118 lines
4.6 KiB
HTML
118 lines
4.6 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" content="text/html;
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charset=windows-1252">
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<meta name="GENERATOR" content="Mozilla/4.7 [en] (X11; U; OSF1 V4.0
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alpha) [Netscape]">
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<meta name="Author" content="C. L. Davis">
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<title>Electricity - Electric Dipole in an External Field - Physics
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299</title>
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</head>
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<body style="color: rgb(0, 0, 0); background-color: rgb(255, 255,
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255);" link="#0000ee" alink="#ff0000" vlink="#551a8b">
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<center>
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<h1> <img src="ULPhys1.gif" height="50" align="texttop"
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width="189"></h1>
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</center>
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<center>
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<h1>Electric Dipole in an External Electric Field <br>
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</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>"</i></font><font color="#ff0000"><i>
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<meta http-equiv="content-type" content="text/html;
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charset=windows-1252">
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When you look at yourself from a universal standpoint,
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something inside always reminds or informs you that there are
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bigger and better things to worry about."</i></font><br>
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Albert Einstein<br>
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</center>
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<img src="netbar.gif" height="40" align="middle" width="100%"> <br>
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<ul>
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</ul>
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<ul>
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<li>We have already considered the electric field <i><b>created</b></i>
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by an electric dipole. Now we consider the behavior of an
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electric dipole placed in a uniform (constant) electric field.</li>
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</ul>
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<div align="center"><img alt="elec dip in external field"
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src="elec_dip_exte.gif" height="157" width="323"><br>
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<br>
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<div align="left">
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<ul>
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<li>Note that since the force on each of the charges are equal
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in magnitude but opposite in direction there is <b>no net
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force on the dipole</b>.</li>
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</ul>
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<ul>
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<li>However, since the two forces are not concurrent, there is
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a non-zero torque about the center of the dipole given by,</li>
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</ul>
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<div align="center"><img alt="elec dip ext e eqn1"
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src="elec_dipexte_eqn1.jpg" height="45" width="117"><br>
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<br>
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<div align="left">
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<ul>
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<li>Using the definition of the work done by a torque
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(rotational force), it can be shown that the
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electrical potential energy stored by a dipole in an
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external field is given by,</li>
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</ul>
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<div align="center"><img alt="elec dip in ext e eqn2"
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src="elec_dipexte_eqn2.jpg" height="41" width="117"><br>
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<div align="left">
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<ul>
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<li><img alt="hot" src="hot.gif" height="43"
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align="middle" width="79">A dipole placed in a
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uniform electric field will rotate until it is
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aligned "-" to "+" along the field - this is the
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lowest energy configuration.</li>
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</ul>
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<ul>
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<li><img alt="exclamation" src="exclamation-icon.gif"
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height="30" width="31"> If the external
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field is not uniform, the net force will not be
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zero.<br>
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</li>
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</ul>
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</div>
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</div>
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</div>
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</div>
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</div>
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</div>
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<ul>
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</ul>
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<ul>
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</ul>
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<div align="center"> </div>
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<div style="text-align: left;"><img src="netbar.gif" height="40"
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width="100%"> </div>
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<center><span style="font-size: 12pt; font-family: "Times New
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Roman";"><span style="color: rgb(255, 0, 0); font-style:
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italic;"></span></span><span style="font-size: 12pt;
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font-family: "Times New Roman";"><span style="color:
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rgb(255, 0, 0); font-style: italic;">
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<meta http-equiv="content-type" content="text/html;
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charset=windows-1252">
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</span></span><br>
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<font color="#ff0000"><i>What is a quantum particle?
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The dreams that stuff is made of!</i></font><br>
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<br>
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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"> </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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