Factors That I Could Have Chosen From
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Temperature - If the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. This causes more collisions between the electrons and the atoms as the atoms are moving into the path of the electrons. This increase in collisions means that there will be an increase in resistance.
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Material - The type of material will affect the amount of free electrons which are able to flow through the wire. The number of electrons depends on the amount of electrons in the outer energy shell of the atoms , so if there are more or larger atoms then there must be more electrons available. If the material has a high number of atoms there will be high number of electrons causing a lower resistance because of the increase in the number of electrons. Also if the atoms in the material are closely packed then the electrons will have more frequent collisions and therefore resistance will increase.
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Wire length - If the length of the wire is increased then the resistance will also increase as the electrons will have a longer distance to travel and so more collisions will occur. Due to this the length increase should be proportional to the resistance increase.
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Wire width - If the wires width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.
Method
For the experiment I set up a simple curcuit (see diagram) with a battery, ammeter, and voltmeter around the wire being tested. Crocidile clips will connect the wire. I will have 5 different lengths of wire to test, each of which will be tested twice, to get more accurate results.
I will then turn the power supply on and take readings from the ammeter and voltmeter and record them.
Resisitance is measured in omegas (Ω). The formula for this is:
Resistance (Ω) = Voltage (V) / Current (Amps)
e.g If voltage is 0.13 and current is 0.3 then 0.13 / 0.3 = 0.43 Ω
Equipment List
- Constatan wire
- Power Supply
- Connecting Wires
- Two Crocodile Clips
- Voltmeter
- Ammeter
Safety Precauitions:
This is not a very dangerous experiment but despite this you must always handle electricity with care, keep the current low, handle with dry hands etc.
Accuracy / Fair Test:
To keep this experiment as accurate as possible I need to make sure, firstly, that the length of the wire is measured precisely from the inside edge of the crocodile clips, making sure that the wire is straight when we do this. We must also make sure that the wire is straight when we conduct the experiment. If it is not, short circuits may occur may effect the resistance, also. The reading that we take of the voltage should be done fairly promptly after the circuit is connected. This is because as soon as a current is put through the wire it will get hotter and I want to test the wire when temperature is not affecting resistance, only length.
Results
Graph
Conclusion
From the graph I can see one very obvious trend, which is, as the length of the wire increases so does the resistance of it. Another, more significant thing is that it the increase is constant (pactically). I say this because the line is straight. I think that from my results I can safely say my prediction was right. The resistance did change in proportion to the length. This is because as the length of the wire increased the electrons that made up the current, had to travel through more of the fixed particles in the wire causing more collisions and therefore a higher resistance.
Evaluation
I feel that overall our results were quite accurate. This can be seen when I look at the graph, which shows a practically straight line with all of the points apart from one being very close to or on that line. The one point that was not that close to the line was a slight anomaly, but it was only slight and did not effect the final gradient of the graph.
Most errors in my experiment were encountered in the measuring of the wire. This is because it simply was not very practical to hold a piece of wire straight, whilst holding it next to a ruler and then trying to accurately fix crocodile clips to the right part on the wire. Also I do not feel that the crocodile clips were always fixed securely to the wire. This also meant that they were easy to move about on the wire changing the length of it. Errors rarely occurred in the setting of the current and the reading of the voltage.. Another example of this is the wire was never totally straight when I started the experiment, which may also, as said earlier on, effect the resistance of it.
