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To show how different factors affect the resistance of a wire and to what degree

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Planning I am going to carry out an investigation to show how different factors affect the resistance of a wire and to what degree. I know that resistance is volts over amps; this gives me an understanding of what resistance is. A complete circuit can be shown as a water model (see below) to show the different parts of a circuit, this will also help me to understand resistance. Factors The factors that might affect the resistance of a wire are: > Material > Cross-section area > Temperature* > Length Most of these are the main factors that affect the physical appearance of the wire so these are the obvious variables that are involved in my experiment. *However, I am excluding temperature in my experiments because the temperature range needed has to be extremely vast to be able to measure even the slightest change in resistance. To make the experiments a fair test the apparatus that I will be using has been precisely prepared to keep the dependent variable constant except the independent variable so the result can be accurately measured e.g. when I am testing the relationship between the length and the resistance, the cross-section area and the material of the wire will stay constant. I will do three different experiments measuring resistance with length, cross-section and material. Apparatus Method (a) For experiment (a) ...read more.


If this theory is applied to an electrical circuit it means that the resistance of the wire will be double if the wire is twice as long. I believe that the relationship between the cross-section area and the resistance will be proportional, however, it cannot be written as: Resistance proportional to cross-section area but as: Resistance proportional to 1 . cross-section area This is because the larger the cross-section area the smaller the resistance therefore the cross-section area has to be divided by 1. My reason for predicting this, again, came from the water model. When the pipe is halved in cross-section area, the friction between the same amounts of water going through the pipe will double as the water molecules are pushed into a much thinner pipe, which means the molecules are under higher pressure. When this theory is applied to an electrical circuit it means when the cross-section area is halved the resistance is twice as much. If my predictions are correct, the graph for a proportional relationship should have a straight line going through the origin. Obtaining Evidence Results (a) Resistance (?) Length (cm) 2.2 10 4.1 20 6.0 30 8.0 40 10.0 50 12.0 60 13.9 70 15.9 80 17.8 90 19.19 100 (b) Resistance (?) Cross-section area (mm�) 3.3 0.2025 4.0 0.1600 6.3 0.1024 7.5 0.0784 10.5 0.0625 15.5 0.0400 25.0 0.0256 (c) ...read more.


in a water bath using water resistant apparatus. This would have given me even more accurate results. I do not know how precise the rods were for experiments (a) and (b), however, I am sure they are much more accurate rods which I could have used to carry out the experiments in order to gain truer results. I found the conclusion was easy to foresee, as it was a simple investigation, also the water model helped me greatly to forecast the results. Therefore when the results matched my hypothesis I was certain that they were accurate. I had some slightly anomalous results in experiment (a); when the length was doubled the resistance was slightly under what it should have been. This could have been due to the fact that an extra centimetre of constantan was needed to be bolted to the wood, however this would have increased the resistance, not decrease it. Another factor could have been that the screw that was used to fix the constantan was made of iron; iron has a lower resistance than constantan so this is probably the reason the resistance was slightly lower than what it should have been. I would carry out experiments to see how temperature would affect the resistance of the wire, also I would like to find out if the shape of the wire's cross-section would have any effect on the resistance. I could extend experiment (a) further to see if the relationship would still be proportional if different materials are used. ?? ?? ?? ?? Sean Fang 9DW ...read more.

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