182 lines
7.6 KiB
HTML
182 lines
7.6 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>Magnetism - Force Between Parallel Wires: Ampere Definition -
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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,
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255);" link="#0000ee" vlink="#551a8b" alink="#ff0000">
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<center>
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<h1> <img src="ULPhys1.gif" height="50" width="189"
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align="texttop"></h1>
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</center>
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<center>
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<h1>Force Between Two Parallel Wires: Ampere Definition <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>
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<meta http-equiv="content-type" content="text/html;
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charset=windows-1252">
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</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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</i></font>
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<div class="copy-paste-block"><font color="#ff0000"><i><span
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class="bqQuoteLink">"A</span></i></font><font
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color="#ff0000"><i><span class="bqQuoteLink"> fact is a simple
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statement that everyone believes. It is innocent,
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unless found guilty. A hypothesis is a novel
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suggestion that no one wants to believe. It is
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guilty, until found effective</span></i><span></span>"</font><br>
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</div>
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<font color="#ff0000"><i> </i><font color="#000000">Edward Teller</font></font><br>
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</center>
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<img src="netbar.gif" height="40" width="100%" align="middle">
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<blockquote> </blockquote>
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<ul>
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<li> We have just seen that a long straight wire carrying current
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i<sub>1</sub> produces a <b>B</b> field which forms
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concentric circles around the wire whose magnitude a distance
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"d" from the wire is given by <br>
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</li>
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</ul>
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<div align="center"><img alt="magforce2wireseqn1"
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src="mag_force_2wires_eqn1.jpg" height="73" width="108"><br>
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<blockquote>
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<div align="left">with direction given by "the" right-hand-rule.<br>
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</div>
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</blockquote>
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<div align="left">
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<ul>
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<li><img alt="magforce2wiresfig1"
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src="mag_force_2wires_fig1.jpg" height="340" width="245"
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align="right">If a second parallel wire carrying a current
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i<sub>2</sub> is placed a distance "d" from the first, it
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will feel a force due to the presense of <b>B<sub>1</sub> </b>.
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The force felt by a length l<sub>2</sub> of this
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second wire is</li>
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</ul>
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<div align="center"><img alt="magforce2wireseqn2"
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src="mag_force_2wires_eqn2.jpg" height="32" width="149"><br>
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<blockquote>
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<div align="left">so that<br>
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<div align="center"><img alt="magforce2wireseqn3"
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src="mag_force_2wires_eqn3.jpg" height="69"
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width="144"><br>
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<br>
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<div align="left">with a direction such that i<sub>2</sub>
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is attracted towards i<sub>1</sub> as shown at right.<br>
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Then the force per unit length on i<sub>2</sub> is
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given by<br>
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<div align="center"><img alt="magforce2wireseqn4"
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src="mag_force_2wires_eqn4.jpg" height="76"
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width="119"><br>
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</div>
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</div>
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</div>
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</div>
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</blockquote>
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<div align="left">
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<div align="center">
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<div align="left">
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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"> Note that if we reverse
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the roles of i<sub>1</sub> and i<sub>2</sub> we
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obtain the same expression for F<sub>1</sub>/l<sub>1</sub>
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. That is, i<sub>1</sub> exerts a force
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on i<sub>2</sub> and i<sub>2</sub>
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exerts an equal, but opposite, force on i<sub>1</sub>
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as expected from Newton's Third Law ("Action equals
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Reaction").</li>
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</ul>
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<ul>
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<li>The above analysis applies for parallel currents -
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the two wires are attracted to each other. If
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one of the currents is reversed, so that the
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currents are "anti-parallel", the force per unit
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length is unchanged, but the force acting on each
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wire is reversed. In other words the wires are
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now repelled from each other.</li>
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</ul>
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<blockquote><img alt="exclamation"
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src="exclamation-icon.gif" height="30" width="31"> <i><b>"Like
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currents are attractive, unlike currents are
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repelled"</b></i>. Note that this is
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opposite to the behavior of point electric charges.<br>
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<br>
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</blockquote>
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<ul>
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<li><big><big><font color="#cc33cc"><u><i><b>Definition
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of the Ampere</b></i></u></font></big></big></li>
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</ul>
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<blockquote>
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<p>The unit of electric current, the Ampere, is
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defined using the force between parallel wires
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carrying current.<br>
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</p>
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<p align="center"><img alt="tick" src="tickred1.gif"
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height="48" width="48"><big><i><b>"The Ampere is
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that current which when flowing in two
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infinite parallel wires</b></i><i><b> one
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metre apart produces a force between them of 2
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x 10</b></i><i><b><sup>-7</sup></b></i><i><b>
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N/m"</b></i><i><b> </b></i></big><br>
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<br>
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</p>
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<p align="left">Proof:<br>
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</p>
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<div align="center"><img alt="magforce2wireseqn5"
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src="mag_force_2wires_eqn5.jpg" height="71"
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width="479"></div>
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</blockquote>
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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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<img src="netbar.gif" height="40" width="100%">
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<div align="center">
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<div align="center"> </div>
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<center>
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<p style="color: rgb(255, 0, 0); font-style: italic;"
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class="MsoNormal">
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<meta http-equiv="content-type" content="text/html;
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charset=windows-1252">
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</p>
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<font color="#ff0000"><i>What do you call a dinosaur with an
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extensive vocabulary ? A thesaurus. </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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<blockquote> </blockquote>
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</div>
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</body>
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</html>
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