Physics Coursework – Carbon Track Experiment Aim: To investigate if the resistance of a carbon track is proportional to its length and width. Introduction: Carbon has interesting properties and this is why I am investigating it as it is a very important element in electronics. It is a semi-conductor, which is why carbon is very interesting, which means that it behaves like an insulator when cold, but when warm it becomes poor conductors. Carbon is a form of graphite, which I will be using to investigate.
Graphite is unusual because it is a non-metal which conducts and is the only non-metal pure element that conducts electricity which makes it useful in electronic circuits. Theory: Resistance (considered in this experiment) is the slowing of a current through the carbon track. This means that the carbon track is a conductor. A conductor is an element which allows electricity or heat through their electrons. The more free electrons elements have, the more that element can conduct. The electricity gives the free electrons a charge and so they begin to move randomly and crash into other free electrons.
This happens all along the length of the conductor and so the electrons begin to move from the negative connection to the positive connection (this happens because electrons are negatively charged). Resistance is caused by these free charged electrons crashing into fixed particles (nuclei and protons), other free electrons and particles. As results to these collisions, heat is giving off causing these free charged electrons to lose some of their energy. This loss of energy causes the electrons to slow down and so the flow decreases.
All readings will be measured in ohms: “a steady current flowing through a metallic conductor is directly proportional to the resistance between the ends of the conductor, provided that the temperature and other physical conditions are kept constant. ” Although ohms law applies to metallic elements, I feel that as carbon conducts electricity, this should be included in ohms law. This is why I shall use ohms law in this experiment. This is to show that the current flowing through the carbon track remains constant. This is because the more current put through the carbon track the more heat is produced.
The rise in temperature as a large effect on the resistance quite dramatically. This is because the higher the temperature, the higher the resistance, because as the material gets hotter the fixed particles begin to vibrate very quickly increasing the chances that they will collide with free electrons. Hypothesis I think that the resistance of a carbon track will increase in proportion to its length. I think this because the more electrons the current has to pass through, the more collisions they make and so the higher the resistance. I predict that the graph would look like this:
My theory helps back up my prediction; the more current, the more quickly the free charged electrons would move randomly, causing more heat (less energy) which means that there would be more electricity. For the width, I predict that as the width increases, the resistance decreases. I think this because as the width does increase, the free charged electrons have more carbon ions to collide with, and so the resistance would decrease. I predict that the graph would start with a low resistance with the largest width, and then decrease until it starts to level out.
For the resistance against the reciprocal of width I think that the resistance will rise when the reciprocal of the width increases. I think that the graph would look like this. Fair testing To make this experiment a fair test I will only have independent variable and one dependent variable for each series of results. I will test how the length and width affect the resistance, but only one at a team. In other words, when investigating how length affects the resistance, the width would be kept constant and visa versa.
This is because otherwise I will not be able to extinguish whether there was a change in resistance due to the change of length or width. I must not the metal whilst I am doing the test as I also conduct electricity because I am moist and so I must avoid contact with the metal. I must keep one experiment on the same carbon track and not use a new carbon track whilst in a middle of a set of results. This is because if a new carbon track was used, in the middle of a set of results, then the thickness (height) of the carbon track would be different. Doing these would make this investigation a fair test.