don’t recon it was that much thinner as the difference in resistance between wire 1 and wire 2 was only 0.051 ohms. If the electrons have to go through the atoms for a long period of length they are likely to slow down, therefore causing high resistance.

From he diagram above, I can visually explain why the resistance increases as the diameter of the wire is thinner. This diagram is trying to replicate a thin wire, the black are all the atoms and the blue is the electrons, the electrons are trying to navigate around the atoms to avoid bumping into them, but as the wire is full of these electrons, only a certain number of electron make it through the wire dodging the atoms, as the flow of electrons (current) is decreasing, more electrons are trying to push through the wire because there is still power coming from the power pack, but they are being held back by the atoms of the wire. So the thicker the wire is, the more freely the electrons can flow through the wire. So I have learned that a thicker and shorter wire makes for less resistance, and the thinner and longer wire makes for high resistance.

The pattern in my observation was that as the diameter of the wire increased the resistance decreased. I would have liked to check on some other material of wire to see that this property is not unique to this wire.

Evaluation

I think my results came out to be what I had predicted. One variable I felt I did not have that much control over was the wires in the circuit themselves, they are all different lengths and maybe also different thickness, this all means that the resistance could fluctuate every time I set the circuit up, and I had to add another wire to act as an extension wire to my circuit so that I could reach to the end the meter ruler. Another variable I noticed was the thickness of the wire, the thickness did make a difference to the resistance of the wire and I found out that any thickness of wire could increase resistance as the electrons increase the length of the wire that they travel through. My accuracy was good, I think that I have managed to get the results fairly close to my line of best fit; I have got two odd results and I think the wire just heated up a bit so that could be the reason for the odd results.

My plan was fairly reliable because I did not get that many odd results.

I think that the evidence is not enough for a firm conclusion as I would need to extend my enquiry further to see if the properties of different wires are similar, I would need to find out about the thickness of the different materials of wires to test if their resistance is similar or not, in addition to that I think if I were to extend my enquiry further I would need to have better control over the variables which I felt I did not have very good control over. I think that this enquiry has just scratched the surface of what would be a very interesting enquiry.