The aim of this investigation is to see how the length of a wire affects the resistance within it.
Deepak Chandi AT1
PLANNING
Aim:
The aim of this investigation is to see how the length of a wire affects the resistance within it.
Method:
The equipment that you would require for this experimentation is;
* Power pack
* Voltmeter
* Ammeter
* Normal wire
* Constantine wire
Here is the step-by-step process of the experiment;
. I will take the metre ruler with the wire attached to it and at lengths of 10,20,30,40 and 50cm we will connect the wire to the circuit.
2. I will make sure that everything in the circuit is working properly, e.g. that the power pack gives out exactly 6V.
3. I will set up the circuit.
4. I will take the reading of current from the ammeter.
5. I will use the reading I get to work out resistance, which the length of wire has.
6. I will repeat the experiment 5 times for each length of wire so that the overall average reading will be reliable.
To work out the resistance I will use the formula:
Resistance = Voltage / Current or R = V/I
Georg Simon Ohm first discovered this. (1787-1854). He was a German physicist, best known for his research on electrical currents. He was born in Erlangen and educated at the University of Erlangen. From 1833 to 1849, he was director of the Polytechnic Institute of Nuremberg, and from 1852 until his death, he was professor of experimental physics at the University of Munich. His formulation of the relationship between current, electromotive force, and resistance, known as Ohm's law, is the basic law of current flow. The unit of electrical resistance was named the ohm in his honor.
V
R x I
This triangle shows the relationship between voltage, current and resistance and how to work them out using the other two.
Variables:
The variable that I am going to change in this experiment is going to be the length of the Constantine wire. This means there is only one variable being changed. It is important that only one variable is changed because otherwise things can get complicated and that can cause confusion, which in turn could give you inaccurate readings, therefore you could not draw any conclusions from the experiments. You cannot draw any conclusions because they would be inaccurate. In addition, if you were changing more than one variable the aim of your investigation would change because you are measuring different things.
Here is a table to show the variables:
Constants
Variables
Circuit type and setup
Length of Constantine wire
Equipment used
Person measuring
Length of time given for wire to cool off.
Amount of voltage
Thickness of wire
It is important that the circuit type and setup remain the same because otherwise, the places where you measure resistance would change and in turn, the reading of resistance would change. Therefore, every time you took a reading it would have nothing to do with the next reading you took so you may as well not bother with the experimentation because you would have nothing valuable at the end of it.
It is important that the equipment used stays the same because no two pieces of equipment have the same readings and there is a percentage of error on each reading. It is better to keep the percentage of error the same all the way through rather than to have a different error each time. This will also go forward to guarantee a fair test.
It is important that the person measuring remains the same because everyone has different interpretations of readings. Therefore, it would be better to have the same interpretation all the way through because once ...
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It is important that the equipment used stays the same because no two pieces of equipment have the same readings and there is a percentage of error on each reading. It is better to keep the percentage of error the same all the way through rather than to have a different error each time. This will also go forward to guarantee a fair test.
It is important that the person measuring remains the same because everyone has different interpretations of readings. Therefore, it would be better to have the same interpretation all the way through because once again it's better to have the same margin of error all the way through.
It is important that the length of time allowed for the wire to cool remains the same all the way through because if the wire is at different temperatures, the amount of resistance within the wire would change accordingly.
It is important that the amount of voltage remains the same because this would affect the amount of resistance in the circuit. Remember, resistance is worked out by dividing voltage by current. If any of these two change, the resistance will change correspondingly. If the voltage also changes, we are introducing another experiment within this one. This in turn would give us inaccurate and useless results.
It is important that the thickness of the wire remains the same throughout because otherwise you are changing the amount of passage that the current has to pass through. This would change the amount of resistance accordingly leaving us with inconclusive results.
It is important that the circuit type and setup remain the same because otherwise, the places where you measure resistance would change and in turn, the reading of resistance would change. Therefore, every time you took a reading it would have nothing to do with the next reading you took so you may as well not bother with the experimentation because you would have nothing valuable at the end of it.
