I carried out a preliminary experiment to find out which apparatus would be best suited to find the resistance of Nichrome wire, to see the other factors that could affect the experiment and also to see if I could improve any of the steps in the method. I began by setting up two circuits, the first with a multimeter and the second with a power pack, I wanted to see which one would be more accurate for my investigation.
Using a multimeter is more accurate because it keeps the current going through the circuit low which keeps the temperature of the wire just about the same, this means if the wire is not heated and so the particles of atoms and electrons will not collide as frequently which therefore will not convert as much kinetic energy into heat which could affect the results. The multimeter will have the same current because of the fuse, the fuse only lets up to 0.
25A flow through any circuit, this is a low current so it will not give the wire a noticeable heating affect although there is very little temperature change, but it would not affect my investigation. If I used the power pack to find the resistance of the wire I would have to wait for the wire to cool down in between each reading for consistency, this is because as soon as the power pack is turned on the wire had already began to get hot so the heating affect works very quickly. I know this because I could feel or measure with a thermometer the difference in temperature of the wire to when it was not connected to the power pack.
If I did that it would not be as accurate as using the multimeter because the wire is hot. The resistance changes and makes it more difficult for the electrons to travel along the wire, this means the electrons are colliding more frequently. To test the resistance of the wire is the same throughout, I set up a circuit containing two leads, two crocodile clips, multimeter and Nichrome wire attached to a ruler. I then put the crocodile clips onto the wire at intervals of 100mm going from 0mm to 100mm all the way up to 1000mm.
This shows that the wire’s thickness could be the same throughout because the flow of electrons and atoms colliding is the same because it gives off the same resistance. I will use 100mm intervals because the meter ruler easily measures them, give a good range and give me a noticeable difference. If I only increased the distance by 50mm, that would give me results like, 0. 6ohms, 0. 7ohms and 0. 8ohms. If this happened in my real experiment that would not be very reliable because 0. 7 ohms could be anything from 0. 65ohms to 0. 74ohms and the 0.
8ohms result could be anything from 0. 75ohms to 0. 84ohms, this would mean that my results only had a 0. 01ohms increase so there would hardly be any noticeable change in resistance. Also in my preliminary experiment I used the multimeter, two crocodile clips and two leads to find the resistance of the leads and crocodile clips. It gave me a reading of 00. 3ohms. I needed to do this because it could affect my graph of results when the crocodile clips are at 0mm it would still give a reading of 00. 3ohms. I have also chosen to take 3 repeats at each length and then take an average.
I have chosen this so that if I have any anomalous results they will not show when I plot the averages on the graph. In my main experiment instead of using an ammeter and voltmeter I have chosen to use an multimeter, I have done this so that I am going to use the multimeter for my experiment because it is easier to use and it does not significantly heat the wire. The multimeter gives a direct measurement of resistance so therefore I think the multimeter will be more reliable and accurate. Method To do my experiment I will… 1) Set up the apparatus as shown in the diagram on page 1.
2) Attach the Nichrome wire to a 1000mm ruler with sellotape. (This will make my measuring accurate because I will be able to see where to put the crocodile clips and it will hold the wire in one place. ) I need to keep the wire straight because if it were bent the length of the wire would have increased affecting the investigation. 3) Start measuring the resistance by starting at 0mm-0mm and increase by 100mm each time e. g. 0mm-100mm. (I will do this because from my preliminary experiments I found that increasing the length by 100mm each time gave me a noticeable change in resistance).