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Resistance of a wire

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During my investigation there will be several factors that I will need to control or keep constant, to ensure that my results are as reliable as possible. Two of these factors are the current and voltage output. These two factors contribute to the amount of resistance in the circuit, meaning that I will have to keep both at a constant value, to be able to observe and record the effect of the length of wire on the resistance in the circuit. By using a resistor and an ammeter in my circuit, I will be able to dictate the rate of the current flowing through it. By using the same voltage batteries every time in my investigation, I will also be able to ensure that the voltage in the circuit is the same each time.

I will also ensure that the external temperature throughout my investigation remains at an approximate constant. This is because increased temperature affects the vibration of the atoms within the wire, and therefore affects the resistance.

Preliminary Investigation

I decided to carry out a preliminary investigation, so that I understood exactly what I would need to do during the real investigation. Primarily, I have chosen to

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To measure the length of wire accurately.

Scissors - To cut the wire to the required length, with precision.


  1. Firstly, I shall assemble the circuit, following my illustration checking that every piece of equipment is working properly and in the correct position. I will use two batteries at a voltage of 7 volts each.
  2. Then I shall measure and cut a 100cm length of Nickel wire using the metre ruler and scissors.
  3. I shall attach this to the circuit, using the crocodile clips, and then adjust the variable resistor, so that the reading on the digital ammeter is 0.35. I have decided on this value for the current, as it is the highest achievable value that will pass through every length of wire that I am testing.
  4. Once I have adjusted the variable resistor, I will record the reading on the voltmeter, and then calculate the resistance in the circuit from this, using the equation I noted in my strategy.
  5. I will then repeat the process for lengths of wire 80cm, 60cm. 40cm, and 20cm. I have decided to do it in decreasing order, because it will save wire and time.
  6.  After doing this, I will repeat the whole process twice more, as this will ensure that my results are as accurate and reliable as possible.
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The results I collected complied with my hypothesis for a good reason:

The electrical resistance of a wire would be expected to be greater for a longer wire and less for a wire of larger cross sectional area because of the laws of resistivity and resistance. The resistance of a wire can be expressed as:

        R = pL


Where p = resistivity

        L = length

        A = Cross sectional area

(Note: Resistivity is the natural resistance of a material, disregarding its length or cross sectional area.)

This equation shows that increasing the length of a material will increase its resistance. This happens because metals consist of atoms in a lattice formation, each with a shell of electrons. The outer electrons are free to move away from their original atoms and travel through the lattice, creating a flow of electrons. When a voltage is applied across the metal, the electrons drift from one end of the conductor to the other under the influence of the electric field.

At room temperature, the vibration of ions in the structure of the conductor is the primary source of collisions with electrons and therefore the main cause of metal resistance.

The larger the cross-sectional area of the metal, the more electrons are available to carry the current, so the lower the resistance. The longer the conductor, the more collisions occur in each electron's path through the material, so the higher the resistance.

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This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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