Update 2022-02-14 20:42
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<!-- 2022-02-13 Sun 21:20 -->
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<!-- 2022-02-14 Mon 20:35 -->
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<meta charset="utf-8">
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<meta name="viewport" content="width=device-width, initial-scale=1">
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<title>Pre-Quantum Electrodynamics</title>
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@@ -1598,16 +1598,31 @@ Table of contents
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</svg></a><span class="headline-id">ems.ca.me.md</span></h5>
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<div class="outline-text-5" id="text-ems_ca_me_md">
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<p>
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The series (\ref{Gr(3.95)}) is organized in increasing powers of inverse distance.
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The leading term is called the {\bf monopole} term, and is
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The series <a href="./ems_ca_me_a.html#p_Leg">p_Leg</a> is organized in increasing powers of inverse distance.
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The leading term is called the *monopole term, and is
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</p>
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<div class="core div" id="org0dea0f3">
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<div class="eqlabel" id="org4619ff2">
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<p>
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<a id="p_mono"></a><a href="./ems_ca_me_md.html#p_mono"><svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="currentColor" class="bi bi-link" viewBox="0 0 16 16">
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<path d="M6.354 5.5H4a3 3 0 0 0 0 6h3a3 3 0 0 0 2.83-4H9c-.086 0-.17.01-.25.031A2 2 0 0 1 7 10.5H4a2 2 0 1 1 0-4h1.535c.218-.376.495-.714.82-1z"/>
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<path d="M9 5.5a3 3 0 0 0-2.83 4h1.098A2 2 0 0 1 9 6.5h3a2 2 0 1 1 0 4h-1.535a4.02 4.02 0 0 1-.82 1H12a3 3 0 1 0 0-6H9z"/>
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</svg></a>
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</p>
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<div class="alteqlabels" id="org5a3bf3c">
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<ul class="org-ul">
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<li>Gr (3.97)</li>
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</ul>
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</div>
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</div>
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<div class="core div" id="org333d379">
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<p>
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\[
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V_{\mbox{\tiny mono}} ({\bf r}) = \frac{1}{4\pi \varepsilon_0} \frac{Q}{r}, \hspace{1cm}
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Q = \int_{\cal V} d\tau_s \rho({\bf r}_s).
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\label{Gr(3.97)}
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\]
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\phi_m ({\bf r}) = \frac{1}{4\pi \varepsilon_0} \frac{Q}{r}, \hspace{1cm}
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Q = \int_{\cal \phi} d\tau_s \rho({\bf r}_s).
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\tag{p_mono}\label{p_mono}
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\]
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</p>
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</div>
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@@ -1616,25 +1631,38 @@ For a point charge, the monopole term gives the exact potential.
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</p>
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<p>
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The next term is the {\bf dipole} term: by using \(P_1 (x) = x\), we have
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The next term is the <b>dipole</b> term: by using \(P_1 (x) = x\), we have
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\[
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V_{\mbox{\tiny di}} ({\bf r}) = \frac{1}{4\pi \varepsilon_0} \frac{1}{r^2} \int_{\cal V} d\tau_s \hat{\bf r} \cdot {\bf r}_s \rho({\bf r}_s)
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\phi_d ({\bf r}) = \frac{1}{4\pi \varepsilon_0} \frac{1}{r^2} \int_{\cal V} d\tau_s \hat{\bf r} \cdot {\bf r}_s \rho({\bf r}_s)
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\]
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This can be written
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</p>
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<div class="core div" id="orga21233c">
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<div class="eqlabel" id="org82b714c">
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<p>
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<a id="p_di"></a><a href="./ems_ca_me_md.html#p_di"><svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="currentColor" class="bi bi-link" viewBox="0 0 16 16">
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<path d="M6.354 5.5H4a3 3 0 0 0 0 6h3a3 3 0 0 0 2.83-4H9c-.086 0-.17.01-.25.031A2 2 0 0 1 7 10.5H4a2 2 0 1 1 0-4h1.535c.218-.376.495-.714.82-1z"/>
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<path d="M9 5.5a3 3 0 0 0-2.83 4h1.098A2 2 0 0 1 9 6.5h3a2 2 0 1 1 0 4h-1.535a4.02 4.02 0 0 1-.82 1H12a3 3 0 1 0 0-6H9z"/>
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</svg></a>
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</p>
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<div class="alteqlabels" id="org0d44254">
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</div>
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</div>
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<div class="core div" id="org0634724">
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<p>
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\[
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V_{\mbox{\tiny di}} ({\bf r}) = \frac{1}{4\pi \varepsilon_0} \frac{\hat{\bf r} \cdot {\bf p}}{r^2},
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\hspace{10mm}{\bf p} \equiv \int_{\cal V} d\tau_s ~{\bf r}_s ~\rho({\bf r}_s).
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\label{eq:electric_dipole}
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\]
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\phi_d ({\bf r}) = \frac{1}{4\pi \varepsilon_0} \frac{\hat{\bf r} \cdot {\bf p}}{r^2},
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\hspace{10mm}{\bf p} \equiv \int_{\cal V} d\tau_s ~{\bf r}_s ~\rho({\bf r}_s).
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\tag{p_di}\label{p_di}
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\]
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</p>
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</div>
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<p>
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in terms of the {\bf dipole moment} \({\bf p}\).
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Note that the dipole moment is an internal property of the source charges, and that it
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in terms of the <b>dipole moment</b> \({\bf p}\).
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Note that the dipole moment is a property related to the internal distribution
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of the source charges, and that it
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in general depends on the chosen point of origin (more on this later).
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</p>
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@@ -1643,7 +1671,11 @@ Since dipole moments are vectors, they are summed following vector addition rule
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</p>
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<p>
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{\bf Pure dipole:} two charges closer and closer together, but charges higher and higher such that \({\bf p}\) remains finite.
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In the literature, one comes across the notion of a <b>mathematical dipole</b> or
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synonymously a <b>pure dipole</b>: this is simply an abstraction in which the charges
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are moved infinitesimally close together, while their charges are proportionally
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increased such that the dipole moment remains the same. In such cases, the
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multipole expansion terminates at the dipole term.
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</p>
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</div>
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</div>
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@@ -1651,6 +1683,7 @@ Since dipole moments are vectors, they are summed following vector addition rule
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<br><ul class="navigation-links"><li>Prev: <a href="ems_ca_me_a.html">Approximate Potential at Large Distance <small>[ems.ca.me.a]</small></a></li><li>Next: <a href="ems_ca_me_h.html">Higher Moments <small>[ems.ca.me.h]</small></a></li><li>Up: <a href="ems_ca_me.html">The Multipole Expansion <small>[ems.ca.me]</small></a></li></ul>
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<br>
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<hr>
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@@ -1666,7 +1699,7 @@ target="_blank">Creative Commons Attribution 4.0 International License</a>.
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</div>
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<div id="postamble" class="status">
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<p class="author">Author: Jean-Sébastien Caux</p>
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<p class="date">Created: 2022-02-13 Sun 21:20</p>
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<p class="date">Created: 2022-02-14 Mon 20:35</p>
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<p class="validation"></p>
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</div>
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