Resistivity in a wire coursework

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Tony Tien 11s

Planning:

I am going to investigate how the thickness of copper wire affects the resistance through it. For this investigation, I am going to use copper wire and electricity to test the resistance. When I pass electricity through a copper wire, resistance is created which slows down the flow of electrons.

If a component has a high resistance, it is more difficult for a charge to flow through it. The electrons will end up making many collisions with ions.

If there is a potential difference across a conductor, a current goes through it. However, when you apply the same p.d. across different conductors, the currents are different.

Resistance is measured in ohms (Ω) and is defined as:

‘The resistance of a conductor is the ratio of the p.d. applied across it, to the current passing through it.’

Resistance, R =     p.d. across the conductor, V (volts)  

                          Current through the conductor, I (amps)

R = V               V = I R

        I

To find the resistance of a wire, it must be placed in a circuit with a voltmeter parallel to the wire. The circuit must also contain an ammeter and a variable d.c. supply. The voltmeter is used to find the p.d. across the wire and the ammeter is used to find out the current through the wire. Then the resistance can be calculated using the formula with the two meter readings.

Georg Ohm discovered that: ‘The current through a metal wire is directly proportional to the p.d. across it (providing the temperature remains constant).’ This is called Ohm’s law. Materials that obey this law are called ohmic conductors.

Factors:

There are four factors that affect the resistance a wire has. These are:

  • Type of wire
  • Length of wire
  • Cross sectional area
  • Temperature

All metals are good at conducting electricity but some are better than others. Also, a longer wire has more resistance than a short wire. Furthermore, a thick wire has less resistance than a thin wire. Additionally, a hot wire has more resistance than a cold wire.

If resistance occurs as the result of collisions between free electrons and ions in the wire, then there is likely to be more collisions in a longer wire because there will be more ions.

Metals contain a large number of free electrons. As these free electrons move through the wire, they collide with metal ions that are vibrating. These collisions oppose the flow of electrons and therefore, the wire has resistance. As the wire becomes hotter, the ions vibrate more which makes it more difficult for electrons to pass so the resistance has increased.

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Furthermore, the cross-sectional area affects the resistance because if the wire is thick, more free electrons will be able to flow. This is the same with water flowing through a big pipe.

The other factor that is known to affect the resistance is the material that a wire is made of. Not all materials are created equal in terms of their conductive ability. Some materials are better conductors than others and offer less resistance to the flow of electrons.

If a wire is at a constant temperature, its resistance depends on its dimensions and the material from ...

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