148 lines
4.8 KiB
HTML
148 lines
4.8 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//w3c//dtd html 4.0 transitional//en">
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<html>
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<head>
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<meta http-equiv="Content-Type"
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content="text/html; charset=ISO-8859-1">
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<meta name="GENERATOR"
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content="Mozilla/4.7 [en] (X11; U; OSF1 V4.0 alpha) [Netscape]">
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<meta name="Author" content="C. L. Davis">
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<title>Electricity - Conductors and Insulators - Physics 299</title>
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<meta content="C. L. Davis" name="author">
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</head>
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<body style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);"
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alink="#ff0000" link="#0000ee" vlink="#551a8b">
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<center>
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<h1> <img src="ULPhys1.gif" align="texttop" height="50" width="189"></h1>
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</center>
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<center>
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<h1>Conductors and Insulators</h1>
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</center>
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<center><img src="celticbar.gif" height="22" width="576"><br>
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<br>
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<font color="#ff0000"><i>"What is the use of a new-born child ?"</i></font><br>
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Benjamin Franklin<br>
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<small><small>(when asked what was the use of a new invention)</small></small><br>
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</center>
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<img src="netbar.gif" align="middle" height="40" width="100%"> <br>
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<center><img src="misc1.gif" align="middle" height="32" width="288">
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</center>
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<ul>
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<li> Moving electric charges constitute what is know as an electric
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current. It is the electric currents in semi-conductor devices
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which are responsible for the electronic technology in today's society.<br>
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<br>
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</li>
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<ul>
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<li> <b>Conductors</b> are materials which allow the free movement
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of electric charge. Examples include,</li>
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<ul>
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<li> Metals</li>
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<li> Some liquids</li>
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<li> Gas plasmas<br>
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<br>
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</li>
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</ul>
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<li> <b>Insulators</b> (or non conductors) are materials which
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provide
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significant resistance to the flow of electric charge. Examples
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include,</li>
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<ul>
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<li> Non metals - plastic, wood, glass, rubber etc.</li>
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<li> Gases<br>
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<br>
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</li>
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</ul>
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<li> <b>Semi-conductors</b> are materials whose resistance to
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current flow
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falls between conductors and insulators. There are very few such
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materials, but their importance in electronic technology cannot be
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emphasized enough. Examples,</li>
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<ul>
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<li> Silicon</li>
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<li> Germanium<br>
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<br>
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</li>
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</ul>
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</ul>
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<li> <b>Mechanisms of conduction:</b><img src="science.gif"
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align="middle" height="32" width="288"> </li>
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<ul>
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<li> Metals (solid)</li>
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<ul>
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<li> Each atom in the solid is "fixed", forming a lattice.</li>
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<li> Outer electrons in a metal are weakly bound to the atomic
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nucleus.</li>
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<li> When an external electric field is applied these outer
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electrons move
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through the material creating an electric current.</li>
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</ul>
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<li> Liquid conductors and gas plasmas</li>
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<ul>
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<li> Conducting liquids and gases are comprised of positive and
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negative
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ions (charged particles).</li>
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<li> Both positive and negative ions move when an external
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electric field
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is applied, thus creating the current.</li>
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<li> A positive charge moving to the right creates the same
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current as
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an equal negative charge moving to the left.</li>
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</ul>
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<li> Insulators</li>
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<ul>
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<li> All electrons in these materials are tightly bound to the
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atomic nuclei. External electric fields are typically not large
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enough to cause any flow of charge.</li>
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</ul>
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<li> Semi-conductors</li>
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<ul>
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<li> These materials have a small number of weakly bound
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electrons, the
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number of which is very dependent on the temperature and
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potential
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difference applied across the material.</li>
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<br>
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</ul>
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<li> It is important to realise that because sustained electric
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currents
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only occur when a potential difference is maintained in a closed
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circuit,
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as many charge carriers enter as leave any part of the circuit.
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In
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other words electric current is not "used up"; it has the same value
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everywhere in the circuit.<br>
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<br>
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</li>
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</ul>
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</ul>
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<p><br>
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<img src="netbar.gif" height="40" width="100%"> </p>
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<center>
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<p class="MsoNormal"><span
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style="color: rgb(255, 0, 0); font-style: italic;">Marilyn Monroe
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suggests to Einstein: What do you say,
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professor, shouldn't we marry and have a little baby together: what a
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baby it
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would be - my looks and your intelligence!</span><br
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style="color: rgb(255, 0, 0); font-style: italic;">
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<span style="color: rgb(255, 0, 0); font-style: italic;">Einstein: I'm
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afraid, dear lady, it might be the other way around...</span><br>
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Albert Einstein<br>
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</p>
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<img src="celticbar.gif" height="22" width="576"> <br>
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<p><i>Dr. C. L. Davis</i> <br>
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<i>Physics Department</i> <br>
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<i>University of Louisville</i> <br>
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<i>email</i>: <a href="mailto:c.l.davis@louisville.edu">c.l.davis@louisville.edu</a>
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<br>
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</p>
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<p><img src="header-index.gif" height="51" width="92">
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</p>
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</center>
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<p><br>
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</p>
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</body>
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</html>
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