Fair Test:
In order to make this a fair test I will do the following:
* Only change one variable
* Use the same equipment
* Use the same person to take readings and measurements
* Keep the same thickness of wire
* Keep the same amount of voltage
* Keep the same type of wire (Constantine)
* Let the wire cool for the same period of time
Accuracy:
In order tom make this investigation as accurate as possible I will do the following:
* Use the same person to take readings and measurements
* Use the same equipment for each experiment
* Repeat each test 5 times
* Keep the same thickness of wire
* Keep the same amount of voltage
* Keep the same type of wire (Constantine)
* Let the wire cool for the same period of time
Reliability:
In order for this investigation to be reliable, I will repeat the experiment for each length of wire five times. Therefore, if one or two of the experiment results don't fit the general trend then you can discard those results and just keep the ones that fit the trend. Anything 20% off the average will be discarded.
Safety:
In order to make this a safe test, I will ensure that everyone involved will setup the circuit carefully and not let current pass through them or touch the Constantine wire while it is still hot.
Prediction:
My prediction is that as the length of the Constantine wire increases so will the amount of resistance in the wire. On a graph, this will be shown as a positive correlation. If the length of the wire is 10cm and the resistance is 20? then for 20cm the resistance should be 40?. This is because the length of wire and the time taken are directly proportional.
Longer Wire Has More Resistance
FIG. 1
+ -
FLOW OF ELECTRONS
FIG. 2
+ -
FLOW OF ELECTRONS
Fig. 1 is the shorter wire. It has less resistance because there isn't as much wire. The current only has to pass a small number of obstacles. Fig. 2 is the long wire. It has twice the amount of resistance because there is twice as much wire. The current has to pass twice as many obstacles. This also shows the two are proportional.
Resources:
www.aol.co.uk (homework help pages)
www.bbc.co.uk (revision pages, previous experiments and ask a teacher)
www.aol.com (homework help pages)
Diagram:
OBTAINING EVIDENCE
Results: HERE IS A TABLE TO SHOW MY RESULTS
TEST
WIRE (cm)
VOLTAGE
(V)
CURRENT
(Amps)
RESISTANCE
(R = V/I) (?)
AVERAGE
(R=V/I) (?)
0
0.20
.14
0.17
0.19
2
0
0.23
.13
0.20
3
0
0.21
.14
0.18
4
0
0.21
.14
0.18
5
0
0.21
.15
0.18
20
0.38
.14
0.33
0.31
2
20
0.40
.13
0.35
3
20
0.32
.14
0.28
4
20
0.32
.14
0.31
5
20
0.36
.13
0.32
30
0.46
.12
0.41
0.41
2
30
0.47
.12
0.42
3
30
0.47
.12
0.42
4
30
0.47
.12
0.42
5
30
0.44
.13
0.39
40
0.61
.11
0.55
0.55
2
40
0.62
.11
0.56
3
40
0.61
.11
0.55
4
40
0.59
.11
0.53
5
40
0.60
.11
0.54
50
0.72
.09
0.66
0.67
2
50
0.73
.09
0.67
3
50
0.70
.10
0.64
4
50
0.78
.10
0.71
5
50
0.70
.10
0.64
Observations:
Whilst the experimentation was taking place, I noted some of my observations:
* At 10cm wire does not heat up at all
* At 30cm wire heats a little with increased resistance
* At 50cm wire becomes quite hot even with little current passing through in short space of time
* 10cm wire has least resistance, 50cm wire has most resistance
ANALYSIS/CONCLUSION
Pattern of my results:
As you can see from the graphs I have drawn, a positive correlation has been shown just as I said I would get. From the line of best fit, you can see that as the wire length increases, so does resistance within it. As you can see from the triangles I have drawn on my graph the results are proportional. For every 10cm length of wire, the resistance increases by approximately 0.10?. This can be picked out at most points on my graph. The approximation would suggest that my results are not quite perfect.
