I shall look at various factors which can affect the resistance of a wire and investigate one of these in greater detail. I shall start off with theory on resistance and use it to make a prediction and then plan and carry out an experiment to obtain enough evidence to prove or disprove my prediction. From my data I shall plot graphs. I shall finish off by looking at errors and inaccuracies in my experiment and suggest improvements.TheoryAn electric current is the flow of electrons through a conductor. As these flow through the wire they encounter obstacle molecules, which are found in side the wire, and if they collide with these molecules they pass their kinetic energy to the obstacle molecules causing them to vibrate even faster than before leading to the heating up of the wire and the electrons loose their kinetic energy and slow down; thereby reducing the current flow.If the cross section (thickness) of a wire increases there will be more room for the electrons to flow around (up and down) and they will encounter more obstacle molecules which will slow the flow of electrons down so the resistance should decrease.Factors that could affect the resistance of a conductor are- the type of material used, the length of the wire, the thickness of the wire and the temperature of the wire. I shall investigate how the thickness effects the wire so I can see if my theory, that thicker wires will create more obstacle molecules which will obstruct the flow of electrons and slow the current down and reduce the resistance, is true or not.PredictionBased on Background theory I predict that as the thickness of the wire will increase the resistance will decrease and I will obtain the following graph:Preliminary workPreliminary work is needed to be carried out to determine the best voltage from the power pack to use; as if it was too high the wire would heat up and if the voltage was too less there would not be enough current running through. The best suitable material and thicknesses would need to be determined for the wire’s that are that are been tested, otherwise you would not get clear enough results. This work had already been carried out so we were given the best voltages to use and the 5 wires varying thicknesses.SafetyAs a power pack will be used, I need to be careful not to have any water near by. All books and bags will be kept away from the table. Metal jewelry on wrists or long necklaces and watches will be removed to avoid catching the equipment with the jewelry or watches. After every test the power pack will be switched off.EquipmentRather than batteries power packs will be used as they are high quality and provide fixed voltages. We will use digital voltmeters and ammeter for greater accuracy.Apparatus1 x Power Pack5 x Wires with different thickness1 x Digital Ammeter1 x Digital VoltmeterCrocodile ClipsSet up apparatusFair TestI shall ensure that this experiment is a fair test by ensuring that:* the wire to be tested all have the same length* all the wires are of the same material* all wires will have no bends* the voltage from the power pack will be kept the same* the same equipment will be used each time.Method1) Find the most suitable wires to use and the most suitable voltage from the powerpack to use2) Connect the wire that is to be tested to the circuit and switch on the power pack to volts3) Read off the readings from the ammeter and the voltmeter4) Repeat steps 2) and 3) for each wire 3 times to reduce experimental errors5) Once experiment is complete disconnect all equipment6) Work out the resistance from my readings off the ammeter and voltmeter7) Plot graphs and analyze my results.ResultsHere is a table of my results for each wire:1ST TEST 2ND TEST 3RD TESTVIRVIRVIRWIRE A (0.36)3.001.861.613.442.081.73.571.961.8WIRE B (0.32)3.301.402.43.671.642.23.821.542.5WIRE C (0.24)3.800.854.54.011.382.94.090.885.1WIRE D (0.16)4.200.518.24.350.538.24.330.449.8WIRE E (0.12)4.400.3114.14.490.3114.54.480.3014.9WIRE F (0.08)4.500.2022.54.550.2518.24.550.2121.7To calculate the resistance (R) I used the formula R=V/I, dividing the voltage (V) by the amps (I), so I could then plot a graph of the resistance against the thickness of a wire.AnalysisMy graph shows a curved line decreasing as the thickness greatens which show that there is not a sharp difference as predicted, as the resistance would decrease slowly.This as predicted clearly shows that as the thickness increases the resistance decreases because in thicker wires there will more room for the electrons to flow around and there are obstacle molecule to slow the flow of electrons down.EvaluationMy experiment worked successfully and gave me clear results to prove my prediction correct, prior to some anomalous results for example for a wire with the thickness of 0.24mm squared the resistance varied from 2.9 to 5.1 this large spread could have been due to several reasons, the wire may not of had enough time to return to its normal temperature and as a current in a wire will cause the wire to heat up, over heating would cause particles to vibrate more and increase the resistance which may be the reason that the 3rd test got the highest resistance of 5.1, or bends on the wire may of caused the second test to get the lowest resistance of 2.9. There were some other odd results as for the wire with 0.8mm squared varied from 18.2 to 22.5 which could have been caused by slight mistakes in my readings from the ammeter and voltmeter.I could have improved my experiment had I left the wires to cool down before taking the next set of results or made sure that there was no bending in the wire. I could have obtained more data by collecting data from other groups doing the same experiment and averaging them and I could have carried out the experiment with an even wider range of thicknesses, but overall I felt that experiment provided enough, reliable results to prove my prediction correct.


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