Investigating how the length of a wire Effects resistance.
Lee Powell
Investigating how the length of a wire Effects resistance.
Planning
Aim: I am going to investigate how the length of a wire affects resistance.
Scientific Research: Current is a flow of charged particles, usually through a circuit, in all dry conductors, the flow is of electrons and so are negatively charged.
Resistance is in electricity, it is a property of an electric circuit or part of a circuit that transforms electric energy into heat energy in opposing electric current. Resistance involves collisions of the current-carrying charged particles with fixed particles that make up the structure of the conductors. Resistance is often considered as localised in such devices as lamps, heaters, and resistors, although it is characteristic of every part of a circuit, including connecting wires and electric transmission lines.
Resistance has a relationship with length, the longer the length of the wire the greater the resistance. This is because there are more positively charged particles to get in the way of and collide with the electrons. This means there are more particles to get past so the resistance is increased.
There are four factors that can affect resistance, varying cross sectional area of the wire, different material for wire, temperature of wire, and the one I am interested, in varying length of the wire. Varying cross sectional area effects resistance because if the wire is thicker it allows the electrons to flow more freely, so the resistance is then lower. The temperature affects resistance because as the metal's temperature rises its constituent atoms vibrate more vigorously. This increases the amount of interaction between the atoms and the current carrying electrons. The flow of electrons is impeded, increasing the resistance. The length of a wire affects resistance because the longer the wire, the more particles there are to get in the way of the flowing electrons. We need to keep the other three factors constant so that the test is fair.
The relationship between voltage, current and resistance is expressed in Ohm's law.
Ohm's law is: R=V?I
RESISTANCE(?)=VOLTAGE(V)?CURRENT(A)
Ohm's Law states that: the current flowing through a metal wire is proportional to the potential difference across it (providing that the temperature remains the same).
I found some of this informatin from a website:
www.homework-high.com
Prediction: From my research I can now predict:
. If I increase the length the resistance will increase, this is because the length and resistance are directly proportional.
2. a) if I increase the length by ...
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The relationship between voltage, current and resistance is expressed in Ohm's law.
Ohm's law is: R=V?I
RESISTANCE(?)=VOLTAGE(V)?CURRENT(A)
Ohm's Law states that: the current flowing through a metal wire is proportional to the potential difference across it (providing that the temperature remains the same).
I found some of this informatin from a website:
www.homework-high.com
Prediction: From my research I can now predict:
. If I increase the length the resistance will increase, this is because the length and resistance are directly proportional.
2. a) if I increase the length by 10cm the resistance will increase by about 0.5?.
b) if I double the length the resistance should double.
3. if the voltage doubles the current doubles as well.
Safety: -do not touch the test wire, as it maybe hot. I will turn the power off at regular intervals to let it cool down.
-make sure there is no water, or you don't have wet hands, because it is still electricity.
Equipment List:
* 1.2m length of Constantan 28SWG (standard wire gauge).
* power pack.
* ammeter.
* voltmeter.
* crocodile clips.
* metre ruler.
* wires.
* variable resistor.
Apparatus Diagram:
Method:
. collect equipment.
2. set up equipment, as shown in apparatus diagram.
3. use metre ruler to measure 50cm of wire, and attach crocodile clips.
4. switch on, use variable resistor to get 1v on voltmeter.
5. record reading from ammeter, then switch off to let the wire cool down.
6. repeat steps 4 and 5 for 2V, 3V, 4V and 5V.
7. repeat steps 4, 5, and 6 for lengths 60cm, 70cm, 80cm, 90cm, and 100cm.
Fair Testing:
* To make sure the test was a fair one, we had to make sure the wire was the correct length, measured very accuratly.
* We had to try and keep the temperature as constant as possible, this would mean allowing the wire to cool down after each test.
Results:
length=50cm
voltage(V)
current(A)
Resistance(?)
0.41
2.44
2
0.83
2.41
3
.24
2.42
4
.65
2.42
5
2.1
2.39
average resistance=2.42?
length=60cm
0.35
2.86
2
0.7
2.86
3
.05
2.86
4
.39
2.88
5
.73
2.89
average resistance=2.87?
length=70cm
0.28
3.57
2
0.57
3.51
3
0.85
3.53
4
.13
3.54
5
.4
3.57
average resistance=3.66?
length=80cm
0.27
3.7
2
0.53
3.77
3
0.81
3.7
4
.08
3.7
5
.35
3.7
average resistance=3.71?
lenght=90cm
0.24
4.17
2
0.47
4.26
3
0.71
4.23
4
0.95
4.21
5
.19
4.2
average resistance=4.21?
length=100cm
0.22
4.55
2
0.44
4.55
3
0.64
4.69
4
0.86
4.65
5
.07
4.67
average resistance=4.62?
Analysing
Having completed my experiments, I have found that resistance increases when the length of wire increases.
From my graphs I can see the following patterns:
. if I increase the length by 10cm the resistance increases by 0.5?.
2. I have also seen that if I double the length, the resistance nearly doubles, length and resistance are directly proportional, so we should have let the wire cool down again.
3. using my voltage against current graph, I have found a line that proves Ohm's law, it is my 60cm graph.
If I double the voltage from 1V to 2V, the current doubles from 0.35A to 0.7V.
Conclusion: I conclude that increasing the length increases the resistance, this is because, when the wire is made longer, there are more metal atoms to get in the way of the flowing electrons, as it is put in my scientific research.
I predicted that:
. if I increase the length the resistance will increase, this is because length and resistance are directly proportional.
2. a) if I increase the length by 10cm the resistance will increase by about 0.5?.
b)if I double the length the resistance should double.
3. if the voltage doubles the current will double as well, this is proving Ohm's Law.
My results prove this, although my results are not completely accurate, that is mailnly due to human error, I believe that if we had done everything absoloutley perfectly then our results would have been very accurate.
Evaluating
My experimental procedure was good, it was easy to follow and got good, accurate results that I expected.
Most of the points plotted on my graph are close to the line of best fit. This means our experiment was conducted well.
The experiment just about followed Ohm's Law, the reason it didn't quite follow Ohm's Law absolutely is because Ohm's Law is only correct if the temperature remains the same.
My experiment followed expected results as can be seen by using my prediction, results tables and graphs.
I have a few anomalous results, the most obvious one is on the "A graph to show average resistance against length" it is at 70cm, most of the other results are very close to the lines drawn on the graphs so must be quite accurate. The reason I have these anomalous results is due to change in temperature while completing the experiment.
I believe that I have gathered enough evidence to support my conclusion, I repeated the experiment five times for each different length to make sure of this, and get an accurate average resistance.
Improvements:
* Some improvements I could have made are to have kept the temperature constant, and made shure of this, by keeping the length of wire in a water bath at a constant temperature.
* I could also have made the experimient contain more values, e.g. go from 1-10V instead of 1-5V this would mean I would get more results, and the average result would have been more accurate, as the anomolies wouldn't affect the results as much.
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