To investigate the effect of changing physical properties has on the resistance of a piece of wire.

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Kieran Wood        Resistance of a wire Experiment        2001-09-04

Mr Hodgson        

Aim:  To investigate the effect of changing physical properties has on the resistance of a piece of wire.

Variables:  The variables are:

      Temperature

                      Length of wire

                      Diameter of wire (cross sectional area)

                      Material of wire

These will all affect the resistance of the wire.

The temperature will affect the resistance of the wire because as the temperature of the wire increases the metal will expand. This will affect the diameter and length of the wire. Also as the wire gets hotter the static particles get more energy and so vibrate more. This causes the average space they take up to increase and so there is a greater chance of a collision between them and an electron.

The length of the wire will affect the result because if the wire is longer there are more particles for the flowing electrons to collide with, which in turn slows down the electrons and so the resistance is greater. They slow down because at each collision some kinetic energy is transferred into heat energy.

The diameter of the wire will affect the result in the opposite way as the length. The thicker the wire the more open spaces in the wire for the electrons to flow through and so decreases the resistance of the wire.

Different materials have different densities. With a higher density there are more static particles in the way and so the chance of a collision is increased. A collision affects the resistance as explained before.

The variable I intend to investigate is the length of the wire. Therefore I will keep the other variables the same to make my results accurate.

 

To make my experiment a fair test, I will:

                

  • Use the same equipment for each test,
  • Use the same wire for each test,
  • Keep the voltage the same for each test,
  • Make sure I press down on the wire with the same amount of force each time,
  • Only change the length of the wire,
  • Let the wire cool down between tests so the temperature does not become a variable,
  • Keep the circuit set up the same for each test

        To get accurate readings I will first do a preliminary test to decide on a set of parameters to follow eg, the length wire, voltage setting or the amount of time I should leave the volt and amp meters to settle. If these parameters do not produce accurate results (eg, wire gets too hot or results not varied enough to support a conclusion) I will change one of the parameters until the results can be recorded accurately.

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The range of lengths I will use for the experiment are 100-600mm of wire. The lengths I will use are 100, 200, 300, 400, 500, 600mm. I will use a 2-volt setting.

For reliability I will repeat each test, at each length, three times making at least 18 tests. If I find, as I am plotting my results, there it a reading that does not fit the expected pattern I will repeat that test for a fourth time and discount the wrong result in my conclusion.

Prediction:  I predict that the longer the wire the higher the potential across ...

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