I will calculate the resistance and see how the length affects the resistance. I am doing this because it was the easiest option with the equipment available and I feel it would be most fair with the best results.
Obviously, the temperature will remain the same as I will be keeping the voltage small (2V) so that the heating effect is small. Also, I won’t be changing the electricity but the electrons moving in the wire may heat it up causing the temperature to vary. I will monitor any changes in the ammeter and voltmeter as they determine what the resistance is
CIRCUIT DIAGRAM
This will give me the readings I need. The test wire will, obviously, be the wire I test. The variable power supply will power the circuit with the switch on to make a complete circuit.
The experiment can prove my prediction because I think the resistance will increase and if I am right the results will prove this. It will do so by myself taking a measurement of the ammeter and the voltmeter with every 5 centimetres of the test wire and then, using the equation, work out the resistance and compare the results with my prediction.
I did a trial experiment and I set up the equipment as displayed for my final experiment. I did this because it will help me in my final experiment; I know exactly what equipment to get how to set it up and it will be done at a quicker rate than if I was to go straight to my final. Not only that, but it has reassured me on my measurements I decided to do (5cm-50cm with 5cm difference between each.)
These are the results for my trial experiment:
In my trial experiment, it appears the voltmeter exceed 1.45 volts from the volt unit. The results and this conclusion show that there are only minor increases from 1 volt at what I originally began with and 1.45, the final result.
My results also showed me that my prediction was correct and that the resistance increases as the length of the test wire increases.
RESEARCH
Resistance is the property of any object or substance of resisting or opposing the flow of an electrical current. The quantity of resistance in an electric circuit determines the amount of current flowing in the circuit for any given voltage applied to the circuit. The unit of resistance is the ohm, the amount of resistance that limits the passage of current to one ampere when a voltage of one volt is applied to it. The standard abbreviation for electric resistance is R and the symbol for ohms in electric circuits is the Greek letter omega, Ω. The resistance of an object is determined by a property of the substance of which it is composed, known as the resistivity, and by the length and cross-sectional area of the object, and by the temperature. At a given temperature, the resistance is proportional to the object's resistivity and length, and inversely proportional to its cross-sectional area. Usually, a material's resistance increases with increases in temperature.
OBSERVING
I have ensured that I used the apparatus safely by double checking all connections are firmly in place, the volts on the volt unit are correct and that I have followed all instructions accurately.
Now that I have done my experiment, I know that I used sufficient ranges of values that give me clear and conclusive results. I believe repeating the measurements 10 times in each repeated test is quite enough for this experiment. It means that the average result will be very accurate.
These are the results for the final experiment with 3 measurements:
ANALYSING
My results have shown me that on averages, there is not much difference between the resistance results, for example: 2 out of the 3 averages are 6.89 and 6.29 which leaves the range to be just 0.60! So, in general, the averages work out to be roughly the same. Also, these results prove that my prediction was correct. They do because they show that as the length of wire increases as does the resistance. I got these results just by noting down the length of the wire at the time, noting down the volts each time, noted down the amps (current) and worked out the resistance on a calculator using the equation:
VOLTAGE
RESISTANCE=
CURRENT
I calculated the averages by adding all the ‘resistance’s’ up and dividing by however many measurements I took (in this case, 10). For example;
0.13
1.98
3.05
4.13
+ 5.78
6.95
9.33
11.00
12.00
- 14.50
10
6.89 (rounded)
Here are the three line graphs of the three measurements:
After looking at my line graph results with the line of best fit, I have concluded that the graphs seem fairly accurate with the odd exceptions of misleading dots. Those dots are probably out of place because the length of the wire was possibly not accurate or maybe the connections were out of place. I don’t think that is possible as I double-checked the connections before doing the experiment. Therefore, the length could not have been accurate.
Measurement one is the odd one of the three out; the line is steeper than measurements two and three. This suggests to me that maybe the length was shorter that what it was supposed to be at. For example, if the crocodile clip which links the circuit together was meant to be at 35cm but was at 33.5cm, this could dramatically affect the resistance. I actually think that it was more a case of the wire getting too hot as the dots are in a curve, too. But all three graphs go up in a curve just not as much as measurement one. Maybe the voltage should have been lower than 2V.
EVALUATION
From my analysis, it is obvious to me that my results were not completely accurate. However, they do give me an indication of what happens to the resistance when you increase the length of the test wire, which is the resistance increases as I predicted. So I now know that my results were useful but not entirely accurate. If they were accurate then I would be able to draw strong conclusions.
I have identified some anomalous results and them being are a few dots on either side of the line of best fit. I have put these down to the length of wire not being accurate. If I were to do the experiment again, I would definitely make sure the length was 100% accurate in order to bring the dots closer or on the line of best fit which would make my results more reliable. I have also recognised that the voltage in each measurement does not seem to increase as much as I expected and that in all four measurements, including my trial, it never went passed 1.45. But however, a solution to this would be to put the voltage up on the volt unit but the wire would get too hot and it was hot enough on 2V. So it is a good solution but I think the only solution. I don’t know whether the voltage not increasing as much as expected is what was meant to happen but it does not have seemed to affect my overall results. Other than that, I could not see anything else that went wrong with my results and experiment in general. What went right was that my circuit was complete, I got the results I needed and no accidents occurred throughout the experiment.
As an extension to this experiment I would see if the width of the wire affects the resistance. I would also predict that the width would affect the resistance and that the thicker the wire, the bigger the resistance. I think this because the thicker the wire means that there is more room for the current to flow and accelerate. Not only that but it lets more current in and therefore a higher resistance using the same equation:
VOLTAGE
RESISTANCE =
CURRENT
Then I would proceed with the experiment as I did in the ‘length against resistance’ experiment following the same instructions and using the same plan.
Kelly Duggan NDO physics coursework resistance 2/1/03
