Investigating the Resistance of a Wire

Investigating the Resistance of a Wire
The Task: My coursework task is to review a section of a topic. We have been asked to investigate electrical resistance in a wire and the effect that changing one key factor has on resistance that the electrical current encounters. There are four possible factors that we might investigate: Length, cross-sectional area, temperature and the material used. I have chosen to explore the effect changing the wire length has on an amount of electrical resistance the wire encounters. The Aim: I am going to investigate how the electrical resistance of a wire changes in relationship to its length. The Prediction: I predict that, as length increases then the resistance will also increase in proportion to the length. The reason for my prediction is Ohms law which states: ?The potential difference (Voltage) between any two points in a conductor is directly proportional to the current flowing through it" - The Book of Ordinary Level Physics, V Î? L, V = I x R (R is the resistance, measured in ohms; L is the length, measured in cms; V is voltage, measured in volts; I is the current, measure in amperes) Resistance occurs in a wire because of the interaction of the electrical current with the wire atoms. In a piece of wire there is a number of atoms, these atoms come free moving electrons that flow between the atoms. These arrange them self?s in moving rows when voltage is fed into the circuit. This is known as an electrical current. When the electrically charged electrons, try and move through the atoms they collide with them. This in turn means the atoms loose some of their charge or slow down and create a resistance factor. Therefore the longer the wire, the greater the chance of the charged electrons colliding. I.E. If you double the length of the wire the number of atoms will also double, the electrons have twice the distance to travel resulting in twice the number of collisions, slowing the electrons down and increasing the resistance. Using Ohms law (above) we can see for a certain current, there will be a greater voltage across the wire if it has more resistance. So if we can increase resistance by increasing voltage and voltage is proportional to length, resistance must also be proportional to length (L). R Î? L (R is the resistance, measured in ohms; L is the length, measured in cms) In our circuit if we change the length the amount of collisions? should change directly proportional to it, if the temperature and cross-sectional area of the wire is kept constant. My graph backup my prediction as shows that length is proportional to the resistance: The Graph: Graph to show the relationship between Potential Difference (Voltage) and electrical Current [image] Apparatus Ø Power Source ? This will deliver the electric current to the circuit. Ø Ammeter ? This will measure the current in any part of the circuit Ø Voltmeter ? This will measure the amount of volts in the circuit. Ø Copper wire ? The copper wire I will study and do my experiment on. Ø Rheostat ? I am using this so I can take three different readings and come up with an average, to make my result and accurate as possible. Method 1. Set up circuit as shown in the following Diagram. [image][image][image][image][image]Crocodile [image]Clips [image][image]Copper wire [image] Oval: A Oval: A Ammeter Oval: V Voltmeter [image] [image] Oval: VRheostat [image] [image] [image] [image] Power source 2. Check if Circuit is Fair To check whether this is a fair circuit: (a)Tape copper 100cm wire to ruler. (b)Make sure copper wire is taught 3. Switch on the current 4.Take a reading from the ammeter and voltmeter 5. Take note of the readings 6. Turn power off 7. Repeat at 3 different levels on the Rheostat I will turn the power on; from there I will take reading from both the ammeter and voltmeter. Then I shall turn the power off. I will take three reading s, at three different levels on the rheostat. One at a long length, one in the middle, which will have been measured to ensure accuracy, and once from the short length. I will start this process at 100cm and from their I shall decrease in 10cms until I have reached a value of 10cm. From these values I will create averages for each length, and these averages I will record and turn into a chart. In this chart I will look to see if my prediction of there being a direct proportional change in the current and voltage of the copper wire. This experiment is not to dangerous but I am working with electricity so I still will have to be careful when handling the equipment e.g. not having wet hands. Also the wire we are working with will get hot quickly this is also a hazard and we will have to be careful. The wire heating up is also a point that might cause inaccuracy in our experiment. With more free electrons moving round the circuit, the longer the power is on the more collisions they are going to have with the atoms meaning, the