To see how the length of a wire affects its resistance. To find the wire to test, I'm going to test 4 different types of wire in another experiment

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`Resistance of a wire –Electricity Coursework

Aim:

 To see how the length of a wire affects its resistance.

To find the wire to test, I’m going to test 4 different types of wire in another experiment and use the one with the highest resistance.

The Theory behind the Experiment

Theoretically the length of a wire should affect its resistance.

        Electricity encounters a certain amount of obstruction when passing through a wire depending on its length, width, temperature and type of metal, this obstruction is called the resistance and is measured in ohms.

        The longer and thinner the wire the harder it is for the electrons to flow through, because there are less spaces for it to flow through and more obstructions along the length. It has a similar principal to the flow of water and how it is impeded when passing through a long and narrow pipe. Therefore the longer the wire is the more resistance there should be.

        The other factor that can affect the resistance is the metal type, for example the resistance of an Iron wire is about seven times greater than that of a copper wire with the same dimensions, and this is because of the varied amount of ions in the different metal, more ions in Iron mean that electrons find it harder to pass through. This is the reason why copper is used in electrical wire; because it gives little resistance less energy is used to make it flow. I need to test 4 different wires in the first experiment; to find the type of wire with most resistance. It is important that for both experiments I let the wire cool down for a few seconds after taking the reading, as temperature can affect the resistance. This is because the molecules in the wire when heated vibrate more and the electrons find it harder to pass through, thus the resistance will increase.

        When connecting the circuits for both experiments I need to make sure the voltmeter is in parallel with the wire and the ammeter is in series. This is shown in a diagram of apparatus later on.

        George Simon Ohm (1789-1854) was one of the first people to investigate current and voltage and came up with the following law for metallic conductors.

        The current through a conductor is proportional to the potential difference between its ends, provided that physical conditions, such as temperature, remain constant: i.e.

                V/I = constant (resistance).

Where v = voltage and I = current.

        This means regardless of the size of the current, as long as there is no temperature change the resistance of a wire remains constant. The law is based on experiment (empirical) and holds remarkable accuracy for metallic conductors which are what I’m going to use in my experiment.

        It is important to note that the circuits I will be using for my experiments are in series because in parallel and series circuits the methods for calculating the total resistance for more than one component are different. In series the resistance across the components are added together: R = R1+R2. Whereas in Parallel the current divides, the larger part going through the smaller resistance and the smaller part through the larger resistance: 1/R=1/R1 + 1/R2. So the resistance is smaller because it is like a single wire with a large cross section and therefore more spaces in the atoms for the electrons to pass through.

        I’m going to prove that resistance is proportional to length. The greater the cross sectional area of the conductor the more electrons available to carry the charge along the conductor’s length and so the lower the resistance is. Resistance is inversely proportional to cross sectional area.

Key Variables:

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Outline Plan

1st experiment

  • We have four different types of wire attached to two metre rules they are: Manganin, Nichrome, Copper and Constantan.
  • We will measure the current and voltage for each wire separately, one after the other.
  • To make it a fair test we will make sure there are no changes in the temperature, thickness, or length that would affect our experiment for reasons explained earlier in “The theory behind the experiment”. The voltage will also be kept at 2v for each test to prevent over heating of the wires ...

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