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Find out how the length of a wire affects its resistance.

Extracts from this document...


Hawa Mohamed-11x2


   Aim: the aim for this course work is to find out how a length of a wire affects its resistance

Variables: the factors that can affect the resistance of a wire are…..

  • Length of the wire
  • Temperature of the wire
  • Diameter and thickness of the wire
  • Material of the wire

Out of all these factors I’m only going to test the length of a wire using constantan wire and I will compare the length of the wire and its resistance

Prediction:I predict that, the longer the length of the wire, the higher its resistance. My reason for saying this is because resistance is caused in metals by free electrons bumping into ions, and for this reason they slow down in the wire. There fore more energy is lost in these collisions as heat. If the length of the wire is doubled so will the electrons that era bumping and they are bumping to the ions as twice, and there fore there will be more resistance to movement of electrons, so resistance is proportional to the length. In other words, as the length of the wire increases, so will the resistance and the number of electrons that are passing through the wire. But the current will decrease because current is the flow of electrons


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     Safety:  while I’m doing this investigationI will consider the     safety elements…….

  • ensure that I don’t touch the wire while its hot
  • I will also choose a low voltage so that it won’t over heat.
  • Further more I will not try a length of less than 10cm, this is also helped me avoid over heating.
  • I will also make sure that the area I’m doing my experiment is clean and no bags and anything else around.
  • I will be wearing safety goggles to protect my eyes from the heat.
  • I will also turn the power pack off each I’m doing the readings, because it will over heat.

    Fair testing: to make it fair testing, I will consider the factors that affect the resistance of wire are constant. I will be using the same piece of wire through out the investigation, and the same equipment, as it will decrease the chance of errors in my result.

Key factors: the length of the wire and the area of the wire are the factors that will vary. The key factors that I will change as a result are the length of the wire. The dependent variable is the resistance. However I will keep the

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     Evaluation: over all my result is quite accurate due to the fact that nearly the entire points bar sits on the line of best fit except at 100cm which is 18.2 ohms. The reason is because at 90cm the resistance was 17.7 ohms, but at 100cm it goes up high at 18.2 ohms. I think that happened because I didn’t turn the power pack off when I was reading the result for 90cm, and it got hot, so when I changed the crocodiles to 100cm, it was already hot and the voltage and current was high. If I could improve this investigation, I would let the wire cool down completely, so the temperature wasn’t high enough for that measurement, causing the resistance to be high. But after I done some research I found out that metal alloy like constantan is not affected by temperature. Therefor in this experiment ohms law does not apply. The investigation would also be more accurate if I used digital ammeter or sensors. My method was accurate because I repeated the investigation each time I got it wrong improving it more and making sure that I don’t make the same mistake.

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