During this experiment I need to be aware of the safety element of it and therefore prevent any possible hazards before they can occur. As there is electricity involved I will ensure that the experiment is set up away from any water or other aquatic conductors. I will make sure that the power supply does not exceed 3V so as not to have a dangerous current flowing through it. I will also wear safety goggles to protect my eyes as there is a possibility of the wires snapping. There is also a chance of the wire becoming very hot but to prevent this happening I will put in a switch so that the power is not constantly on.
I will also use a variable resistor that I will use to get different values for the voltage and current for each wire. This will allow me to collect more results and have a sufficient amount to plot the relevant graphs.
To make sure that this experiment is a fair test I will use the same length of wire for all of my repetitions so that I can compare the results fairly. I will also keep the temperature in the room as constant as possible as I know that the temperature can affect the resistance in a wire. The power supply will not exceed 3V as this a large supply may also cause the temperature inside then wire rise thus affecting the resistance. I will also use a switch so that the power will not be running when I do not require it to.
Results
I will now display the results that I found. This will be shown in tables of results for each SWG followed by a graph of voltage verses Current to determine the resistance of that particular wire. Firstly however, I will show my results for varying the length of the wire. This will be shown in a table and then a graph plotting the length against the resistance.
I will also show the graphs comparing resistance to cross sectional area as well as resistance verses 1/area.
Now that I have found the resistance of the wire for each SWG, I will put all of the data found into a table so work out the resistivity of the wire.
Analysis of results
I will firstly analyse the first part of my experiment which was to see how the length of the wire affected the resistance. Looking at the graph that I have drawn plotting resistance against length, you can clearly see that the length is proportional to the resistance. As the length of the wire increases, so does the resistance. The graph shows that this obeys Ohm’s law as it is a linear line and that it passes through the origin. This is generally what I expected to find for this part of my experiment. The resistance in the wire should increase with length as the electrons have a longer distance to travel through the wire.
The rest of my results of tables and graphs are to determine the resistance of each wire so that I am able to find the resistivity of nichrome wire. The graphs I have plotted are Voltage against Current so that I am able to read off the gradient of each graph as it will be the resistance. The graphs also show that the voltage is proportional to the resistance and obeys Ohm’s law as they are all linear graphs and should pass through the origin had the results been more accurate.
Once I found the resistance I was able to then calculate the Resistivity using the formulas already stated above. Looking at my final values of resistivity I was pleased to see that 3 of them were almost identical, (SWG 18, 26 and 30), but was curious as to why the other two were of similar values but different to the other three.
My other two graphs show the resistance against area and resistance against 1/area. The first graph showed that as the cross sectional area of the wire increased so the resistance decreased. This is due to the fact that as the area increases there is a larger space for the electrons to pass through and so the resistance of them passing through would decrease.
Evaluation of experiment
I believe that this experiment went well and am pleased with the results that I recorded. I managed to use the time given affectively to collect a great deal of results to perform the calculations to enough detail to get an accurate reading for the resistivity. Looking at my results however I seem to have two separate readings of resistivity. In this experiment there should not be very many factors that would affect my results. There may however have been some resistance lost internally in the wires used in the experiment. I doubt that the internal resistance lost in the wires would account to the two different readings and so there must be another reason for the result. This may be due to the wires that I used being slightly different materials. 3 of them seem to be the same leaving the other 2 to a different material.
Another factor that could have affected my results could have been faulty equipment such as the voltmeter and ammeter may have not been very accurate or could have been telling me different values altogether although I am confident that this was the case due to the shape of my graphs drawn. This is due to my scientific knowledge that the Voltage and current are proportional to each other as shown in my graphs.
If I was to repeat this experiment I would do use the same method as I did in this one as I believe it to be the most effective way in determining the resistivity of a wire with the equipment available for me to use.