Resistance of Wire

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Physics coursework

Resistance of Wire

Aim

The aim of this investigation is to investigate the resistance of a wire by using one of the factors, which will have an affect on the resistance.

Variables

Resistance of wire can be affected by the following factors:

  • Length of wire
  • Make of wire
  • Diameter of wire
  • Temperature of wire

The variable in which I will change for my investigation will be the LENGTH of the wire.  I have chosen this variable to change, as it will be easy to measure and to do.

Background

Resistance is calculated with the following equation:

Resistance (in ohms) = Voltage (in volts) / Current (in amps)

As the electrons in an electric current move around a circuit, they bump into atoms in the wires.  Atoms of different elements hold up the electrons to different extents.  For example, electrons pass easily through copper wire, but much less easily through tungsten or nichrome wires.  We say that copper has a lower resistance than tungsten or nichrome.

Resistance is anything in the circuit which slows down the flow of electrons / currents.  It is a sort of constriction in the flow.  

The unit of resistance is the ohm (Ω) and the standard abbreviation for resistance is R.

The factors which affect the resistance of a wire are:

The lengths of the wire

The cross sectional area of the wire

The type of material

The temperature

If there was a long thin piece of wire and a short thick piece of wire, the long thin one will have a higher resistance compared to the short thick wire.  The reason for this is because the longer and thinner the wire, the more atoms of the material the current will have to travel pass, therefore the harder to get through the wire.  If the wire was short and thick, then the current would flow through the wire easily having a lower resistance (as less atoms to pass through).

Different materials also have an affect on the resistance.  Metals contain free electrons which move around freely in-between atoms.  These make the metals become good conductors whereas non-metals are poor conductors, as they contain no free electrons (their electrons are attached firmly with their atoms).  Good conductors have a lower resistance compared to poor conductors, which have a higher resistance.  Also, less reactive the metal is, the better it is at conducting (lower resistance).  Silver is the best conductor but as it is expensive to purchase, cheap copper (the second best) is used instead.  

The temperature also affects the resistance of a wire.  In hot conditions, the resistance is lower and in cold conditions, the resistance is higher.   When hot, the electrons react faster causing it to vibrate faster passing on the energy / electricity along quicker across the wire and vice versa.

Note:  I have found all the resistance information from the books: GCSE Physics by Tom Duncan, and Letts Science GCSE by Graham Hill.  

Fair test

I will do many things to make my investigation fair.  For each experiment, I will use the same thermometer, power pack, voltmeter, ammeter, cables / wires and the same beaker for the water.  The type of wire I will use will also be the same and I will carry out the same experiment three times for each length of wire, making the results more accurate and reliable.  Also, I will need to make the other variables, which will affect the resistance of a wire, the same all the time, making the experiment fair.  To do this, I will obviously use the same type of wire and therefore the same thickness.  To keep the temperature the same, I will have a beaker full of water, and carry out the experiment with the wire inside the water, meaning the temperature of the wire will always be kept constant.  

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When doing the actual experiment, I must also make sure that the wire inside the water does not touch itself otherwise it will short circuit, meaning the experiment will be unfair.

Apparatus

For this investigation, I will use the following:

  • A power pack

  • An Ammeter to measure the current

  • A Voltmeter to measure the voltage

  • A beaker full of water

  • A thermometer

  • Some wire – 22swg. Const 125g

  • Crocodile clips

  • Wires/ cables

  • Pen and paper

Prediction

For my investigation, I predict that the longer the wire, the higher the resistance will be. ...

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