SherbyNet - /page/wikibook/entry.mu

Micron Document

<!DOCTYPE html>

<title>Point source</title>

</head>

<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Point source</span></span>

</h1>

</header>

/* start https://en.wikipedia.org/ */

.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}

/* end https://en.wikipedia.org/ */

</style><div role="note" class="hatnote navigation-not-searchable">For other uses, see <a href="Point_source_(disambiguation)" class="mw-disambig" title="Point source (disambiguation)">Point source (disambiguation)</a>.</div>

/* start https://en.wikipedia.org/ */

.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}

/* end https://en.wikipedia.org/ */

</style>

<p>A <b>point source</b> is a single identifiable <i>localized</i> source of something. A point source has a negligible extent, distinguishing it from other source geometries. Sources are called point sources because, in <a href="Mathematical_model" title="Mathematical model">mathematical modeling</a>, these sources can usually be approximated as a mathematical <a href="Point_(geometry)" title="Point (geometry)">point</a> to simplify analysis.

</p><p>The actual source need not be physically small if its size is negligible relative to other length scales in the problem. For example, in <a href="Astronomy" title="Astronomy">astronomy</a>, <a href="Star" title="Star">stars</a> are routinely treated as point sources, even though they are in actuality much larger than the <a href="Earth" title="Earth">Earth</a>.

</p><p>In <a href="Three-dimensional_space" title="Three-dimensional space">three dimensions</a>, the density of something leaving a point source decreases in proportion to the <a href="Inverse_square" class="mw-redirect" title="Inverse square">inverse square</a> of the <a href="Distance" title="Distance">distance</a> from the source, if the distribution is <a href="Isotropic" class="mw-redirect" title="Isotropic">isotropic</a>, and there is no <a href="Absorption_(electromagnetic_radiation)" title="Absorption (electromagnetic radiation)">absorption</a> or other loss.

</p>

<div class="mw-heading mw-heading2"><h2 id="Mathematics">Mathematics</h2></div>

<p>In mathematics, a <b>point source</b> is a <a href="Mathematical_singularity" class="mw-redirect" title="Mathematical singularity">singularity</a> from which <a href="Flux" title="Flux">flux</a> or flow is emanating. Although singularities such as this do not exist in the observable universe, mathematical point sources are often used as approximations to reality in <a href="Physics" title="Physics">physics</a> and other fields.

</p>

<div class="mw-heading mw-heading2"><h2 id="Visible_electromagnetic_radiation_(light)">Visible electromagnetic radiation (light)</h2></div>

<p>Generally, a <a href="Light_source" class="mw-redirect" title="Light source">source of light</a> can be considered a point source if the resolution of the imaging instrument is too low to resolve the source's apparent size. There are two types and sources of light: a point source and an extended source.

</p><p>Mathematically an object may be considered a point source if its <a href="Angular_resolution" title="Angular resolution">angular size</a>, <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \theta }">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle \theta }</annotation>

</semantics>

</math></span><img src="./6e5ab2664b422d53eb0c7df3b87e1360d75ad9af.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.09ex; height:2.176ex;" alt="{\displaystyle \theta }" loading="lazy"></span>, is much smaller than the resolving power of the telescope:<br>

</mrow>

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle \theta <<\lambda /D}</annotation>

</semantics>

</math></span><img src="./befe60234306edbe96d24f7052511859994dfb52.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:10.439ex; height:2.843ex;" alt="{\displaystyle \theta <<\lambda /D}" loading="lazy"></span>,<br> where <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \lambda }">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle \lambda }</annotation>

</semantics>

</math></span><img src="./b43d0ea3c9c025af1be9128e62a18fa74bedda2a.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.355ex; height:2.176ex;" alt="{\displaystyle \lambda }" loading="lazy"></span> is the wavelength of light and <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle D}">

</mstyle>

</mrow>

<annotation encoding="application/x-tex">{\displaystyle D}</annotation>

</semantics>

</math></span><img src="./f34a0c600395e5d4345287e21fb26efd386990e6.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.924ex; height:2.176ex;" alt="{\displaystyle D}" loading="lazy"></span> is the telescope diameter.

