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Resistance occurs when electrons travelling along the wire collide with atoms in the wire.

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Resistance occurs when electrons travelling along the wire collide with atoms in the wire. These collisions slow down the flow of electrons causing resistance. Resistance is a measure of how hard it is to move the electrons through the wire. Resistance is measured in Ohms. The greater the resistance the greater voltage is needed to push a current through the wire.

Electrons carry energy around the circuit. There are positive ions, which are fixed, but vibrating, while the negative electrons are free to move. If the electrons collide with the ions energy is transferred and the ions vibrate with larger amplitude.

The word equation for resistance is:

In a resistor the current is proportional to the potential difference (Ohms Law.) This means the resistance is constant at all potential differences. We can increase the resistance by increasing the potential difference or decreasing the current. Potential difference is the energy transferred per charge. If the electrons transfer more energy the potential difference will increase.

Current is the charge that flows past a point per second so the fewer electrons the smaller the current.

Resistance is high in plastics (insulators) as there are no free electrons but in copper (conductor) there is a low resistance as there are many free electrons.


In this investigation I aim to investigate the resistance of six wires with different diameters but the same lengths. I also aim to investigate if different factors increase or decrease the resistance.

These factors are:

  • Wire length – the longer the wire the more distance the electrons have to travel so the more collisions with ions will occur. The length of the wire is proportional to the resistance.
  • Wire width – the resistance will decrease if the wire width is increased as the electrons have more space through which to travel so more electrons can flow. This means there will be a larger current meaning smaller resistance.
  • Temperature – if the wire is heated the ions start to vibrate with greater amplitude due to an increase in energy. The electrons will collide into ions more frequently causing the resistance to increase.
  • Material – the type of material that the wire is made up of will affect the amount of free electrons, which are able to flow through the wire. The number of electrons is dependent on the amount of electrons in the outer energy shell of the atoms, which make up the material. The greater number of atoms or larger atoms will result in more free electrons and, therefore, higher resistance. Also if the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase.


I think that as the size of the wire increases the resistance of the wire will decrease. I believe this as every atom has about one free electron and the greater the size of the wire, the more atoms the wire has. The free electron is important as it moves from a place where there are too many electrons to a place lacking electrons. As a thicker wire has more spaces it is easier for the electrons to move, but in a thinner wire there is less space it is harder for the electrons to move we call this resistance.




Pre Test

I decided to do a pre-test because I thought that it would aid me in completing the investigation in the way that would give me the best results. In my pre test I decided to see:

  • Which voltage is the best to use 1v, 3v or 5v.
  • Which length of wire to use.
  • Which lengths of the wire to measure.
  • Which apparatus to use.
...read more.


– A micrometer is a measuring device, which cans hkjgkhjlkhjkhjkhjkhienable the user to measure to 100th of an iiiiiiiiiiiiiiiiiiiiiiiiiimpmillimetre.


Step-by-Step Method

  1. Set up the apparatus as shown on the previous page.
  2. Measure the widths of the five wires using a micrometer at 250mm, 500mm and 750mm and then take the average width.
  3. Turn on the power pack.
  4. Ensure that the voltage is 3v.
  5. Record the current from the ammeter.
  6. Repeat steps 3 to 5.

Fair Test

To help me make my test fair I had already made the circuit up to check that the circuit works and that the resistance changes when different wires with different widths were used. I will take more than one set of values making sure that the set-up is the same each time. I need to make sure that I only change the wires and that the other variables

...read more.



In the experiment I received some anomalous results, however in most cases the results were not far out since the points are either on the line of best fit or are close to it. The only obvious anomaly was in the graph “The average diameter of a wire against its resistance” but this could be an error either in the obtaining of the data or the recording of the data and therefore I will not account it.

To reduce anomalous results, I would try to keep the temperature of the wires equal, since as the temperature increases the resistance of the wire increases. I could do this by recording the results 1 minute after the wire has been connected to the circuit.  Also measuring the length of the wire more accurately perhaps with the use of callipers would improve the accuracy of my readings.

Another limitation was that we could not measure the wire accurately, as it was not straight though we tried to make it as straight as possible and our rulers, were not accurate enough.

I feel that the use of a micrometer greatly aided the investigation it helped us to obtain extremely accurate results.

To further this investigation I would change the type of metal used and see if I could draw the same pattern of the resistance being proportional to the potential difference with a variety of metal wires.

Given the research, and the limited results of my experiment, it appears that a firm conclusion can be draw, that resistance is proportional to the size of the diameter of a wire.

...read more.

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