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<!DOCTYPE html PUBLIC "-//w3c//dtd html 4.0 transitional//en">
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<meta name="Author" content="C. L. Davis">
<title>Light and Optics - Polarisation - Physics 299</title>
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<body style="color: rgb(0, 0, 0); background-color: rgb(255, 255,
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<center>
<h1><img src="ULPhys1.gif" align="texttop" height="50" width="189">
</h1>
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<center>
<h1>Polarisation</h1>
</center>
<center><img src="celticbar.gif" height="22" width="576"> <br>
<br>
<font color="#ff0000"><i>"</i></font><font color="#ff0000"><i>
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</i></font>
<div style="overflow: hidden; color: rgb(0, 0, 0);
background-color: rgb(255, 255, 255); text-align: left;
text-decoration: none; border: medium none; position: absolute;
left: -99999px;" id="r1PostCPBlock">A physicist is just an
atom's way of looking at itself.<br>
<span>Read more at <a style="color: #003399;"
href="http://www.brainyquote.com/quotes/quotes/n/nielsbohr382329.html#urRTQl9BfaJk3yj3.99">http://www.brainyquote.com/quotes/quotes/n/nielsbohr382329.html#urRTQl9BfaJk3yj3.99</a></span></div>
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charset=windows-1252">
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<div style="overflow: hidden; color: rgb(0, 0, 0);
background-color: rgb(255, 255, 255); text-align: left;
text-decoration: none; border: medium none; position: absolute;
left: -99999px;" id="r1PostCPBlock">A physicist is just an
atom's way of looking at itself.<br>
<span>Read more at <a style="color: #003399;"
href="http://www.brainyquote.com/quotes/quotes/n/nielsbohr382329.html#urRTQl9BfaJk3yj3.99">http://www.brainyquote.com/quotes/quotes/n/nielsbohr382329.html#urRTQl9BfaJk3yj3.99</a></span></div>
<font color="#ff0000"><i>
<meta http-equiv="content-type" content="text/html;
charset=windows-1252">
</i></font>
<div style="overflow: hidden; color: rgb(0, 0, 0);
background-color: rgb(255, 255, 255); text-align: left;
text-decoration: none; border: medium none; position: absolute;
left: -99999px;" id="r1PostCPBlock">A physicist is just an
atom's way of looking at itself.<br>
<span>Read more at <a style="color: #003399;"
href="http://www.brainyquote.com/quotes/quotes/n/nielsbohr382329.html#urRTQl9BfaJk3yj3.99">http://www.brainyquote.com/quotes/quotes/n/nielsbohr382329.html#urRTQl9BfaJk3yj3.99</a></span></div>
<font color="#ff0000"><i>A physicist is just an atom's way of
looking at itself" </i></font><br>
Niels Bohr<br>
</center>
<img src="netbar.gif" align="middle" height="40" width="100%"> <br>
<br>
<ul>
<li>We have seen that electromagnetic waves may be described by
transverse waves of <b>E</b> and <b>B</b> (at right angles to
each other).&nbsp; However, there is nothing special about any
particular direction for the <b>E</b> or <b>B</b> vectors to
oscillate.&nbsp; In fact an <b>unpolarised</b> wave contains
waves with <b>E</b> vectors in all possible directions (for
each <b>E</b> wave there is a <b>B</b> wave at right
angles).&nbsp; If the wave propagates in the z direction this
wave has <b>E</b> components in all possible directions.</li>
</ul>
<ul>
<li>In a polarised wave the <b>E</b> vector oscillates in a
specific direction - the direction of polarisation.</li>
</ul>
<div align="left">
<ul>
<li>Polarised light does not appear any different to unpolarised
light to our eyes.&nbsp; The difference only becomes apparent
when observing through transparent polarising material,</li>
</ul>
<div align="center"><img alt="polarisation fig1"
src="lo_polarisation1.jpg" height="218" width="500">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<img alt="polarisation fig2" src="lo_polarisation2.gif"
height="190" width="423"><br>
<br>
<div align="left">
<ul>
<li>The intensity of initially unpolarised light which
passes through two polarisers is given by <a
href="http://micro.magnet.fsu.edu/optics/timeline/people/malus.html"><img
alt="malus" src="lo_malus.jpg" align="middle"
border="0" height="128" width="94"></a><a
href="http://www.physicshandbook.com/laws/maluslaw.htm">Malus'
Law,</a></li>
</ul>
<div align="center"><img alt="polarisation eqn1"
src="lo_polarisation_eqn1.jpg" height="56" width="141"><br>
<blockquote>
<div align="left">where I<sub>0</sub> is the incident
intensity and &#952; is the angle between the directions of
the two polarisers.&nbsp; Note that for "cross
polarisers" there is no transmitted wave.<br>
</div>
</blockquote>
<div align="left">
<ul>
<li><img alt="hot" src="hot.gif" align="middle"
height="43" width="79">&nbsp; Analog TV and radio
signals are transmitted as polarised waves.&nbsp; When
rotating the direction of an antenna you are
effectively rotating the second polariser, thus
varying the angle &#952;.&nbsp; Maximum and minimum signal
reception will be obtained with orientations of the
antenna at ninety degrees to each other.<br>
</li>
</ul>
</div>
<blockquote>
<div align="left"> </div>
</blockquote>
</div>
</div>
</div>
</div>
<br>
<img src="netbar.gif" height="40" width="100%"><br>
<center>"<span style="font-style: italic; color: rgb(255, 0, 0);">Alimony
is like buying hay for a dead horse"</span><br>
Groucho Marx<br>
<br>
<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>
<p><img src="header-index.gif" height="51" width="92"> </p>
</center>
<p><br>
</p>
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