# Resistance of a Wire Experiment

I will be investigating how varying the length of a wire can effect the resistance that it has. The diagram below shows how my experiment will be set up and the apparatus I will use: Variable Power Pack [image] [image] [image] [image] Before carrying out the experiment I have to decide which wire to use out of three available types, I require the one with the lowest percentage error between the maximum and minimum voltage so that in my main investigation I will have much more accurate results. The three available types are: ? Nichrome ? Copper ? Constantine I will be doing a preliminary test to decide which wire I shall use. The parameters of this test are set out below ? The Variable Power-Pack will be reset to 0.10 amps, to make sure the wire is cool and the resistance in each wire is at its normal level and also so that the 3 experiments are more even and fair. ? I will do the test three times for each wire to give far more accurate readings ? The current will always stay at 0.10 so that it remains a fair test ? The length and diameter of the wire will remain constant for all three wires to keep it fair. I have displayed the results from my preliminary experiment in the table shown below: Wire Length Min Voltage Max Voltage Difference Copper 100cm 19.3MV 26.4MV 7.1MV Nichrome 100cm 1.79V 1.82V 0.03V Constantine 100cm 0.817V 0.846V 0.029V The reason I have recorded the maximum and minimum values reached is because I want the wire with the least fluctuation in voltageAlthough the table shows the Constantine wire to have the lowest difference with only 0.029V between the maximum and minimum readings. I?ve decided that Nichrome is actually better as the difference (0.03) is a much lower percentage of the average voltage for the Nichrome (1.805) than the Constantine difference (0.029) is of its average voltage (0.8315). Going of this information I have decided that doing my main experiment with the Nichrome wire will give much more accurate readings and much better results. Now that I have finished my preliminary investigation to decide the best type of wire, I can begin my main investigation. In this investigation the only factor that I will vary is the length of wire. To make sure it is a fair test I will keep the current the same (- 0.1 amps) and I will keep the diameter and the type of wire the same (Nichrome) I am going to use ten different lengths of wire equally spaced between zero and one hundred centimetres. During the tests I?ll measure the voltage three times across each of the different lengths of wire, to prove that the results are consistent. Between each individual test I will turn the power pack off, leaving the wire to cool down because the resistance in a wire increases if it gets hot. Then I will then turn the power pack back on and reset the current to 0.1 amps. My prediction is that as the length of wire increases so will the resistance. This is because metals are made of positive nuclei and negative electrons. As the electrons move they have a chance of colliding with the positive nuclei. The collisions are what cause the resistance and if an electron is forced to travel a longer distance it has less chance of avoiding all the nuclei meaning there is more chance of resistance. I should actually be able to calculate the resistances I will get using this formula R= rl r = 100 × 10 -6 W cm A R= 100 × 10-6 × 100 P x 0.0142 = 16.24 W This means that the resistance for 100cm of wire should be roughly 16.24 Ohms I have entered the results from my final investigation into the table shown on below. I then graphed it to try and find a trend. The graph shows that there is a clear growth in resistance as the length of wire was increased. Wire length Voltage on test 1 Voltage on test 2 Voltage on test 3 average ohms 10 0.19 0.19 0.19 0.19 1.9 20 0.4 0.4 0.4 0.40 4.0 30 0.6 0.61 0.6 0.60 6.0 40 0.8 0.81 0.81 0.81 8.1 50 1.01 1.01 0.98 1.00 10.0 60 1.19 1.2 1.19 1.19 11.9 70 1.38 1.39 1.38 1.38 13.8 80 1.62 1.63 1.6 1.62 16.2 90 1.75 1.74 1.74 1.74 17.4 100 1.97 1.97 1.98 1.97 19.7 The graph is shown below: [image] The results given are slightly higher than what I originally predicted but this could be due to one of many reasons such as letting the wire get too hot or Dents in the wire, which would reduce the cross section area and once again reduce the chance of electrons getting past the nuclei increasing resistance. I believe that my results are accurate as I took the test 3 times with each length and then took the average although heat or dents in the wire could still affect results. There are a few ways I could have made my experiment more accurate, for example if I put the wire in an oil bath. The oil would disperse the heat from the wire keeping it cool, and this would lower the resistance. Also if I took the tests in the reverse order. 100 ? 10cm then the dents would not have been there which would have reduced the resistance. Overall though I believe my experiment was successful because the results increased with the length of the wire, which was what should have happened.

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