Now if I was to say double the length, then at the same time the resistance of the wire would also double. This would happen because; if the length is doubled then the number of atoms would also double. This would then result in a more number of collisions than before, and because there are more collisions this would slow down the electrons and increase the resistance of the wire.
Now the resistance depends on the length of the wire. If the length were increased than the resistance would increase, as well as the number of collisions, but, if the length decreased, then so would the resistance, which would then result in a low amount of collisions.
In order to maintain a fair test throughout the experiment, we must make sure we keep the following factors constant (same) at all times:
- Keep the voltage the same.
- Diameter of the wire must be the same.
- The atmosphere must be the same temperature.
- All equipment must be kept the same throughout the experiment.
- The edge of the crocodile clips should be measured by length at kept the same length at both sides.
- The type of metal.
In the following experiment we are going to change the length of the wire. First we will start off with a length of 5cm and then we will keep increasing it by 5cm until we finally reach 30cm.
We must be very careful that we do not cause any danger whilst performing this experiment. Here are some precautions you must take notice of:
- Do not carry out the experiment in wet areas or with wet hands.
- Make sure there are no exposed wires.
- Keep voltage the same so the wire will not burn.
- Do not touch the wire whilst power is on, as the wire will become hot.
- Be careful when cutting the wire, with scissors.
- Place a safety mat under the appliances.
- Make sure the mains is switched off, when removing wire from the crocodile clips.
The apparatus that we are going to be using are all listed below:
- Connecting Leads
- Crocodile Clips
- Nichrome wire 26 (SWG) Standard Wire Gage
- Voltmeter
- Ammeter
- Connecting Wires
- Ruler
- First I will set up the experiment as shown in the diagram above.
- Next I will get some wire, measure it to 5cm, then cut it with scissors and connect it to the crocodile clips.
- Switch on the power pack
- Now, I will record the reading from the ammeter and voltmeter, and write it in my table.
- I will repeat the experiment with lengths of 10, 15, 20, 25, 30cms of wire.
- I will perform the experiment twice, using the measurements above each time and write it in my table.
RESULTS NICHROME WIRE (26 SWG)
Resistance
5cm- 0.365
10cm- 0.613
15cm- 1.06
20cm- 1.310
25cm-1.7
30cm-1.984
I have also drawn a graph on the next page to show the best-fit line for my results in the table.
After carrying out the investigation I have reached to the conclusion that the longer the wire the higher the resistance. At this point I can clearly say that my prediction is correct because as you can see I stated that, if the length of the wire increases then the resistance of the Nichrome wire should also increase. Using my scientific knowledge I can say that resistance only occurs when electrons travelling through a wire collide with atoms in the wire. This depends on the length of the wire.
Now the length of a wire affects the resistance of a wire because, if the amount of atoms in the wire increases then this must mean that more collisions will take place, so there will be a higher resistance. So if the atoms increase than the length would increase, as well as the resistance, but if the atoms were to decrease, then so would the length and the resistance.
The main thing that affects the resistance is the number of collisions that take place between the electrons and the atoms inside of the wire. Now if we heat the wire there will be a larger number of atoms, so this means there will be a larger number of collisions, which will result in a higher resistance. The more collisions that take place, the higher the resistance will be, if there is a less number of collisions, then the lower the resistance.
So basically if the length of a wire contains a certain amount of atoms, then as we heat the wire and the length is increased, then the amount of atoms will increase resulting in a higher resistance because of the number of collisions. So the more the atoms, the more collisions and so the more collisions that occur, the higher the resistance will be.
As you can see on the previous page, I have drawn a line graph representing the voltage and current increase. I can see that the results I collected were quite accurate, but the graph did show some individual anomalous results. These anomalous results were indicated at points 0.365, 0.613, 1.06, 1.310, 1.7, and 1.984.
But on the other hand by, using all this scientific knowledge and skill I can clearly say that the results support my prediction and make up for a firm conclusion, but unfortunately for the 5 anomalous points there must be more accuracy made next time when reading the voltmeter and ammeter readings.
I think that the results I have collected in carrying out the experiment are quite accurate. This can be seen when we look at my graph, which shows a straight line, apart from the five anomalous points. It was difficult to draw the line at these points because; the length of the wire was longer at these points.
Although my graph is quite accurate and the results seem to be precise, there must have been some kind of mistake when I proceeded with the experiment, which has caused these points. The 5 points lie outside the line, but quite close.
On the other hand, in the experiment I acknowledged that if I increased the length of the wire than the wire became hotter and began to give off heat, this is why some of my anomalous points are located near the top of my graph. I think the reason why I have so many anomalous points is because,
- I did not measure the wire accurately enough and the wire was not stretched into a straight line so there were parts overlapping each other.
- The crocodile clips couldn’t be clipped on properly and kept on slipping and the distance they were kept were not measured accurately.
I should have made my measuring and the points noted above more accurate in order to obtain more accurate results and no anomalous points. In order to make these aspects more accurate I could have made a few modifications.
The modifications I would make would be to:
- Place the ruler under the wire to make more accurate measuring.
- Use pointers instead of crocodile clips, to make it more easy to clip it onto the wire and more accurate to measure the distance.
The graph I have drawn seems to be quite reliable because, even though there are five anomalous points. They are close to the graph and are just located outside the line of Best fit.
In the experiment I noticed that the ammeter and voltmeter flickered between a decimal point, so therefore, it could not present a precise final reading. So this means that the person noting down the readings could not be sure if his average result was correct.
During the experiment I did not keep a constant room temperature as this is not possible, therefore this could have made the wire become hotter more easily and more quickly. If this happened it would result in an unfair test, which would make my results not accurate enough. If future experiments I could have made changes by discovering a way to keep the surrounding temperature constant to make it a fair test.
All of this account further to my knowledge that my graph is quite reliable, changes could have been made if I was to repeat the experiment more times with the same lengths of wire.
I think that all the modifications I have noted above about improving my experiment and making the anomalous point more accurate, is quite high-quality information to be including in my evaluation and therefore these could be included if the experiment was to be a done another time.