A conductor = current through the conductor
Which in short can be written as
V
R=
I
Variables-
The main factor of the whole experiment is the wire that we use to test the resistance. The wire will be in use the hole time through out the experiment. Beginning from 100cm and ending at 10cm. The only other factor that will affect the wire is the temperature, the reason being because I have worked with it if the electricity is left for a long time on. Then the wire will start to melt or if it is on a higher electricity level from the power pack then the wire will actually burn.
Prediction-
I predict that the longer the length of the wire the higher the resistance because, the longer the wire the more ions it will have, so theoretically there are more opportunities for the free moving electrons to collide with the ion. Which reduces its speed so to this the resistance increases also predict that the length of wire would be directly proportional to the resistance. So if you increase the length by two the resistance would also increase by two times. I predicted this because from my past learning and the information I have gathered tells me that this is true.
(GCSE physics by Duncan) clearly states the resistance of a wire is proportional to its length (quadrupling the length quadruples the resistance)
And (lets revise GCSE science) also suggests, the length of wire is proportional to its resistance
Apparatus-
Ruler-100cm long with the wire attached to it with tape.
Voltmeter –this was connected parallel to the wire
Power pack –the supply of energy was put to two volts
Ammeter –this was connected from the positive side of the power pack to the positive of the ammeter with a lead because this is the best way to get an accurate reading.
Leads –this connected all the equipment
Crocodile clips –this was used to connect the leads to the metal wire to let a current pass through.
Variable resistor- if reading of voltmeter beyond range adjusted.
Method-
My circuit was set up like this:
+ Variable resistor
Power pack
Voltmeter
Ammeter
+
+
100 cm
Ruler
Test wire
In this investigation a simple circuit will be set up to read the voltage and current when the length of the wire changes. The circuit should be set up as above. The length will range from 10cm - 100cm (1m) with intervals of 10cm. Moving the crocodile clip across the wire on a ruler will change the length of the wire. If I am doing the experiment rite then I should be able to spot a pattern straight away. This way I would be able to see if the experiment is going ok. Of the pattern does not show up then the experiment that is being carried out is wrong. The wire that I will be using should be the same one through out the whole experiment. That is why it was a good idea to do a preliminary to see the maximum electricity that the wire can take before it starts to melt. If the wire melts or burns then the whole experiment will have to be started again.
Fair testing-
To make this experiment a fair test I have to make sure I keep the other factors, which affect its resistance, constant throughout the experiment by keeping the wire and its width the same. And to test the wire at room temperature. However I cannot stop the wire getting hot as it is out of my control because the ions and electrons have to collide in order for me to test and in return heat energy is produced making the metal wire hot, which may affect its resistance. However I can try to minimise this error by turning the circuit off as soon as I get the reading. So that there would be less collisions as possible between the electrons and ions I could also make this a fair test by taking each reading three times then take the average to calculate the resistance. So that the numbers I get after each calculation would be fair as possible and sensible to my conclusion. The power pack will first be
Preliminary-
The problems that I saw in the preliminary investigation were as follows; voltage on power use, eliminating links on to the wire, using a rheostat to get precise readings on the ammeter and the voltmeter.
Table of results-
Conclusion-
The graph gives a reasonable straight line and it shows a positive correlation between the length of the wire and its resistance. And the second graph clearly shows that an increase in the length of wire results in an increase in the resistance, which tells us that the resistance is directly proportional to the length
Just as I predicted this could be explained to the fact the free moving electrons colliding with the ions in the metal wire cause that resistance. And the longer the wire the more collisions there will be. And due to this we can say that
R=KL
Which means that the resistance stays constant to the length
Evaluation-
Generally I am pleased with my results as they formed a straight line on the graph, though some of the points were not in favour of the line. However I can explain this, when the electrons and ions collide with each other heat is produced and to this result the metal wire gets hot and temperature is one of the main factors which effect the resistance of the resistance wire. Because this would give the electrons more energy so it could collide with more ions in one go. That is why my results may not have been very accurate. Another possible reason could be due to the fluctuation of the pointer on the ammeter and so I had to catch the reading very quickly. And again due to this I may not have got very accurate results. Overall I’m very confident with my results and I believe I have made a sensible conclusion that the resistance is directly proportional to the length with my results even though I made slight errors the conclusion agreed with my prediction.
The possible improvements that I could have made with my results could have been to use digital meters or to use an ammeter that did not fluctuate and could have used another resistor to make sure that the right amount of current went through the circuit. I could have also used an ammeter and a voltmeter that would allow me to have a wider range of readings so I could test the resistance of the wire in 5cm length so I could explain my conclusion in more detail.