How does the length affect the amount of current flowing through a piece of wire?
How does the length affect the amount of current flowing
through a piece of wire?
Aim:
To see how the length of a piece of wire affects the current flowing through the wire.
Prediction:
I predict that the longer the wire the least amount of current flowing through the wire. So if the length increases then the resistance will also increase in proportion to the length and the current will decrease. I
think this because the longer the wire the more atoms and so the more likely the electrons are going to
collide with the atoms.
Scientific knowledge:
As a result of the structure of all conductive atoms, the outer electrons are able to move about freely even in a solid. When there is a potential difference across a conductive material all of the free electrons arrange themselves in lines moving in the same direction. This forms an electrical current. Resistance is encountered when the charged particles that make up the current collide with other fixed particles in the material. As the resistance of a material increases so too must the force required to drive the same amount of current. In fact resistance, in ohms(R) is equal to the electromotive force or potential difference, in volts (V) divided by the current, in amperes (I) - Ohm's law. As the length of the wire is increased the number of collisions the current carrying charged particles make with fixed particles also increases and therefore the value for the resistance of the wire becomes higher and the current becomes lower.
Preliminary Work:
We carried out a preliminary experiment to see the factors that could affect the experiment and also to see if we could improve any of the steps in the method. This showed that the wire was very weak if given more than 3 volts because the wire lets electricity flow faster and faster which then leads to the heat eventually breaking the wire. I found that if I decreased the voltage to a reading of 2 volts the wire stayed in tact enough to give a good reading and thereby giving better overall results.
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Preliminary Work:
We carried out a preliminary experiment to see the factors that could affect the experiment and also to see if we could improve any of the steps in the method. This showed that the wire was very weak if given more than 3 volts because the wire lets electricity flow faster and faster which then leads to the heat eventually breaking the wire. I found that if I decreased the voltage to a reading of 2 volts the wire stayed in tact enough to give a good reading and thereby giving better overall results.
Apparatus:
( 2 Variable Resistors
( Power pack
(Voltmeter
(Ammeter
(Wires
(Crocodile clips
(Ruler
Diagram:
Method:
(Connect a wire from the positive side of the power pack to two variable resistors.
(Then connect a wire from the resistors to the resistance wire using a crocodile clip.
(Connect the voltmeter in parallel to the resistance wire.
(Connect a wire from to resistance wire using a crocodile clip and then connect the wire to the ammeter.
(Then connect a wire from the Ammeter to the negative side of the power pack.
(Fix the voltage to 2 volts and measure the current when the resistance wire is 100cm long and record the results.
(Change the length of the resistance wire to 90cm, reset the voltage to 2 volts and record results.
Switch off the power and let it cool down.
(Change the length of the resistance wire to 80cm, reset the voltage to 2 volts and record results.
Switch off the power and let it cool down.
(Change the length of the resistance wire to 70cm, reset the voltage to 2 volts and record the results.
Switch off the power and let it cool down.
(Change the length of the resistance wire to 60cm, reset the voltage to 2 volts and record the results.
Switch off the power and let it cool down.
(Change the length of the resistance wire to 50cm, reset the voltage to 2 volts and record the results.
Switch off the power and let it cool down.
(Change the length of the resistance wire to 40cm, reset the voltage to 2 volts and record the results.
Switch off the power and let it cool down.
(Change the length of the resistance wire to 30cm, reset the voltage to 2 volts and record the results.
Switch off the power and let it cool down.
(Change the length of the resistance wire to 20cm, reset the voltage to 2 volts and record the results.
Switch off the power and let it cool down.
(Change the length of the resistance wire to 10cm, reset
the voltage to 2 volts and record the results.
Switch off the power and let it cool down.
(Use a voltmeter to measure voltage.
(Use an ammeter to measure current.
(Use a ruler to measure the wire.
Voltage
Length of resistance wire
Current
2
00
0.18
2
90
0.20
2
80
0.23
2
70
0.26
2
60
0.31
2
50
0.38
2
40
0.49
2
30
0.66
2
20
0.95
2
0
2.04
Results:
Voltage
Length of resistance wire
Current
2
00
0.18
2
90
0.21
2
80
0.26
2
70
0.28
2
60
0.32
2
50
0.38
2
40
0.49
2
30
0.66
2
20
0.95
2
0
2.02
Analysis:
I conclude that the longer the wire, the least current and the higher the resistance. This is because in a longer wire, there are more wire particles. Resistance is caused by electrons colliding with wire particles. Where there are more particles electrons are obviously more likely to have collisions, leading to a higher resistance and lower flow of current.
In a longer circuit, it is more of a struggle for electrons to get around the circuit without any collisions. There are lots more particles to avoid. Less electrons were able to get past at any one time in the wire, meaning that less current showed up on the ammeter. This means the longer the wire the higher resistance.
The wire with the highest resistance was the longest one - 100cm long. I predicted that the longer the wire the smaller the flow of current and the higher resistance, and this was the case. The reason for this is that there are not so many particles in a short wire. A low resistance translates as not many collisions, and therefore lower resistance. You could compare current to a high street. If you walk down one street and bump into a certain amount of people, in a street twice the length you are likely to bump into twice that certain amount of people. It is in this way that resistance works.
From my graphs you can see that it is a curve of best fit, this shows that as the length of the wire increases the flow of current decreases an so there is more resistance in a longer piece of wire.
On my second graph my results are slightly different but not much. I have one anomalous result this could have been caused by the temperature of the room increasing or because of the temperature of the wire because it would get hotter the longer it was left on for.
Evaluation:
I think that the test I used was fairly suitable, although not as much as I would have liked it to be, because I just used a crocodile clip to connect the wire at a certain length. Firstly, the crocodile clip is quite wide, and it is impossible to connect it at the exact length that you want. Secondly, the wire was not perfectly straight - it had several slight twists and bends in it, and this would have affected the accuracy of my results.
The only way I would be able to solve the problem of the bends and twists in the wire is to use a brand new piece of wire and look after it very carefully. I could solve the length problem by using a brand new piece of wire, which starts off at 1m in length, and I would cut it down to size for each result. This would make our observations closer to the exact length.
I had one anomalous result; it could have been because the temperature became too high, creating an extra variable to make the test unfair. If the temperature did get too high it would have increased the resistance and decreased the current. Similar to this idea, the wire could have had some impurities in it, varying the resistivity and increasing/decreasing the resistance. Any of the remaining three this because I have already used one in this experiment I chose length, factors affecting resistance could have been varied - temperature, resistivity and thickness, leading to unreliable readings. The other reason for an anomaly could simply be that we misread the voltmeter/ammeter.
To improve this experiment I could use an even wider range of results to increase the reliability of my results, or I could repeat the results more times.
Rebecca Day 10.1
