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373 lines
14 KiB
HTML
373 lines
14 KiB
HTML
<!DOCTYPE html>
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<html lang="en"><!-- #BeginTemplate "/Templates/Advanced.dwt" --><!-- DW6 -->
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<!-- Mirrored from www.mathsisfun.com/physics/electromagnetic-spectrum.html by HTTrack Website Copier/3.x [XR&CO'2014], Sat, 29 Oct 2022 00:51:03 GMT -->
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<!-- #BeginEditable "doctitle" -->
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<title>Electromagnetic Spectrum</title>
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<meta name="description" content="Electricity and magnetism are linked in an ongoing dance, and we call it electromagnetism.">
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<script>reSpell=[["meters","metres"],["nanometers","nanometres"],["micrometers","micrometres"],["centimeters","centimetres"],["color","colour"],["ionization","ionisation"],["ionizing","ionising"]];</script>
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<div id="adTop"></div>
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<div id="hdr"></div>
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<div id="tran"></div>
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<div id="adHide"></div>
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<div id="cookOK"></div>
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<article id="content" role="main">
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<!-- #BeginEditable "Body" -->
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<h1 class="center">Electromagnetic Spectrum</h1>
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<h2>Electromagnetism</h2>
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<p>It is called "electromagnetism" because electricity and magnetism are linked:</p>
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<p class="center"><img src="images/electro-magnetic-field-prop.svg" alt="electro magnetic field properties" height="170" width="414"><br>
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A changing <b>electric</b> field produces a <b>magnetic</b> field,<br>
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a changing <b>magnetic</b> field produces an <b>electric</b> field,<br>
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<br>
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<img src="images/changing-electro-magnetic.svg" alt="changing electric vs magnetic field" height="115" width="191"> <br>
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<br>
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... around and around ... !</p>
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<p>So electricity and magnetism are linked in an ongoing dance.</p>
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<p>This effect heads off through space at the fastest speed possible: the <b>speed of light</b>.</p>
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<p>Here is the full <b>electromagnetic spectrum</b>:</p>
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<div class="script" style="height: 260px;">
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images/em-spectrum.js
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</div>
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<p> </p>
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<p><b>Higher frequency</b> (rate of vibration) has <b>more energy</b> and shorter wavelength.</p>
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<p>The spectrum is continuous with no sudden changes or boundaries.</p>
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<p>How a wave interacts with matter depends on its <b>energy</b> and the type of matter</p>
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<div class="example">
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<h3>Example: Our Bodies</h3>
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<ul>
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<li>radio waves pass through our bodies</li>
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<li>some microwaves get absorbed and heat us up</li>
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<li>skin absorbs some infrared and light, and reflects the rest<br>
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<img src="images/sun-feet.jpg" alt="sun feet" height="182" width="480"></li>
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<li>UV (ultraviolet) is absorbed by the very outer layer of our skin (which causes sunburn and skin cancer)</li>
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<li>X-rays are absorbed at different rates by bone and muscle so we can see inside us<br>
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<img src="images/x-ray-hand.jpg" alt="x ray hand" height="170" width="300"></li>
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<li>Gamma rays mostly pass through, but any that get absorbed may harm our cells by ionization (see below)</li>
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</ul>
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<p>So some waves pass right through our bodies, others get reflected or absorbed at different rates.</p>
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</div>
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<div class="example">
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<p style="float:right; margin: 0 0 5px 10px;"><img src="../measure/images/sun-dog.jpg" alt="sun dog" height="255" width="156"></p>
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<h3>Example: From The Sun</h3>
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<p>A lot of the the radiation from the Sun gets <b>reflected</b> or <b>absorbed</b> by the atmosphere.</p>
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<p>Only</p>
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<ul>
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<li>radio</li>
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<li>some infrared</li>
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<li>visible light, and</li>
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<li>some ultraviolet</li>
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</ul>
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<p>get all the way through:</p>
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<p><img src="images/electromagnetic-spectrum-block.svg" alt="electromagnetic spectrum block vs pass" height="342" width="1283"></p>
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<p>Imagine: if our eyes could only see X-rays the sky would be black!</p>
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<p class="center"><img src="images/nustar-x-ray-telescope.jpg" alt="nustar x ray telescope" height="192" width="300"><br>
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So telescopes like the NuSTAR X-ray telescope have to be in orbit.</p>
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</div>
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<h2>Ranges</h2>
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<p>We like to think of the spectrum as having these ranges:</p>
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<ul>
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<li><a href="waves-radio-microwave.html">Radio and Microwaves</a> have low frequencies, <b>low energy</b> and long wavelengths</li>
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<li><a href="infrared.html">IR (infrared)</a></li>
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<li><a href="light.html">Visible Light</a></li>
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<li><a href="ultraviolet.html">UV (ultraviolet)</a> </li>
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<li><a href="x-rays-gamma.html">X-rays and Gamma rays</a> have high frequencies, <b>high energy</b> and short wavelengths</li>
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</ul>
