Physics Coursework Investigating Resistance of wires and its relationship to length.

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Physics Coursework

Investigating Resistance of wires.

For my physics coursework I am investigating the resistance of wires.  When a metal wire is placed on an electric circuit the voltage from the battery makes the electrons flow through the wire. As they do so, they collide with the metal ions and this process slows down the flow. Resistance is a measure of how easily the electrons can move through the metal, a low resistance means that the electrons can move easily so a high resistance means that the electrons can’t move very easily.  

        

Atoms are made up of a positively charged nucleus surrounded by negatively charged electrons. In solids one or two of the outer electrons in each atom are used to form the bonds between atoms that hold the solid together. In a metal these bonding electrons are free to move through the entire solid. These are often referred to as free electrons. An electric current is a flow of charged particles and when a voltage is applied to a metal, the free electrons can flow through the metal. This is shown in the diagram above. This is the basis of my investigation.

The factors that alter resistance are:

  • The diameter of the wire - the bigger the wire the lower the resistance because there is a larger amount of space for the electrons to move which means there are less collisions with the ions.
  • The length of the wire - the longer the wire the higher the resistance because there is a smaller amount of space for the electrons to move which means there are more collisions with the ions.
  • The temperature - the higher the temperature of the wire the higher the resistance because the high temperature causes more electron and ion collisions.
  • The material - the better the conductor the lower the resistance, because some materials are just better than others.

I used Ohms law (V=IR, voltage = current ×resistance) to work out the resistance. However V=IR does not tell me the resistance so I had to change the equation to R=V/I (resistance = voltage ÷ current) in order to get the resistance.

I considered all my factors and I decide I was not going to do:

  • Temperature because it is unreliable. Temperature will either be the controlled variable or fixed to make it a fair test.
  • Diameter because my school is unable to source 8 or 9 different thicknesses
  • Material because it will be unreliable because the material results would be too spread out as all the materials, Nichrome, Constantin, Copper and Tin, are very different.
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I decided I would have the length as my independent variable and the length would vary from 200mm to 1000mm. I had the resistance as my dependant variable.

The experiment circuit:

        

Preparing for Practical

Before I started the actual test, I needed to decide what material to use and what voltage to have on the power pack. The voltage on the power pack goes from 2-12 but I decided to set the power pack voltage to 2, because any higher and the wire would have gotten hot therefore making ...

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