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Investigating the factors effecting resistance of a wire.

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Investigating the factors effecting resistance of a wire


Resistance is how easily electron flow through a component. Electric current is the movement of electrons through a conductor. So the action of particles slowing down the flow of electrons is resistance.

This happens because of the electrons that flow through the wire. These electrons travel at a steady pace in one type of wire, but when they come to a different piece of wire, they have to slow down or speed up in order to be able to pass. (This is why the current differs). Ohm's law states that the current flowing through the circuit is directly proportional to the voltage applied. (If you double one, you double the other.) Resistance is encountered when the charged particles that make up the current collide with other fixed particles in the material. As the resistance of a material increases so must the force required to drive the same amount of current. In fact resistance, in ohms is equal to the electromotive force or potential difference, in volts (V) divided by the current, in amperes (I) - Ohm's law.

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 more free electrons means a better 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 and as a result move and collide with neighbouring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss as heat. It involves collisions between the free electrons and the fixed particles of the metal, other free electrons and impurities.

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  1. 80cm length of 36 SWG diameter “nichrome” (a metal alloy) wire- to measure the resistance across the wire you need wire. There needs to be 80cm even though we will only be using 50cm because then you have some room to put the wire into the crocodile clip.
  2. Power pack- to supply the power and electrons through the nichrome wire to make a reading from the ammeter and voltmeter.
  3. Five connecting wires- to connect the nichrome wire to the ammeter and voltmeter and to connect the ammeter and voltmeter to the power pack.
  4. Two crocodile clips- to attach the connecting wires to the constantan wire.
  5. Voltmeter meter- measures the voltage (measured in colts) across the nichrome wire.
  6. Ammeter meter- measures the current (measured in amps) across the nichrome wire.


Fair Test

Use the same wire throughout the experiment, to keep diameter exactly the same. Use an ammeter and a voltmeter to measure the figures accurately and to 2 decimal places. I would do the experiment in the same environment every time, so the temperature would be the same, so the resistance of the wire is not changed.

To keep this experiment as accurate as possible we need to make sure, firstly, that the length of the wire is measured precisely from the inside edge of the crocodile clips, making sure that the wire is straight when we do this. We must also make sure that the wire is straight when we conduct the experiment. If it is not, short circuits may occur and bends and kinks in the wire may affect the resistance. The reading that we take of the voltage should be done fairly promptly after the circuit is connected.

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So the length of the wire does affect the resistance of the wire because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion.

In any given metal wire, there are a number of atoms and free moving electrons. Electricity is the movement of these electrons through the wire. Resistance is caused when the free electrons moving through the wire collide with the atoms making their path through the wire more difficult. This means that if there are more atoms in the way to collide with the free electrons the resistance is increased. In a length of wire there will be a number of atoms, and in a wire twice the length, there will be twice the number of atoms. In turn this will lead to there being double the number of collisions between the electrons and the atoms increasing the resistance by 2. This explains why the results were directly proportional. If a length of a wire contains a certain number of atoms when that length is increased the number of atoms will also increase. This is shown in my diagrams below:

In this diagram the left wire is half the length of the wire on the right and so has half the number of atoms, this means that the electrons will collide with the atoms half the amount of times.
Also if the length of the wire was trebled or quadrupled then the resistance would also treble or quadruple.

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