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<p>There is disagreement on the exact range values (for example X-Rays from an X-ray tube and Gamma rays from radioactive materials overlap) but here is a handy guide:</p>
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<div class="simple">
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<table style="border: 0; margin:auto;">
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<tbody>
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<tr>
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<th> </th>
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<th width="20"> </th>
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<th>Typical Wavelength</th>
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<th width="20"> </th>
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<th>Commonly Defined Range</th>
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</tr>
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<tr>
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<td>Radio</td>
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<td> </td>
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<td>meters (m)</td>
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<td> </td>
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<td>Above 10 cm</td>
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</tr>
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<tr>
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<td>Microwave</td>
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<td> </td>
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<td>centimeters (cm)</td>
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<td> </td>
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<td>1 mm to 10 cm</td>
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</tr>
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<tr>
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<td>Infrared</td>
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<td> </td>
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<td>micrometers (μm)</td>
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<td> </td>
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<td>750 nm to 1 mm</td>
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</tr>
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<tr>
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<td>Light</td>
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<td> </td>
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<td>100s of nanometers</td>
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<td> </td>
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<td> 380 nm to 750 nm</td>
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</tr>
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<tr>
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<td>UV</td>
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<td> </td>
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<td>100 nanometers</td>
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<td> </td>
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<td> 10 nm to 380 nm</td>
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</tr>
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<tr>
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<td>X-rays</td>
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<td> </td>
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<td>nanometers (nm)</td>
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<td> </td>
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<td> 10 pm to 10 nm</td>
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</tr>
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<tr>
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<td>Gamma rays</td>
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<td> </td>
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<td> picometers (pm)</td>
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<td> </td>
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<td>below 10 pm</td>
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</tr>
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</tbody></table>
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</div>
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<p>See <span class="center"><a href="units-equations.html">Units in Equations</a></span> for more about nanometers, picometers, etc.</p>
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<h2>Speed of Light</h2>
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<p><span class="center">Electromagnetic</span> waves travel at the "Speed of Light" at almost <b>300,000,000 meters per second</b> (to be exact: 299,792,458 meters per second) <b>in a vacuum</b>.</p>
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<p>That is <b>300 million meters</b> every second, or:</p>
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<ul>
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<li>3 × 10<sup>8</sup> m/s</li>
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<li>300,000 km/s</li>
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<li>186,000 miles per second</li>
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</ul>
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<p>But the speed can be slower ...</p>
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<div class="simple">
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<table style="border: 0; margin:auto;">
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<tbody>
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<tr>
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<th>Medium</th>
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<th align="center"><b>Speed</b><br>
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million m/s</th>
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</tr>
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<tr>
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<td>Vacuum</td>
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<td style="text-align:center;">300</td>
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</tr>
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<tr>
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<td>Ice</td>
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<td style="text-align:center;">228</td>
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</tr>
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<tr>
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<td>Water</td>
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<td style="text-align:center;">225</td>
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</tr>
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<tr>
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<td>Ethanol</td>
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<td style="text-align:center;">220</td>
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</tr>
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<tr>
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<td>Glass</td>
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<td style="text-align:center;">205</td>
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</tr>
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<tr>
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<td>Olive oil</td>
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<td style="text-align:center;">204</td>
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</tr>
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<tr>
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<td>Diamond</td>
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<td style="text-align:center;">123</td>
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</tr>
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</tbody></table>
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</div>
