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To Investigate How the Resistance of a Constantan Wire Changes When Length Changes.

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Introduction

Physics coursework plan Aim- to investigate how the resistance of a constantan wire changes when length changes. Key factors- * Thickness of wire: if the wire is thin, the electrons are forced to travel through a smaller area. This results in them colliding more often so they give up more of their energy to surrounding particles. * Temperature: resistance increases as the temperature increases. This is because atoms in the wire are oscillating faster. When an electron collides with an atom, it loses energy. If the wire cools, resistance will decrease. * Length of wire: the longer the wire, the larger the resistance. More particles are in the way, so electrons find it hard to flow. Also, a longer wire means the electricity is forced to travel further. Electrons bang into each other so resistance increases. More energy is used. * Conducting material of the wire: if the metal is a good conductor, there is less resistance due to the fact that more current can flow. If the material isn't a good conductor, less current flows through, so there is a larger resistance. Another way in which the conducting material of a wire affects the resistance is that some metals have a lot of electrons that are mobile (able to move). In this situation, there is less resistance. It is more difficult for current to flow through when there are few electrons able to move. ...read more.

Middle

- Make sure the total length of wire is exactly 1m. - Record the current and voltage accurately, using the correct units. - Always place the crocodile clips on the right measurement. - Before you start the experiment, test the devices being used. If any are faulty, change them. - Leave the power pack set at the same voltage for the whole of the experiment. - The surrounding room temperature must be kept, otherwise the particles in the wire will move faster (if the temperature increases). Therefore, this will have an effect on the resistance. - The wire along the metre ruler must be straight and exactly 1m long. Bends in the wire may affect the resistance. - The reading of the voltage should be taken promptly after the circuit is connected. This because as soon as a current is put through the wire, it will get hotter. I want to test the constantan wire when heat is affecting it the least. Safety- - Do not set the power pack voltage to more than 2V. This is a safety hazard. - If you smell burning, promptly switch off the power pack from the mains. - Make sure that when the power pack is switched on, the near by taps are switched off. If there is any water spilt near by the sockets or surrounding areas, wipe it before you start the experiment. - Make sure the power pack cable or the conducting wires aren't frayed. Results table- Length (cm) ...read more.

Conclusion

It is difficult to get an accurate reading of length by eye, as the wire may not be completely straight. If I were to do this experiment again, I cold use a more accurate voltmeter, as this was when the anomalous result occurred. Another factor that perhaps reduced the degree of accuracy was the connection of crocodile clips. They may not have always been connected to the constantan wire securely. This meant they could have been free to move, altering the length of wire and therefore accuracy of readings (voltage and current). I can prove that my experiment was successful because of the graph I drew. It showed length of wire against resistance. I don't think that by doing any more results in my experiment would improve the accuracy at all. I took three readings each of voltage and current and also worked out an average, which I used to work out the resistance. The only way to make the results more accurate is to use a different method. Perhaps I could use a metal bar in place of the wire. This way, I could still investigate the length of wire affecting resistance, but more accurately. A disadvantage of this would be that the attachment of the crocodile clips would be less secure depending on the width and thickness of the wire. If I had the chance to do the experiment again, I would investigate other factors. Examples of these are temperature, voltage or current. I would see how these additional factors affect the resistance. Observations Results table- ...read more.

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