atoms will heat up and will begin to move more vigorously. This heating effect will mean even more collisions due to the atoms movements. This means the resistance will increase, as the wire gets hot. To combat this we will attempt to leave the power on for only a limited time of under 5seconds. This will hopefully minimize the heating of the wire, and give us more accurate results. To give ourselves a fair test, we must keep everything in the circuit the same/ constant for all the measurements otherwise our results will not count as fair. We decided that a time of 5seconds should be given to take down the results, as we want all the length to have the same amounts of time for electricity to pass through them. We will keep the room temperature the same to the best extent that we can, as this might affect the temperature of the wire. Also we will keep all the rheostat measurements the same as this could lead to giving us inaccurate results. We will measure the 10cm intervals to the closest amount we can. All of these could lead to inaccurate results if we don?t try our best to keep them all fair. To improve the accuracy of my experiment I could also have tried some more preliminary experiments to give me the best chance of an accurate result. To learn about electricity and the similarities between current, voltage and resistance we did some experiments by looking at the resistance of a light bulb and also looking at resistors in series and parallel. To improve this we could have done some experiment looking at how different types and thickness of wire could change and give more accurate results. These might have helped when trying to get a wire that has a low conduction but still allows a good flow of electricity. Results Text Box: Lengths (cms) 1st Reading V I Ohms 2nd Reading V I Ohms 3rd Reading V I Ohms Average Reading Ohms 100 1.21 0.12 10.08 1.57 0.15 10.47 2.15 0.21 10.24 10.26 90 1.16 0.13 8.92 1.51 0.16 9.44 2.11 0.23 9.17 9.18 80 1.09 0.13 8.38 1.47 0.18 8.17 2.11 0.26 8.12 8.22 70 1.02 0.14 7.29 1.41 0.19 7.42 2.10 0.29 7.24 7.32 60 0.93 0.15 6.20 1.29 0.21 6.14 2.04 0.33 6.18 6.17 50 0.82 0.16 5.13 1.20 0.23 5.22 2.00 0.57 5.41 5.25 40 0.71 0.17 4.18 1.07 0.26 4012 1.97 0.48 4.10 4.13 30 0.56 0.18 3.11 0.89 0.29 3.07 1.85 0.60 3.08 3.09 20 0.47 0.20 2.35 0.71 0.31 2.29 1.69 0.79 2.14 2.26 10 0.24 0.22 1.09 0.42 0.38 1.11 1.37 1.28 1.07 1.09 [image] Conclusion As shown by my results, I can state that my prediction was correct. The resistance did change in proportion to the length. We can view this from the graph I have produced. As the length of the wire increased the higher the resistance. We can work out what the resistance of a wire should be from our results using Ohms Law I= V/R. Evaluation I believe I carried the experiment out very well. We came to the conclusion that the prediction we made was right. I have studied our results and have found that it linked in well with all of my preliminary thoughts on the resistance in the wire. I do not think we would need to repeat this experiment, unless we were going to attempt to get better set of results that were more accurate due to the equipment used. Accuracy was a prominent issue with this experiment. It is very hard to get the correct measurement without specialist equipment. This is one of the points I would look to improve if I had the chance to make my graph more accurate. Also I would look to improving methods of taking data down so we didn?t have the current running for half as long as the 5 seconds we allocated. This had a minor heating effect on the wire but I believe the constant switching had a large effect on the wire. I believe this caused the graph to look a little anomalous towards the shorter amounts of wire. This slight change I believe might be the cause of the constant switching. I would look to go back and some how improve the way of measuring the values. We started the measuring at the 100cm mark and went down in 10cm from there. The graph shows that at the 100cm point, the results are set out in a perfectly straight line but as we continue to look down the results, the line becomes less straight and beings to very lightly go of course. I believe this anomalous bending is due to the heating that is present in the wire so more free electrons start to collide with the atoms that with the heating are moving slightly more. I also think that the test that we carried out was a fair one with the equipment that we had. We made sure that everything was the same to best extent that we could. And we check all of the equipment twice to make sure we could get the best result possible. Their were no worries either on the safety side, as we made sure that every piece of equipment was in good working order and didn?t present any danger to the members in the group. I feel that I achieved my aim successfully and I can be very happy with my set of results.

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