121 lines
5.8 KiB
HTML
121 lines
5.8 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" 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>Light and Optics - Total Internal Reflection - Physics 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);" 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>Total Internal Reflection</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>"One machine can do the work of fifty
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ordinary men. No machine can do the work of one
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extraordinary man"</i></font><br>
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Elbert Hubbard<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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<ul>
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<li>When light passes from a medium with refractive index n<sub>1</sub>
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to a medium with refractive index n<sub>2</sub>, where n<sub> 1</sub>
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> n<sub>2</sub>, if the incident angle is greater than some
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critical angle <img alt="" src="lo_tir_eqn1.gif" style="width:
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17px; height: 24px;" align="middle">, the light will undergo <i>
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total internal reflection</i> (TIR).</li>
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<br>
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<li>The diagram below represents a light source underwater with
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light rays striking the water-air interface. Rays 1, 2 and
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3 are refracted at the interface according to Snell's law, the
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refracted ray bending away from the normal such that <img
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alt="" src="lo_tir_eqn3.gif" style="width: 19px; height:
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23px;" align="middle"> > <img alt=""
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src="lo_tir_eqn2.gif" style="width: 16px; height: 23px;"
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align="middle"> . When <img alt="" src="lo_tir_eqn3.gif"
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style="width: 19px; height: 23px;" align="middle"> = 90<sup>o</sup>
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the refracted ray is directed along the surface of the water and
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<img alt="" src="lo_tir_eqn2.gif" style="width: 16px; height:
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23px;" align="middle"> is called the critical angle <img
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alt="" src="lo_tir_eqn1.gif" style="width: 17px; height:
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24px;" align="middle">. For incident angles greater than
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<img alt="" src="lo_tir_eqn1.gif" style="width: 17px; height:
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24px;" align="middle"> there is no refracted ray, the light
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undergoes <i>total internal reflection</i> back into the water.</li>
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</ul>
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<blockquote><img alt="exclamation" src="exclamation-icon.gif"
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height="30" width="31"> Note that even when TIR does not take
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place there will always be a reflected wave (back into the water),
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in this case, of low intensity (about 4% of the total energy is
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reflected). In other words, at an interface where the
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incident angle is less than the critical angle, part of the
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incident energy is transmitted and part is reflected.<br>
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</blockquote>
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<ul>
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<br>
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<img alt="confused smiley" src="confused_smiley.gif" height="22"
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width="15"> Even though all the light energy undergoes
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total internal reflection, there is a "disturbance" in the other
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medium (air in the example above) called the evanescent wave which
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travels along the interface between the two media...<br>
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<div align="center"><img
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src="lo_internalreflectiontwodiagrams.jpg" alt="TIR"
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align="middle" height="235" width="570"> <br>
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</div>
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<li> At the critical angle<br>
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<div align="center"><b><img alt="" src="lo_tir_eqn4.gif"
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style="width: 131px; height: 89px;"> <br>
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</b></div>
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<br>
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For light passing into air from water the critical angle
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is equal to about 49<sup>o</sup>. </li>
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<br>
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<li>Thus a fish-eye's view is of the world in a 98<sup>o</sup>
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cone. Outside this cone all is darkness...[Actually this
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is not true due to the scattering of light in water] <br>
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<div align="center"><img src="lo_coneofdarknessforfish.jpg"
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alt="Fish view" align="middle" height="291" width="363"> <br>
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</div>
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</li>
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<br>
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<li> Total Internal Reflection is the mechanism by which fibre
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optic cables work. Signal losses along such cables is
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extremely small since <i><b> ALL</b></i> the incident energy is
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reflected. <br>
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<br>
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<div align="center"><img
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src="lo_fiberopticcladdingandfiberbundle.jpg" alt="Fibre
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Optic" align="middle" height="185" width="570"> </div>
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</li>
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</ul>
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<img src="netbar.gif" height="40" width="100%">
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<center><span style="font-weight: normal; font-style: italic; color:
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rgb(255, 0, 0);">"I know that this defies the law of gravity,
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but, you see, I never studied</span><span style="font-style:
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italic; color: rgb(255, 0, 0);"> law."</span><span style=""><br>
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</span>Bugs Bunny <br>
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<br>
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<img src="celticbar.gif" height="22" width="576"></center>
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<center> <br>
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<i style="font-weight: normal;">Dr. C. L. Davis</i> <br>
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<i style="font-weight: normal;">Physics Department</i> <br>
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<i style="font-weight: normal;">University of Louisville</i> <br>
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<i style="font-weight: normal;">email</i><span style="font-weight:
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normal;">: </span><a style="font-weight: normal;"
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href="mailto:c.l.davis@louisville.edu">c.l.davis@louisville.edu</a><span
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style="font-weight: normal;"> </span><br>
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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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