What affects the current running through a length of wire?

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Physics Investigation - What affectsthe current running through a length of wire?

This coursework will investigate the answer to the above question. There are five variables, which will affect the outcome:

  • Diameter of the wire;
  • Length of the wire;
  • Which metal is the wire made of;
  • Temperature of the wire;
  • Potential difference passed through the wire.

Hypothesis.

I predict that as the length of the wire increases, the resistance will also increase. Hence, the current will decrease as the wire gets longer. Therefore I can also predict that, as the length doubles, the resistance will also double, and therefore the current will half.

I think this is because of the theory of resistance.

As the atoms in a metal join together, they share electrons, similar to covalent bonding. This creates a 'sea' of delocalised electrons; it is these free electrons, which carry the electric charge when a metal is conducting. The atoms create a sturdy structure in the form of a lattice, which enables the metal to withstand high temperatures. Hence metal wires do not melt when electric current is passed through them.

The theory of resistance states that, as the charged, delocalised electrons move through the lattice, they collide with atoms in the structure. The electrons transfer some of their energy to the atoms; this slows the atoms down. In any given 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 of the wire collide with the atoms in their path, making their path more difficult. This means that if there are any 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 twice the wire 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 atoms, increasing the resistance by 2. This explains why the results were directly proportional. For example, a wire 10cm long may have 500 atoms blocking the electrons. Therefore in a wire 20cm long, there would be a thousand atoms, meaning that the resistance has doubled.

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This supports my hypothesis because, as the wire gets longer, there will be more atoms for the electrons to collide with. Therefore the electrons will get slower as the resistance increases, so the current decreases.

The resistance of a wire is calculated by using both the current, and the potential difference from within the circuit. The measurements are fed into this equation:

V = I R                        V = Voltage, I = Current, R = Resistance.

The equation can be arranged to:

                R = V        

                        I

Ohm's Law.

Ohm's Law, is also relevant to know. This states ...

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