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157 lines
7.2 KiB
HTML
157 lines
7.2 KiB
HTML
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<title>Reflection</title>
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<div id="hdr"></div>
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<div id="logo"><a href="../index.html"><img src="../images/style/logo.svg" alt="Math is Fun"></a></div>
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<div id="advText">Advanced</div>
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<div id="content" role="main">
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<!-- #BeginEditable "Body" -->
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<h1 class="center">Reflection</h1>
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<p>Waves bounce off a surface at the <b>same angle</b> they strike it:</p>
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<p class="center"><img src="images/reflection.svg" alt="reflection: incident ray and reflected ray matching angle" /></p>
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<p class="large center">Angle In Matches Angle Out</p>
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<p>Or in more mathematical language:</p>
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<div class="def">
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<p class="center"><span class="large">Angle of Incidence = Angle of Reflection</span><br>
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<i>The Law of Reflection</i></p>
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</div>
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<p>Another example:</p>
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<p class="large center"><img src="images/reflection2.svg" alt="reflection: incident ray and reflected ray matching angle" /></p>
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<div class="words"><p style="float:right; margin: 0 0 5px 10px;"><img src="../geometry/images/normal.svg" alt="normal" /></p>
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<p> </p>
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<p>The <b>Normal</b> is the direction directly away from the surface (at <a href="../rightangle.html">right angles</a> to it).</p>
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</div>
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<p>Angles are measured from the Normal.</p>
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<h2>Mirror</h2>
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<p>Here we see light bouncing off a mirror to create a "virtual image" that looks like the real thing (but reversed):</p>
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<p class="center"><img src="images/reflection-mirror.svg" alt="reflection mirror makes virtual image" /><br>
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Our puppy sees someone in the mirror.</p>
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<h2>Curved Mirrors</h2>
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<p>What happens when light reflects off a curved surface? We can draw individual <b>rays of light</b> to find out!</p>
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<p>Here is how to work out the reflection of a ray:</p>
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<table style="border: 0;">
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<tr>
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<td width="33%" align="center"><img src="images/normal-a.svg" alt="normal on curve" /></td>
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<td width="33%" align="center"><img src="images/normal-b.svg" alt="normal on curve and right angle" /></td>
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<td width="33%" align="center"><img src="images/normal-c.svg" alt="normal on curve and matching angles" /></td>
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</tr>
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<tr>
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<td width="33%" align="center"><b>Where the ray hits</b> draw a line <b>flat against the curve</b><br>
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(called a <a href="../geometry/tangent-secant-lines.html">tangent line</a>)</td>
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<td width="33%" align="center"> The normal line is at <b><br>
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right angles</b> to<br>
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that tangent line</td>
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<td width="33%" align="center"><b>Angle in matches angle out</b><br>
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either side of the normal line</td>
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</tr>
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</table>
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<p>And we get this:</p>
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<p class="center"><img src="images/reflection-mirror-curved.svg" alt="reflection mirror curved makes upside down virtual image" /><br>
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Our puppy sees an upside down reflection!</p>
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<p class="center">Just like the inside of this spoon:<br>
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<img src="images/spoon-reflection.jpg" width="178" height="242" alt="spoon reflection" /></p>
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<p>And what about this wonderful shape:</p>
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<p class="center"><img src="images/cloud-gate.jpg" width="428" height="193" alt="cloud gate reflection" /><br>
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<i>Cloud Gate</i> in Chicago<br></p>
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<h2>Parabola</h2>
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<p>The <a href="../geometry/parabola.html">parabola</a> is a special curved shape that takes any ray coming directly in and sends it to a single "focus" point:</p>
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<p class="center"><img src="../geometry/images/parabola-reflector.svg" alt="parabola" /></p>
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<p>This is useful for telescopes. They can have a large parabolic collection area that sends the radiation to one small detector.</p>
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<p class="center"><img src="images/james-webb.jpg" width="360" height="272" alt="james webb reflection" /><br>
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Technicians stand in front of one segment of the James Webb Telescope's<br>
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"segmented parabolic reflector"</p>
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<p class="center"><img src="images/telescope-bure-plateau.jpg" width="360" height="234" alt="telescope bure plateau" /><br>
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Incoming radio waves get sent to the focal point for detection.<i><br>
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Plateau de Bore Radio Telescope</i></p>
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<h2>Ellipse</h2>
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<p>For an <a href="../geometry/ellipse.html">ellipse</a>, light or sound starting at one focus point reflects to the other focus point:</p>
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<p class="center"><img src="../geometry/images/ellipse-focus.svg" alt="ellipse focus points" /></p>
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<p class="center larger">Have a play with a simple <a href="../geometry/ellipse-reflect-model.html">computer model of reflection inside an ellipse</a>.</p>
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<h2>Echo</h2>
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<p class="words">An <b>echo</b> is a reflection, usually of sound from a hard surface.</p>
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<p class="center"><img src="images/echo-clap.svg" alt="echo clap" /><br>
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As well as hearing it directly, the sound of this clap<br>
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is also heard a short while later from the wall</p>
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<div style="clear:both"></div>
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<p>Other types of waves can have echoes, such as radio waves.</p>
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<p> </p>
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<div class="questions">
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<script>getQ(3346, 17687, 17691, 17693, 5152, 12552, 17695, 17698, 12548, 17697);</script> </div>
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<div class="related">
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<a href="index.html">Physics Index</a>
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Copyright © 2020 MathsIsFun.com
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