davisnotes/elec_condins.html

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<title>Electricity - Conductors and Insulators - Physics 299</title>
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<h1> <img src="ULPhys1.gif" align="texttop" height="50" width="189"></h1>
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<h1>Conductors and Insulators</h1>
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<center><img src="celticbar.gif" height="22" width="576"><br>
<br>
<font color="#ff0000"><i>"What is the use of a new-born child ?"</i></font><br>
Benjamin Franklin<br>
<small><small>(when asked what was the use of &nbsp;a new invention)</small></small><br>
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<ul>
<li> Moving electric charges constitute what is know as an electric
current.&nbsp; It is the electric currents in semi-conductor devices
which are responsible for the electronic technology in today's society.<br>
<br>
</li>
<ul>
<li> <b>Conductors</b> are materials which allow the free movement
of electric charge.&nbsp; Examples include,</li>
<ul>
<li> Metals</li>
<li> Some liquids</li>
<li> Gas plasmas<br>
<br>
</li>
</ul>
<li> <b>Insulators</b> (or non conductors) are materials which
provide
significant resistance to the flow of electric charge.&nbsp; Examples
include,</li>
<ul>
<li> Non metals - plastic, wood, glass, rubber etc.</li>
<li> Gases<br>
<br>
</li>
</ul>
<li> <b>Semi-conductors</b> are materials whose resistance to
current flow
falls between conductors and insulators.&nbsp; There are very few such
materials, but their importance in electronic technology cannot be
emphasized enough.&nbsp; Examples,</li>
<ul>
<li> Silicon</li>
<li> Germanium<br>
<br>
</li>
</ul>
</ul>
<li> <b>Mechanisms of conduction:</b><img src="science.gif"
align="middle" height="32" width="288"> </li>
<ul>
<li> Metals (solid)</li>
<ul>
<li> Each atom in the solid is "fixed", forming a lattice.</li>
<li> Outer electrons in a metal are weakly bound to the atomic
nucleus.</li>
<li> When an external electric field is applied these outer
electrons move
through the material creating an electric current.</li>
</ul>
<li> Liquid conductors and gas plasmas</li>
<ul>
<li> Conducting liquids and gases are comprised of positive and
negative
ions (charged particles).</li>
<li> Both positive and negative ions move when an external
electric field
is applied, thus creating the current.</li>
<li> A positive charge moving to the right creates the same
current as
an equal negative charge moving to the left.</li>
</ul>
<li> Insulators</li>
<ul>
<li> All electrons in these materials are tightly bound to the
atomic nuclei.&nbsp; External electric fields are typically not large
enough to cause any flow of charge.</li>
</ul>
<li> Semi-conductors</li>
<ul>
<li> These materials have a small number of weakly bound
electrons, the
number of which is very&nbsp; dependent on the temperature and
potential
difference applied across the material.</li>
<br>
&nbsp;
</ul>
<li> It is important to realise that because sustained electric
currents
only occur when a potential difference is maintained in a closed
circuit,
as many charge carriers enter as leave any part of the circuit.&nbsp;
In
other words electric current is not "used up"; it has the same value
everywhere in the circuit.<br>
<br>
</li>
</ul>
</ul>
<p><br>
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<p class="MsoNormal"><span
style="color: rgb(255, 0, 0); font-style: italic;">Marilyn Monroe
suggests to Einstein: What do you say,
professor, shouldn't we marry and have a little baby together: what a
baby it
would be - my looks and your intelligence!</span><br
style="color: rgb(255, 0, 0); font-style: italic;">
<span style="color: rgb(255, 0, 0); font-style: italic;">Einstein: I'm
afraid, dear lady, it might be the other way around...</span><br>
Albert Einstein<br>
</p>
<img src="celticbar.gif" height="22" width="576"> <br>
&nbsp;
<p><i>Dr. C. L. Davis</i> <br>
<i>Physics Department</i> <br>
<i>University of Louisville</i> <br>
<i>email</i>: <a href="mailto:c.l.davis@louisville.edu">c.l.davis@louisville.edu</a>
<br>
&nbsp; </p>
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