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<p>At slower speeds the wavelength is <b>shorter</b> for the same frequency.</p>
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<p>We can work out the wavelength:</p>
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<p class="center large">wavelength = <span class="intbl"><em>speed</em><strong>frequency</strong></span></p>
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<div class="example">
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<h3>Example: Red Light at a frequency of 4 × 10<sup>14</sup></h3>
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<p>In a <b>vacuum</b> the wavelength is:</p>
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<p class="center larger"><span class="intbl"><em>3 × 10<sup>8</sup></em><strong>4 × 10<sup>14</sup></strong></span> = 7.5 × 10<sup>-7</sup> = 750 nm</p>
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<p>In <b>water</b> the wavelength is:</p>
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<p class="center larger"><span class="intbl"><em>2.25 × 10<sup>8</sup></em><strong>4 × 10<sup>14</sup></strong></span> = 5.625 × 10<sup>-7</sup> = 562 nm</p>
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<p>The wavelength is different but the <b>light stays the same color</b> as the frequency is the same.</p>
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</div>
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<div class="def">
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<p><b>Important</b>: the wavelengths mentioned on this page are for a <b> vacuum</b>. Adjust them like above if not.</p>
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</div>
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<p>
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Try adjusting the sliders on this demo and see how the top of a wave moves the same speed (which is actually billions of times slower than reality):</p>
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<div class="script" style="height: 350px;">
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../algebra/images/wave-sine.js?mode=light
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</div>
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<div class="example">
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<h3><span class="center">Wavelengths</span> vs <span class="center">Frequency</span> Activity</h3>
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<p>Try this:
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Walk across the room in <b>5 seconds</b>:</p>
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<ul>
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<li>taking long steps ("long wavelength")</li>
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<li>and again taking short steps ("short wavelength")</li>
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</ul>
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<p>What is the <b>frequency</b> of your steps in each case?</p>
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<p>Now try that again but take <b>20 seconds</b> to cross the room. What happens?</p>
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</div>
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<h2>Energy</h2>
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<p>A higher frequency (rate of vibration) has shorter wavelength and more energy.</p>
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<div class="example">
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<h3>Example: Which has more energy, light or X-rays?</h3>
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<p>X-rays have more energy, with frequencies around 10<sup>18</sup>, compared to light around 10<sup>14</sup></p>
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</div>
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<div class="example">
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<h3>Example: Which has more energy, red light or blue light?</h3>
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<p>Blue light has higher frequency (with shorter wavelengths), so has <b>more energy than red</b>.</p>
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<p class="center"><img src="images/light-red-blue.svg" alt="light red:lower energy, blue:higher energy" height="245" width="338"><br></p>
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</div>
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<p> </p>
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<p style="float:right; margin: 0 0 5px 10px;"><img src="images/ionizing-atom2.svg" alt="ionizing atom" height="195" width="293"></p>
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<h2>Energy and Ionization</h2>
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<p> </p>
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<p><b>Gamma rays, x-rays, and some ultraviolet waves have such high energy that they are "ionizing," meaning they can knock electrons out of atoms.</b></p>
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<p> </p>
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<p>This makes atoms charged and more likely to form new chemical reactions, which can be harmful to our cells, killing them or changing them so they grow out of control and form cancer.</p>
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<h2>Remembering</h2>
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<div class="fun">
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<h3>How to remember the spectrum?</h3>
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<p>It goes: <b>Radio, Micro, Infrared, Light, Ultraviolet, Rays</b></p>
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<ul>
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<li>Radio and Microwaves are at the low energy end </li>
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<li>Infrared is "before red"</li>
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<li>Visible light goes "Roy G Bv": <b>R</b>ed <b>O</b>range <b>Y</b>ellow <b>G</b>reen <b>B</b>lue <b>V</b>iolet</li>
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<li>Ultraviolet is "after violet"</li>
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<li>Rays (X-rays and gamma rays) at the high energy end</li>
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</ul>
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<p>To remember the energy and <b>danger</b> levels, think:</p>
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<p class="center"> <i>"Radio is low, but rays are like razors"</i></p>
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</div>
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<h2><span class="center">As Photons</span></h2>
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<p><span class="center">Electromagnetic</span> radiation behaves as waves, but also behaves as packets of energy called <b>Photons</b>.</p>
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<ul>
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<li>We can measure a photon's position and momentum.</li>
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<li>Photons have no mass, but each photon has a specific amount of energy that depends on its frequency (number of vibrations per second).</li>
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<li>Each photon has a wavelength</li>
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</ul>
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<p>So it is like a particle and also like a wave. This is called the "wave–particle duality".</p>
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<p style="float:left; margin: 0 10px 5px 0;"><img src="images/einstein.jpg" alt="einstein" height="217" width="200"></p>
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<p> </p>
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<p>Einstein wrote about it:</p>
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<p><i>"It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either."</i></p>
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