</p><p>Examples:

</p>

<ul><li>Light from a distant star seen through a small telescope</li>

<li>Light passing through a <a href="Pinhole" class="mw-redirect" title="Pinhole">pinhole</a> or other small <a href="Aperture" title="Aperture">aperture</a>, viewed from a distance much greater than the size of the hole</li>

<li>Light from a <a href="Street_light" title="Street light">street light</a> in a large-scale study of <a href="Light_pollution" title="Light pollution">light pollution</a> or street <a href="Lighting" title="Lighting">illumination</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="Other_electromagnetic_radiation">Other electromagnetic radiation</h2></div>

<p><a href="Radio_wave" title="Radio wave">Radio wave</a> sources that are smaller than one radio <a href="Wavelength" title="Wavelength">wavelength</a> are also generally treated as point sources. Radio emissions generated by a fixed electrical circuit are usually <a href="Polarization_(waves)" title="Polarization (waves)">polarized</a>, producing <a href="Anisotropic" class="mw-redirect" title="Anisotropic">anisotropic</a> radiation. If the propagating medium is lossless, however, the radiant power in the radio waves at a given distance will still vary as the inverse square of the distance if the angle remains constant to the source polarization.

</p><p><a href="Gamma_ray" title="Gamma ray">Gamma ray</a> and <a href="X-ray" title="X-ray">X-ray</a> sources may be treated as a point source if sufficiently small. <a href="Radiological_contamination" class="mw-redirect" title="Radiological contamination">Radiological contamination</a> and nuclear sources are often point sources. This has significance in <a href="Health_physics" title="Health physics">health physics</a> and <a href="Radiation_protection" title="Radiation protection">radiation protection</a>.

</p><p>Examples:

</p>

<ul><li><a href="Antenna_(radio)" title="Antenna (radio)">Radio antennas</a> are often smaller than one wavelength, even though they are many meters across</li>

<li><a href="Pulsars" class="mw-redirect" title="Pulsars">Pulsars</a> are treated as point sources when observed using <a href="Radio_telescopes" class="mw-redirect" title="Radio telescopes">radio telescopes</a></li>

<li>In nuclear physics, a "hot spot" is a point source of <a href="Radiation" title="Radiation">radiation</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="Sound">Sound</h2></div>

<p><a href="Sound" title="Sound">Sound</a> is an oscillating <a href="Pressure" title="Pressure">pressure</a> wave. As the pressure oscillates up and down, an audio point source acts in turn as a fluid point source and then a fluid point sink. (Such an object does not exist physically, but is often a good simplified model for calculations.)

</p><p>Examples:

</p>

<ul><li><a href="Seismology" title="Seismology">Seismic vibration</a> from a localised seismic experiment searching for oil</li>

<li><a href="Noise_pollution" title="Noise pollution">Noise pollution</a> from a <a href="Jet_engine" title="Jet engine">jet engine</a> in a large-scale study of noise pollution</li>

<li>A <a href="Loudspeaker" title="Loudspeaker">loudspeaker</a> may be considered as a point source in a study of the <a href="Acoustics" title="Acoustics">acoustics</a> of <a href="Airport" title="Airport">airport</a> announcements</li></ul>

<p>A <a href="Coaxial_loudspeaker" title="Coaxial loudspeaker">coaxial loudspeaker</a> is designed to work as a point source to allow a wider field for listening.

</p>

<div class="mw-heading mw-heading2"><h2 id="Ionizing_radiation">Ionizing radiation</h2></div>

<p>Point sources are used as a means of calibrating <a href="Ionizing_radiation" title="Ionizing radiation">ionizing radiation</a> instruments. They are usually sealed capsules and are most commonly used for gamma, x-ray and beta-measuring instruments.

</p>

<p>In <a href="Vacuum" title="Vacuum">a vacuum</a>, heat escapes as <a href="Radiation" title="Radiation">radiation</a> isotropically. If the source remains stationary in a <a href="Compressible_fluid" class="mw-redirect" title="Compressible fluid">compressible fluid</a> such as <a href="Air" class="mw-redirect" title="Air">air</a>, flow patterns can form around the source due to <a href="Convection" title="Convection">convection</a>, leading to an <a href="Anisotropy" title="Anisotropy">anisotropic</a> pattern of heat loss. The most common form of anisotropy is the formation of a thermal <a href="Plume_(hydrodynamics)" class="mw-redirect" title="Plume (hydrodynamics)">plume</a> above the heat source.

