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Plan
In this investigation I am going to look at how the resistance of a piece of copper wire differs depending on its length. In stages of 10cm. For this I will need
· Power source To supply the electricity.
· Variable resistor To control the voltage flowing across it.
Cheap Custom Essays on Resistance of a Wire
· Voltmeter used to measure the potential difference between two points.
· Ammeter used for measuring amount of current in a circuit.
· Crocodile clips to alter the length of the copper wire without actually cutting it.
And obviously copper wire and leads to connect the instruments together.
There are certain aspects to the investigation that could affect the results, these are known as variables. Some of the variables that are relevant to my investigation are
· Length
· Thickness
· Temperature of wire
· Material used
· Voltage passing through
To make the data I collect valid I must maintain control of these variables and keep them the same through out. They way I will maintain them are; Length, if I say the piece of wire is 0cm I must make sure it is exactly 0cm. Thickness, If I used more then one piece of copper wire there is a great chance the thickness would differ. So to prevent this I will only use one piece.
Temperature of wire, when the wire heats up it causes more resistance. Resistance is caused when these electrons flowing towards the positive terminal collide into ions and they lose energy, to keep the wire at a low temperature I will use a variable resistor. Material used, I am going to use a copper wire throughout. Voltage, the more voltage the more resistance, I must try to keep the voltage at roughly the same level, for this I will have to place my trust into the makers of the power-packs we use. If the dial is set to 6 volts then I must trust it is actually 6v (or neigh on) and I mustn't adjust the dial throughout the experiment. If I do not maintain these variables my conclusion may come out false, as my results were not taken under the same condition.
I think that the longer the wire the more resistance this is because metals conduct electricity as the atoms in them do not hold on to their electrons very well, and create free electrons. As I said before resistance is caused when these electrons flowing towards the positive terminal collide into ions and they lose energy. So if we double the length of a wire, the number of atoms in the wire doubles, so the number of collisions double, so twice the amount of energy is required. Resistance is measured in Ohms. Resistance is a measure of how much the current is slowed down. Therefore the smaller the current, the bigger the resistance.
R= V / I Is an expression of Ohms Law
Resistance = Voltage / Electric current
1. Take a power source and connect a lead to one black port and one red port. See fig.1
. Connect the Variable resistor to the red lead. See fig
. Connect a lead to the open port on the variable resistor (see fig a) (correct way to connect a variable resistor)
Attach a crocodile clip to the end of the lead and clip it onto the bronze wire at 0cm. See fig
4. Connect another lead with a crocodile clip a 100cm to the copper wire and plug the other end into an ammeter join the black lead from the power source to the ammeter as well. See fig 4
5. Now we must loop the voltmeter around the copper wire. To do this we must plug a lead in each of the back ports connected to the copper wire. Then plug the lose ends into a voltmeter. See fig 5
The initial work I did was actually doing the rough trials at different voltages and noting the results down. For the final results I will take readings from the wire in stages of 10cm. I will take the reading three times for each length, then add the three readings up and divide by three to give me an average reading for that specific length. I will also keep the voltage the same for all three trials.
Observations
To work out the resistance, I implicated ohms law.
Test one
Length of wire (cm) Potential difference (Volts) Electric current (amps) Resistance (ohms)
10 0.50 0.81 0.6
0 0.80 0.76 1.05
0 1.0 0.71 1.55
40 1.5 0.66 .05
50 1.55 0.6 .50
60 1.7 0.55 .15
70 1.86 0.5 .51
80 .00 0.51 .
