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To find how the resistance of a piece of wire depends on its length.

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Resistance Coursework

Aim: To find how the resistance of a piece of wire depends on its length.

Prediction: I predict that the length of the wire will effect the resistance by the longer it gets the resistance will increase.  I feel this will happen because the further apart the crocodile clips, in the circuit, then the further the electrons have to travel so the resistance will increase.  We did a preliminary experiment to find out the resistance of different wires.  In the experiment we kept the same length (60cm) and the resistances varied by a decimal point or stayed the same.  So from this I can predict that if you increase the length of the wire then the resistance will increase also.


  1. Collect and set up apparatus like in the diagram above.

  2. Decide on length of wire between crocodile clips.  I decided on 10.0, 20.0, 30.0, 40.0,50.0, 60.0,70.0, 80.0, 90.0, 100.0, 110.0, 120.0 and 130.0cms.
  3. Take length set up circuit and turn on to take readings from Voltmeter and ammeter.
  4. With same length move to another position on wire and take readings.
  5. Move to third position on wire with same length and take readings.
  6. Now calculate average resistance using formula:                     R (resistance) = V (potential Difference) over I (amps)
  7. Take next length and follow instructions 3 to 6 for the rest of the lengths.

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Accuracy: I can make it accurate by measuring the length of the wire to the nearest millimeter.  I can also use digital meters so that I have the closest measurement I can get.  I could also use a stopwatch so that I could take the readings after the same amount of time.

Processing Results: In the preliminary experiment I had three different wires with three different types of thickness.  I had three tables to go with the wires and I had to calculate the average resistance of the three wires.  To do this I used the mean by adding the results of one of the wires (which I did three times, but in different positions) and divided by three.  This gave me an average for each wire and I intend to do this with the different lengths of this experiment.

Conclusion: The resistance increased with length just as I predicted in my prediction.  This is because the further the length of the wire then the further the electrons have to jump. For example, if the length was of the wire was 30.0cm (to the nearest millimeter) and the resistance is 6.2Ω, then the resistance of the wire will have increased if the wire was at 120.0cm, which has a resistance of 13.

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I feel that my results were very reliable but not very accurate.  The first four set of averages I had were basically the same and varied from a couple of decimal points which are reliable but not accurate.  The results of the rest of the points were more accurate just not as accurate as they could be, if you look at the graph (the red ink line), but I think they were very reliable.  The most they varied from was on the last reading which was one whole Ω from 13.8Ω to 14.8Ω.

I feel the conclusion I came to was the best I, personally, could have come to.  I also feel that I could have had a better and more accurate conclusion if I had extended my experiment into lengths of over two meters and up.  To make it even more accurate I could have tried using different metals and different types of thickness for example, using constanton with SWG (Standard Wire Gage) 24, 28 or even 36 to get a wider range of results.  After doing that I could have declared that,

“Resistance rises with length”.

I could say that now but I don’t know that if I get to a certain length it might stop rising and just stay the same from there onwards.

Shaun Slater 11y

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