I have chosen to use constantan wire as from recent research I have found that it is not affected by heat from the outside of the wire. I have also found from doing a preliminary experiment that Constantan Wire gives a higher resistance than Nichrome Wire. I am using a thickness of 26 s.w.g because if the cross-sectional area increases, the resistance decreases but if the cross-sectional area decreases the resistance increases. This is because there is less room for the free electrons to collide and therefore friction from them creates heat and if the temperature increases, the resistance of the wire also increases. Therefore if I use the middle thickness I will get a more accurate result as it won’t be too thick but it won’t be too small.
Fair Test
I will make sure my experiment is fair by using constantan so that I know the temperature on the outside isn’t going to affect the resistance and so when I do the experiment I won’t need a water bath.
The thickness of the wire will be kept the same, as it would affect the result of resistance. It will affect it because as the cross-sectional area increases the resistance decreases because there is more space for the electrons to move around.
We have kept to having one type of wire – Constantan. This is because it has a higher resistance than nichrome and it isn’t affected by heat on the outside whereas nichrome is.
I have chosen to have a higher range because there won’t be much resistance to measure as if the length decreases so does the resistance.
I will use a power pack as the power from a battery can be lost, which would leave unfair results.
I have made the experiment safe by having a low voltage of 4V.
Prediction
The longer the wire, the higher the resistance. This is because the longer the wire, the more distance the free electrons have to move around and collide with each other. This will mean that more energy is going to be lost in these collisions as heat. The length of wire and resistance needs to be proportional because in a wire twice the length of another wire there would be twice the amount of atoms causing the resistance to double – Ohms Law. The movement of electrons through the metal structure causes resistance. As they move they bump into the metal ions. The metal ions are surrounded by a “cloud” or “sea” of electrons. Because of the structure of a metal they behave as conductors. The metal atoms release their outer electrons to form an electron cloud throughout the structure.
The power pack is supplying the energy to the electrons to make them move, so they are gaining kinetic energy. The collisions occur between the free moving electrons and the positive ions of the conductor that are vibrating about their mean position – but they are not free to move around the metal. This causes the electrons to lose kinetic energy whilst the ions vibrate more vigorously. The more energy that is spent forcing the electrons through, the greater the resistance of the material.
Results
Analysis
From my results I have found that the current decreased as the length increased and the voltage increases as the length increased. The resistance also increased as the length of the wire increased.
I have drawn a graph from the results of the average resistance. I was able to draw a straight line graph, a line of best fit – this is because of Ohms Law; the length of wire is shown to be directly proportional to the resistance – double the length and the resistance will double.
As I predicted the longer the wire, the greater the resistance, this is because the atoms of a metal are arranged in a regular pattern and are held in positions by strong forces. The outer electrons of the atoms have enough thermal energy to escape from the parent atoms and become free. By becoming free they have more room to collide into other free electrons, which causes friction which produces resistance. Therefore if the wire is longer the more friction is produced.
Evaluation
My results were fairly accurate as from my graph you can see that the majority of them fit into the line of best fit. There were about three anomalous results which could have been caused by having the range too long, which was started with a length too small. As from doing a preliminary experiment we found that using constantan wire with a length of 1 metre was fine with the power pack set to 4V but when we came to doing the final experiment we found that for the length of 10cm, 4V was too high and burnt the wire. Therefore we had to reduce the power pack to 2V and to make the experiment fair use that voltage for every length of wire.
If I was to do this experiment again I would increase the starting length of my wire so I can use a higher voltage on the power pack.
Although my results are not very accurate, they are quite reliable as we did the experiment three times for each length by taking the circuit all apart and setting it back up again each time.
Preliminary Experiment
I am doing a preliminary experiment because I will need to find out what is the best way to do the final experiment.
I need to find out;
- What type of wire to use
- The range of lengths
- The thickness of the wire
- What is better battery or power pack
Equipment
- Constantan Wire - 1 metre
- Nichrome Wire -1 metre
- Power Pack
- Digital Ammeter
- Digital Voltmeter
- Rheostat
- 3 x Crocodile Clips
- 3 x crocodile/plugs
- Metre Rule
We will only be testing one length for each wire just so we can see which type of wire gives the better resistance and if the thickness of the wire we have chosen is ok for the experiment.
Results
Conclusions
From my results I have found that the best type of wire to use is Constantan because it gives more resistance.
The thickness of the wire that we used was fine and as we had a choice of three; 24s.w.g, 26s.w.g and 32s.w.g so we chose the middle one as it won’t get too hot but it won’t be too thin. 24s.wg is the thickest wire.
The heat on the outside didn’t affect the constantan wire so by using this wire in my actual investigation I won’t need to use a water bath for the experiment and I get the best resistance.
The measurement of resistance will definitely be made by taking the results from the ammeter and the voltmeter in conjunction with Ohms law:
“The current flowing through a metal wire is proportional to the potential difference (P.D) across it (providing the temperature remains constant)”.
From doing this experiment I found that a rheostat wasn’t needed as we were repeating the readings from doing three experiments for each length of wire.
In the experiment, we took the length of wire as 1 metre and we found that this gave us a good reading and so we are going to use a large range of lengths – 10 cm to 100cm.