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<!--replace-end-7--><!--replace-end-4--><!--replace-end-1--></head><body><div class="ui fluid container universe"><!--replace-start-2--><!--replace-start-3--><!--replace-start-6--><div class="ui text container" id="zettel-container" style="position: relative"><div class="zettel-view"><article class="ui raised attached segment zettel-content"><div class="pandoc"><h1 id="title-h1">Current</h1><blockquote><p>Electrical current is the movement of electrons from negatively charged atoms to positively charged atoms when an appropriate external force is applied.</p></blockquote><p>Current is the flow of electrons. Charge is the quantity that flows.</p><blockquote><p>The amount of current is the sum of the charges of the moving electrons past a given point.</p></blockquote><h2 id="why-current-exists">Why current exists</h2><p>Current exists because of the <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Coulombs Laws"><a href="Coulombs_Laws.html">first law of electrostatics</a></span></span>.</p><p>When there is an excess of electrons at one terminal (i.e. negatively charged atoms) and a deficiency of electrons at the other terminal (i.e. positively charged atoms), a <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Voltage"><a href="Voltage.html"><em>difference of potential</em></a></span></span> exists between the two terminals.</p><p>When the terminals are connected to each other via a conductor (e.g. copper wire) electrons will flow along the conductor. This is provided that there is a source to supply electrons at one end and remove them at the other. We call this force the <strong>voltage source</strong>.</p><p><em>The diagram below illustrates the flow of current where the circles are electrons knocking into each other and passing current:</em></p><p><img src="/static/charge-cylinder.svg" /></p><blockquote><p>Electrons travel very slowly through a conductor. This is in contrast to their intrinsic motion which of course equal to the speed of light (186, 000 miles per second).</p></blockquote><h2 id="formal-expression">Formal expression</h2><p>We measure <strong>charge</strong> in Coulombs (<span class="math inline">\(C\)</span>). A Coulomb is an aggregate of the charge of thousands of electrons because their individual charge is so small. One Coulomb is equal to the charge of <span class="math inline">\(6.24 \times 10 ^{18}\)</span> electrons.</p><p>We measure <strong>current</strong> in amps. When one coulomb of charge moves past a point in one second it is called an <strong>ampere</strong> (amp) represented as <span class="math inline">\(A\)</span>.</p><p>This relationship is captured in the following equation:</p><p><span class="math display">$$
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I = \frac{Q}{t}
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$$</span></p><ul><li><span class="math inline">\(I\)</span> = current measured in amps</li><li><span class="math inline">\(Q\)</span> = quantity of electrical charge measured in coulombs</li><li><span class="math inline">\(t\)</span> = time</li></ul><h3 id="application">Application</h3><p><em>Calculate the current in amps if 9 coulombs of charge flow past a point in an electric circuit in 3 seconds.</em></p><p><span class="math display">$$
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I = \frac{9}{3} \\
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I = 3 A
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$$</span></p><h2 id="direction-of-current">Direction of current</h2><p>In terms of the physics, current flows due to the movement of charged particles from atoms which are negatively charged to atoms which are positively charged. However when it comes to the representation of current in electrical circuits the convention is to view current as flowing from the positive to the negative terminal.</p><p>This is obviously physically inaccurate however it became the convention before electrons were properly understood when charge was thought to be a property of protons. So we are stuck with this convention in electronics.</p></div></article><nav class="ui attached segment deemphasized backlinksPane" id="neuron-backlinks-pane"><h3 class="ui header">Backlinks</h3><ul class="backlinks"><li><span class="zettel-link-container cf"><span class="zettel-link"><a href="Voltage.html">Voltage</a></span></span><ul class="context-list" style="zoom: 85%;"><li class="item"><div class="pandoc"><p>We noted in the discussion of <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Current"><a href="Current.html">current</a></span></span> that current flows when there is a difference of potential between two points with negatively charged atoms at one point and positively charged atoms at the other.</p></div></li></ul></li><li><span class="zettel-link-container cf"><span class="zettel-link"><a href="Ohms_Law.html">Ohm’s Law</a></span></span><ul class="context-list" style="zoom: 85%;"><li class="item"><div class="pandoc"><p>The relationship between <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Current"><a href="Current.html">current</a></span></span>, <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Voltage"><a href="Voltage.html">voltage</a></span></span>, and <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Resistance"><a href="Resistance.html">resistance</a></span></span> is defined by Ohm’s Law:</p></div></li></ul></li><li><span class="zettel-link-container cf"><span class="zettel-link"><a href="Electromagnetism.html">Electromagnetism</a></span></span><ul class="context-list" style="zoom: 85%;"><li class="item"><div class="pandoc"><p>Magnetism is a physical property produced by the <em>motion</em> of electric charge, which of course, is the same thing as <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Current"><a href="Current.html">electric current</a></span></span></p></div></li></ul></li><li><span class="zettel-link-container cf"><span class="zettel-link"><a href="DRAM_and_SRAM_memory.html">DRAM and SRAM memory</a></span></span><ul class="context-list" style="zoom: 85%;"><li class="item"><div class="pandoc"><p>However capacitors lose <span class="zettel-link-container cf"><span class="zettel-link" title="Zettel: Current"><a href="Current.html">charge</a></span></span> over time due to leaks. As a result DRAM is memory that needs to be refreshed (recharged) frequently. For this reason and because it only uses one transistor and capacitor per bit, DRAM is the less expensive form of volatile memory.</p></div></li></ul></li></ul></nav><nav class="ui attached segment deemphasized bottomPane" id="neuron-tags-pane"><div><span class="ui basic label zettel-tag" title="Tag">electricity</span><span class="ui basic label zettel-tag" title="Tag">physics</span></div></nav><nav class="ui bottom attached icon compact inverted menu blue" id="neuron-nav-bar"><!--replace-start-9--><!--replace-end-9--><a class="right item" href="impulse.html" title="Open Impulse"><i class="wave square icon"></i></a></nav></div></div><!--replace-end-6--><!--replace-end-3--><!--replace-end-2--><div class="ui center aligned container footer-version"><div class="ui tiny image"><a href="https://neuron.zettel.page"><img alt="logo" src="https://raw.githubusercontent.com/srid/neuron/master/assets/neuron.svg" title="Generated by Neuron 1.9.35.3" /></a></div></div></div></body></html> |