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Choosing Wires to do Different Jobs in Electrical Engineering.

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Matthew Lawson 10 Bede

SC1 Investigation: Choosing Wires to do Different Jobs in Electrical Engineering.

Problem- I am going to try and find out how the resistance of the wire is affected as the length of the wire changes.

Variables- In this experiment I will be changing the length of the wire; this will be changed for each test that I make. I will use the same material for the wire, keep it the same thickness and at the same temperature as these may also effect the resistance of the wire if they are changed.

Prediction- I predict that as the length of the wire increases the resistance of the wire will also increase because the free electrons will have further to travel and will collide with more atoms and other free electrons in the wire. I also predict that input variable will be proportional to the output so if the input is doubled the output should also be doubled.




I will first set up a circuit like the one shown above including the Ampmeter and Voltmeter. I will choose one type of wire, which will always be of the same material and diameter, to act as a resister in the circuit. I will measure

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providing that the temperature also remains constant. Furthermore, the resistance of a metal increases as its temperature increases. This is because at higher temperatures, the particles of the conductor are moving around more quickly, thus increasing the likelihood of collisions with the free electrons.



  • Length of wire. *
  • Material of wire.
  • Width of wire.
  • Starting temperature of wire.


and thus the resistance of the wire. †

  • Voltage across wire.
  • Current in circuit.
  • Temperature of wire.

The variable marked with a * will be varied, the other input variables will be kept constant. The output variable marked with a † will be measured.


  • The longer the wire, the higher the resistance. This is because the longer the wire, the more times the free electrons will collide with other free electrons, the particles making up the metal, and any impurities in the metal. Therefore, more energy is going to be lost in these collisions (as heat).
  • Furthermore, doubling the length of the wire will result in double the resistance. This is because by doubling the length of the wire one is also doubling the collisions that will occur, thus doubling the amount of energy lost in these collisions.


The following circuit was constructed to perform the investigation:


The two dots (  ) represent the crocodile clips that were placed at the ends of the required length of wire.


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For a particular result, one or more of the connections could have been faulty, causing extra resistance at the connections. A solution to this would be to, before each experiment, connect the connections together without the wire in place and measure the resistance then. If it is higher than it should be then the connections could be cleaned. Whilst extremely unlikely, it is conceivable that the power supply was providing a different voltage for some of the results. This is unlikely to be a problem in this investigation but it might have been an issue had we used batteries instead.

NB:      If one were to assume that Ohm’s Law applies, then another possible explanation could be that at some points (more likely in the lower lengths), the wire was not allowed to cool completely so that the temperature was higher for that measurement. Whilst unlikely (due to the two sets of results), this would cause a higher resistance as explained previously. However, it is now known, after researching the metal alloy “constantan,” that the resistivity (the electrical resistance of a conductor of particular area and length) of this alloy is not affected by temperature. Therefore, in these experiments Ohm’s Law does not apply.

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