0 .17 0.4 4.4
100 .0 0.47 4.8
Test two
Length of wire (cm) Potential difference (volts) Electric current (amps) Resistance (ohms)
10 0.50 0.8 0.61
0 0.85 0.76 1.1
0 1.01 0.7 1.8
40 1.5 0.68 1.84
50 1.55 0.64 .8
60 1.7 0.60 .80
70 1.86 0.57 .6
80 .00 0.5 .7
0 .17 0.51 4.7
100 .0 0.48 4.7
Test three
Length on wire (cm) Potential difference (volts) Electric current (amps) Resistance (ohms)
10 0.4 0.8 0.5
0 0.85 0.77 1.10
0 1.06 0.7 1.47
40 1.8 0.66 1.4
50 1.48 0.64 .1
60 1.70 0.60 .8
70 1.8 0.56 .8
80 .0 0.54 .74
0 . 0.51 4.5
100 .0 0.48 4.7
To work out the resistance we must apply Ohms law
R= V / I Is an expression of Ohms Law
Resistance = Voltage / Electric current. So in test one, when the wire is 0cm long the volts (p-d) is 1.0, the electric current (I) is 0.71. So, 1.0/0.71 = Resistance, 1.0/0.71= 1.55(reoccurring) the same answer in my table. Take test two, 70cm. The volts is 1.86 and the electric current (I) is 0.57, 1.86/0.57= .6. Take test three, 50cm. The volts is 1.48 and the electric current (I) is 0.64, 1.48/0.64= .1.
Test average
Length of wire (cm) Resistance (ohms)
10 0.61
0 1.0
0 1.46
40 1.4
50 .6
60 .
70 .7
80 .8
0 4.5
100 4.8
I worked out a test average so that I could draw a graph of average data from the results, if I didn't average my results I would have had to draw three graphs.
Analysis.
The longer the wire became the more resistance created. When the wire was 10cm long the resistance was 0.61, when it was 0cm long it was 1.0. This shows us the resistance nearly doubled as the length doubled. From the length 0cm to the length 100cm the resistance increased by 0.48 ohms. I also notices that further on in my average results table as the wire length increased by 10 the resistance increased by 0.5-0.55 ohms. My results support my prediction 'I think that the longer the wire the more resistance.'
This happened because of more free electrons flying about inside the wire.
I have drawn this diagram to explain clearer.
Cross section of copper wire with electricity passing through.
Free electron Ion
Inside, the Ions are stationary, but the electrons move about. If they didn't collide with the Ions no resistance would be made. If this is still unclear then look at it like this; a man (electron) has to run through a maze (Copper wire) without hitting no walls (stationary ions) to escape (create no resistance). My prediction was the longer the wire the more resistance and my results supported this evidence. At first I though that instead of going up in stages of 10cm maybe 5cm would be better, then I realised that it didn't matter if I took two readings or two-hundred readings my answer would still be the same but the two-hundred reading one would be more detailed. Therefore I think that my results are valid proof that the longer the piece of copper wire the more resistance, but they are only valid to someone doing exactly the same experiment as me, because if someone was investigating the resistance of a piece of wire, but failed to maintain a constant temperature then I am almost certain out results would differ greatly.
Evaluation
I feel my method gave good results; I can only find three pieces of anomalous data and even those do not greatly differ from the others, they are the second, third and fourth results from my second test under the potential difference column. The only explanation I can think of is faulty power packs, maybe at that point masses of people also turned on their power packs causing a brief flux in the power. Overall I believe that my method work as to plan, unless all of my data is incorrect because I did the test wrong, but comparing my work to others it seems in order.
The only other reason I can think of as to why the results may contain anomalous data is because of variables I didn't maintain; Diameter, at some point during the piece of wire it is probable the diameter increased, this may make my results differ from others, amount of time electricity was passed through the wire prior to the reading or maybe not maintaining a constant exterior temperature. I could measure the diameter of the wire and see if the wire greatly differed in diameter at any points to prevent getting more anomalous piece of data in the future. Or maybe use a stopwatch to see how long each reading session takes.
In my investigation I used copper wire, so my final result would be that resistance increases with length in copper wire, of course this may not be the case in other materials such as; Iron, steel or gold. If I investigated the resistance with these materials my answer could be more generally defied. I could also control the amount of time the electric current was passed through before a reading was taken, maybe the longer the electric current is passed the less resistance is made, because the electrons find the shortest possible route with the least collisions.
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