Examples:

</p>

<ul><li>Geological hotspots on the surface of the Earth which lie at the tops of thermal plumes rising from deep inside the Earth</li>

<li>Plumes of heat studied in <a href="Thermal_pollution" title="Thermal pollution">thermal pollution</a> tracking.</li></ul>

<div class="mw-heading mw-heading2"><h2 id="Fluid">Fluid</h2></div>

<p>Fluid point sources are commonly used in <a href="Fluid_dynamics" title="Fluid dynamics">fluid dynamics</a> and <a href="Aerodynamics" title="Aerodynamics">aerodynamics</a>. A point source of fluid is the inverse of a fluid point sink (a point where fluid is removed). Whereas fluid sinks exhibit complex rapidly changing behavior such as is seen in <a href="Vortex" title="Vortex">vortices</a> (for example water running into a plug-hole or <a href="Tornado" title="Tornado">tornadoes</a> generated at points where air is rising), fluid sources generally produce simple flow patterns, with stationary isotropic point sources generating an expanding sphere of new fluid. If the fluid is moving (such as wind in air or currents in water) a <a href="Plume_(hydrodynamics)" class="mw-redirect" title="Plume (hydrodynamics)">plume</a> is generated from the point source.

</p><p>Examples:

</p>

<ul><li><a href="Air_pollution" title="Air pollution">Air pollution</a> from a <a href="Power_plant" class="mw-redirect" title="Power plant">power plant</a> <a href="Flue_gas_stack" class="mw-redirect" title="Flue gas stack">flue gas stack</a> in a large-scale analysis of air pollution</li>

<li><a href="Water_pollution" title="Water pollution">Water pollution</a> from an <a href="Oil_refinery" title="Oil refinery">oil refinery</a> <a href="Wastewater" title="Wastewater">wastewater</a> discharge outlet in a large-scale analysis of water pollution</li>

<li>Gas escaping from a pressurized pipe in a laboratory</li>

<li>Smoke is often released from point sources in a <a href="Wind_tunnel" title="Wind tunnel">wind tunnel</a> in order to create a <a href="Plume_(hydrodynamics)" class="mw-redirect" title="Plume (hydrodynamics)">plume</a> of smoke which highlights the flow of the wind over an object</li>

<li>Smoke from a localized chemical fire can be blown in the wind to form a <a href="Plume_(hydrodynamics)" class="mw-redirect" title="Plume (hydrodynamics)">plume</a> of pollution</li></ul>

<div class="mw-heading mw-heading2"><h2 id="Pollution">Pollution</h2></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Point_source_pollution" title="Point source pollution">Point source pollution</a></div>

<p>Sources of various types of pollution are often considered as point sources in large-scale studies of pollution.<sup id="cite_ref-noaa_point_1-0" class="reference"><a href="#cite_note-noaa_point-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

</p>

<ul><li><a href="Line_source" title="Line source">Line source</a></li>

<li><a href="Dirac_delta_function" title="Dirac delta function">Dirac delta function</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

/* start https://en.wikipedia.org/ */

.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}

/* end https://en.wikipedia.org/ */

</style><div class="reflist">

/* start https://en.wikipedia.org/ */

.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("./mw/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("./mw/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("./mw/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("./mw/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}

/* end https://en.wikipedia.org/ */

</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://oceanservice.noaa.gov/education/kits/pollution/03pointsource.html">"Categories of Pollution: Point Source"</a>. <i>oceanservice.noaa.gov/</i>. NOAA<span class="reference-accessdate">. Retrieved <span class="nowrap">13 September</span> 2014</span>.</cite></span>

</li>

</ol></div></div></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2025-03-03" href="https://en.wikipedia.org/wiki/?title=Point_source&oldid=1278619590">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

</div>

</div></div>

</div>

</main>

</div>

</body></html>