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Investigating how the length of a wire affects the resistance.

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Claire Bartlett 11KA (Set 1)

Investigating how the length of a wire affects the resistance.


        The aim of this investigation is to find out how the length of a wire affects the resistance of it.


        I predict that the longer the piece of wire, the greater the resistance will be. I think this because of the theory of free moving electrons being resisted by the atoms in the wire. There for in a longer piece of wire, there would be more atoms for the electrons to collide with and so the resistance would be greater.

        I also predict that the relationship between the wire length and the resistance it creates would be directly proportional. This is because in a wire twice the length of another wire of the same material, thickness and in the same temperature would ha double the amount of atoms causing twice the amount of collisions causing twice the amount of resistance.

Predictive graph


        The variables in this investigation are: -

  • The length of the wire this is the only variable that I will be changing
  • The temperature of the wire. I will try and keep this constant by only using on cell in my experiment
  • The material of the wire. I will keep this constant by using the same wire throughout my investigation
  • The thickness of the wire. I will keep this constant by using the same wire throughout my investigation.

Fair Test

To ensure that this investigation is a fair test and that my results will be as accurate and reliable as I can make them I will have to make shore that only one variable in the investigation changes and all the others will stay constant. To achieve this I will: -

  • Pull the wire tight against the ruler and tape it in place securely so that I can measure the wire accurately.
  • The same equipment all the way through the investigation so that I do not introduce variables by changing equipment.
  • Only using one cell so that the wire only heats up minimally, because electricity creates heat and if the wire heats up it will change the resistance in the wire because it will mean that the atoms in the wire have more energy to collide with the free moving electrons. Due to the fact I am investigating wire length and its affect on resistance I want the wire to heat up as little as possible.
  • I will use the same wire throughout so I don’t change the material or the thickness of the wire.
  • I will repeat results where necessary.
...read more.


To change the length of the wire I moved a chisel edge across the wire on the ruler. The chisel edge I used is shown below and it was connected into the circuit with the wire attached.
  • Record the voltage and the current for each 10cm interval
  • Then work out the resistance by using the formula:

V = R


        Where V = voltage, I = current and R = resistance.

  • Plot a graph to show the
...read more.



This investigation was quite easy to carry out and I think that my results were more accurate that I first thought that they would be. This can be seen in the graph where by all of the points are on or very close to the line of best fit. This shows that the inaccuracy of my results was minimal.

Dew to the nature of electrical experiments I was expecting a larger level of inaccuracy mainly dew to human error. For example not getting a good connection with the chisel edge, reading the voltmeters and amp meters wrong, and errors with calculations of the resistance. Also inaccuracy could have occurred with the equipment for example having an old cell so it was running down. Other things that could have caused inaccurate results are not measuring each length accurately dew to the accuracy level of the meter ruler and accuracy levels of the amp meter and voltmeter.

If I decided to carry on my investigation I could investigate how wire thickness or how the temperature of a wire affected the resistance.

...read more.

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