The science that explains my experimentation is longer wire has more resistance. If there are x amount of particles within 10cm of wire, then there are 2x amount of particles in 20cm. If there are more particles there is more chance of them colliding with the electrons to slow them down. This also links in heavily with the Particle Collision Theory. The more particles there are, the more chance there is of them slowing down electrons by colliding with them.
Here is the order of resistance in each of the wires, starting with the lowest:
- 10cm
- 20cm
- 30cm
- 40cm
- 50cm
As expected, the 10cm wire had the least amount of resistance, and the 50cm wire had the most. This can once again be linked in with the science explained: The science that explains my experimentation is longer wire has more resistance. If there are x amount of particles within 10cm of wire, then there are 2x amount of particles in 20cm. If there are more particles there is more chance of them colliding with the electrons to slow them down. This also links in heavily with the Particle Collision Theory. The more particles there are, the more chance there is of them slowing down electrons by colliding with them.
The results are proportional, but they are not directly proportional. If they were directly proportional, the results wouldn't be the same distance apart, e.g. if 10cm = 100?, 20cm = 200?. They would double because the length doubles.
Results of my prediction:
The experimentation went exactly as I expected, except for the directly proportional theory. There was a positive correlation just as I expected. As the length of wire increased the amount of resistance in the wire increased. This is what I also predicted. With the exception of the part on proportion, my prediction was correct.
EVALUATING EVIDENCE
Improvements:
In order to improve this investigation there is one main area that needs to be improved. That is reliability. In school, it would be difficult to achieve this, because the equipment that is used isn't all that accurate. Another point that could be used is do the same test more times. This would give you a much better average. If you have more results, you have a larger base to backup your results.
Discussion of my results:
The following are just some points about my results: The differences between all the averages are more or less the same.
There weren't any erratic results anywhere. The results were constant.
The amount of current changes very slightly. As the length of wire increases, a small amount of current is lost.
When the thickness of the wire was 10 cm, the resistance was 0.19?. The resistance of the 20cm wire was 0.31?. This is a difference of 0.12?. When the thickness of the wire was 30 cm, the resistance was 0.41?. This is a difference of 0.10? from the 20cm wire. When the thickness of the wire was 40 cm, the resistance was 0.55?. This is a difference of 0.14? from the 30cm wire. When the thickness of the wire was 50 cm, the resistance was 0.67?. This is a difference of 0.12? from the 40cm wire. Just to show how consistent the differences were, here they are in a simple format:
0-20: 0.12?
20-30: 0.10?
30-40: 0.14?
40-50: 0.12?
These results boast an average difference of 0.12?. Seeing how consistent these results are, I would be able to predict the results of the next few results. For a thickness of 60cm, the resistance should be approx. 0.79?. For a thickness of 70cm, the resistance would be approx. 0.91?.
As you can see from the graphs I have drawn, a positive correlation has been shown just as I said I would get. From the line of best fit, you can see that as the wire length increases, so does resistance within it. As you can see from the triangles I have drawn on my graph the results are proportional. For every 10cm length of wire, the resistance increases by approximately 0.10?. This can be picked out at most points on my graph. The approximation would suggest that my results are not quite perfect. My graph also shows a general trend. As the wire length increases so does resistance within the wire. As expected, the 10cm wire had the least amount of resistance, and the 50cm wire had the most. This can once again be linked in with the science explained: The science that explains my experimentation is longer wire has more resistance. If there are x amount of particles within 10cm of wire, then there are 2x amount of particles in 20cm. If there are more particles there is more chance of them colliding with the electrons to slow them down. This also links in heavily with the Particle Collision Theory. The more particles there are, the more chance there is of them slowing down electrons by colliding with them.
Researching further experiments, I have come to the conclusion that my experiment is totally correct. The general trend that I can draw up is:
AS THE LENGTH OF WIRE INCREASES, THE RESISTANCE INCREASES IN THE SAME PROPORTION.
Looking at this general rule, I know I could predict the results for a similar experiment. This shows I have done what I initially set out to do.
