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In this investigation, I will study the link between the diameter of a wire and its resistance. I believe that as the diameter of the wire increases, the resistance of the wire will decrease.

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Physics Coursework

Investigation into Resistance


In this investigation, I will study the link between the diameter of a wire and its resistance. I believe that as the diameter of the wire increases, the resistance of the wire will decrease.

Electricity is conducted through a conductor, in this case wire, by means of free electrons. The number of free electrons depends on the material and the more free electrons the better the conductor, i.e. it has less resistance. For example, gold has more free electrons than iron and, as a result, it is a better conductor. The free electrons are given energy by the cell/battery and as a result move and collide with neighboring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss. It involves collisions between the free electrons and the fixed particles of the metal, other free electrons and impurities. These collisions convert some of the energy that the free electrons are carrying into heat. If the cross-sectional area of the wire doubles, there will be twice as many atoms and twice as many electrons bumping into them, but also twice as many electrons getting through, twice as many gaps. If there are twice

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5 x Wires  

To connect the circuit together.

Wires of varied thickness (22, 24, 26, 28, 30 SWG)

To test my hypothesis

2 x Crocodile Clips

To connect the various thicknesses of wire to the circuit

1 x Ruler

To connect the various widths of wire to, to make sure that the length doesn’t vary which could affect the resistance.

Through using the same circuit I could have tested a number of different things that affect resistance to find the relationship between resistance and the following:

  1. Temperature - When the temperature of a metal increases the resistance of that metal increases. This is because when the temperature increases the atoms of the metal vibrate more vigorously, due to the increase in energy. This means that the electrons have more difficulty getting through the wire as they collide with the atoms which are in their pathway.  This increases the amount of collisions, therefore there is more resistance. However it is hard to keep the temperature exactly the same as the room temperature might change from day to day. I did not investigate temperature because it is hard to control the range of temperature needed without the correct apparatus, which I don’t have. 
  2. Length of wire - The longer the length of the wire, the greater the resistance.
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  • For any 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.
  • It is possible that the batteries were providing a different voltage for some of the results. This is unlikely to be a problem as whatever the voltage is the resistance should stay the same.
  • If you take into account one of the factors that Ohm’s Law applies, then another possible explanation could be that at some point the wire was not allowed to cool completely, so that the temperature was higher for that measurement. Whilst unlikely (due to the two repeats of results), this would cause a higher resistance as explained previously.

To improve my results I could have also used pointers instead of the crocodile clips which I used for connecting the wire. I would do this because pointers are a lot more accurate, they have a smaller surface area on their tips than crocodile clips. This in effect would give much more accurate measurements.

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