Resistance of a Wire Investigation

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Michael Laws                01/05/07

INTRODUCTION

I have been given the task to investigate how the resistance of a wire is affected by the length.  I will investigate, predict possible results, do the experiment and analyse assess my results to my degree of judgement and knowledge.  Any analogous result I will record and investigate why they are abnormal.  I will also try to find any correlation between my results.

SCIENTIFIC BACKGROUND

         I had very little knowledge about this subject before this coursework came along.  I did a small amount of work in Design and Technology last year.  

The resistance of a conductor depends on two things:

  1. Its dimensions
  2. The material it is made of

  1. A thin wire has a high resistance than a thick wire. A long wire has a greater resistance than a short one

  1. The material the conductor is made of affects its resistance.  A good conducting material has more ‘free electrons’ in the outer shell of their structure.  If the electrons can flow easily through this material, it is resistance is lower.

For example, gold has more free electrons than iron, because of this   it is a better conductor.

This Information is from the book ‘Physics Know How’.  Written by John Harrison

The resistance is measured in ohms.  Ohms (R) is equal to the electromotive force or potential difference, in volts (V) divided by the current in amperes (I).

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.  These bonds are called covalent bonds.  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.

When a metal wire is placed in an electric circuit, the voltage from the battery makes the electrons flow through the wire.  The free electrons are given energy; as a result, they move and collide with neighbouring free electrons.  This slows down the flow of electricity.  This happens across the length of the wire and thus electricity is conducted through it.  Resistance is a measure of how easily the electrons can move through the metal.  A low resistance means that the electrons can move easily.

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Electric current is a measure of the charge that flows per second.  As the charge on each electron is the same, the current is the number of electrons flowing per second.  If the resistance is high, the flow of electrons is slowed down, thus the number of electrons per second is reduced. i.e. the current is reduced.

If the metal is heated, the metal ions will vibrate more.  This means that there is a higher chance of the electrons bumping into a metal ion so the flow of electrons is reduced. i.e. the resistance is increased.  

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