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Investigation into the resistance of wires.

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William Pearson                                                                       12/02/03

Investigation into the resistance of wires

Background Information

Resistance of electrical current is all based around ohm’s law. R=V/I This is:  resistance = potential difference / the current.

I know that there are several different factors that affect the flow of electrons along a wire. These are: Cross-sectional area

Length of wire

Conductive material and

Surrounding temperature

I will now explain each in more detail.

Cross-sectional area

        The larger the cross-sectional area of the wire the less resistance it has.  This is due to the larger spaces between atoms through out the wire allowing electrons to have a smaller amount of collisions with fixed particles therefore having a lower resistance.image22.png

Length of wire

        When the length of the wire changes so does the resistance.  The longer the wire is the more chances the electrons have to collide with a fixed atom reducing the flow.  Therefore; the longer the wire the greater resistance.  


The Temperature

        The temperature of the wire and its surroundings has an affect because the higher the temperature the more energy the atoms in the wire have, they will move faster and through greater distances.  This leads to greater number of collisions with static particles producing a high resistance.


Conductive material

        The material the wire is made of plays a great part in resisting the flow of electrons.

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1 length of wire (constantan 0.31) over 1000mm

1 voltmeter

1 ammeter

1 rheostat (variable resister)

1 clamp stand

1 set of weights

2 crocodile clips

4 cells (batteries)

6 connecting wires


        I want to find out the relationship between the length of the wire and the resistance of it.


  1. Gather all equipment needed
  2. Place out in correct order and assemble circuit
  3. Connect the crocodile clips to the wire 200mm apart
  4. Set the rheostat so that the voltmeter reads 3 V.
  5. Read the ammeter and record the result.
  6. Reset the crocodile clips to 400mm apart
  7. Reset the rheostat so the voltmeter reads 3V
  8. Again record the result.
  9. Repeat this process 3 times for each length (200mm, 400mm, 600mm, 800mm, 1000mm)


        To make sure that the experiment is accurate I need to insure that I read the ammeter and voltmeter exactly and make sure that the 2 crocodile clips are correctly placed at the stated distance.

Fair test

To keep the experiment fair I need to eliminate all the other variables apart from the one I am going to investigate.  To do this I will ensure I use the same wire so that the material and the cross-sectional area are the same.  Also I will carry out the experiment in approximately the same environment so moisture and temperature are the same each time to eliminate those factors affecting the results.  Plus, I will only have the current flowing when I need to make readings so it would not heat up.


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  1. Firstly I would use a more sensitive ammeter and voltmeter so that the reading I took could be more accurate. Also I would use digital ,metres so they would be easier to read. Therefore improving my results.
  2. Secondly I would work out the resistance of all the components in the circuit so that I could take them into consideration when doing calculations.
  3. Thirdly I would use better quality crocodile clips to make sure that the connection between them and the wire was strong.   Also this would prevent them from slipping.
  4. I would keep a very high resistance in the circuit so to keep the current low.

After studying the results I have found that they are not suitable to form a solid conclusion on as they stand.  Even though the experiment was taken out to a good standard there are still improvements that need to be made to get a reliable set of results so that I can form a conclusion.  I would improve the experiments and apparatus in the ways stated above.

If I were to extend my investigations I would have to use a wider range of readings so I could gain enough information to put together a reliable and accurate set of results to produce a firm specific conclusion.  Secondly I would use a better standard of equipment so that I will eliminate this factor that could affect my results.  Also I could investigate other factors that will affect the resistance, such as temperature, diameter and the material of the wire.


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