Update 2022-03-02 15:47
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-11
@@ -1,7 +1,7 @@
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<!-- 2022-03-01 Tue 08:14 -->
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<!-- 2022-03-02 Wed 15:45 -->
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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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@@ -1626,7 +1626,7 @@ Let's consider the spatial function in the potential for a single point source c
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\[
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\frac{1}{|{\bf r} - {\bf r}_s|}
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\]
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How does this look when we're at large distances \(|{\bf r}| \gg |{\bf r}_s|\) ?
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How does this look when we're at large distances \(|{\bf r}| \gg |{\bf r}_s|\)?
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We can formally expand this in powers of \(|{\bf r}_s|/|{\bf r}|\). For simplicity, let's start by
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putting \({\bf r} = r ~\hat{\bf z}, r > 0\) and \({\bf r}_s = r_s \hat{\bf z}\), with \(|r_s| < r\).
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By Taylor expanding, we get
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@@ -1636,14 +1636,14 @@ By Taylor expanding, we get
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Formally, we could do this for any vector \({\bf r}_s\) such that \(|{\bf r}_s| < |{\bf r}|\) by
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Taylor expanding with the \({\boldsymbol \nabla}\) operator,
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</p>
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<div class="eqlabel" id="org522710d">
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<div class="eqlabel" id="orgbba2c7c">
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<p>
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<a id="1or_grad"></a><a href="./ems_ca_me_a.html#1or_grad"><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="org3aaf125">
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<div class="alteqlabels" id="orgba8e23d">
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</div>
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@@ -1661,14 +1661,14 @@ the potential takes the form of the general solution of Laplace's equation <a hr
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Reading the parameters, we get \(A_l = 0\), \(B_l = r_s^l\). Putting back a generic angle
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(the coefficients remain the same), we thus get
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</p>
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<div class="eqlabel" id="org22f2df1">
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<div class="eqlabel" id="org50a8092">
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<p>
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<a id="1or_Leg"></a><a href="./ems_ca_me_a.html#1or_Leg"><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="org555af0c">
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<div class="alteqlabels" id="org6a1a9bb">
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<ul class="org-ul">
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<li>Gr(3.94)</li>
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</ul>
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@@ -1690,14 +1690,14 @@ we can expand the potential at a point \({\bf r}\) outside \({\cal V}\) accordin
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(here, we put the origin of our coordinate system closer to all points in \({\cal V}\) than to \({\bf r}\)
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to ensure convergence)
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</p>
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<div class="eqlabel" id="org64fa160">
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<div class="eqlabel" id="orgcf8de8f">
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<p>
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<a id="p_Leg"></a><a href="./ems_ca_me_a.html#p_Leg"><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="org33b5b72">
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<div class="alteqlabels" id="org09dcc77">
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<ul class="org-ul">
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<li>Gr (3.95)</li>
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</ul>
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@@ -1760,14 +1760,14 @@ For \(r \gg d\), we can expand (immediately dropping terms of order \(d^2/r^2\))
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Putting things together, the leading term in the expansion <a href="./ems_ca_me_a.html#p_Leg">p_Leg</a> for the
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potential of the physical dipole is given by
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</p>
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<div class="eqlabel" id="org99e07b3">
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<div class="eqlabel" id="org5950916">
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<p>
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<a id="p_physdi"></a><a href="./ems_ca_me_a.html#p_physdi"><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="org0f12ac7">
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<div class="alteqlabels" id="org1ac0511">
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<ul class="org-ul">
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<li>Gr (3.90)</li>
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</ul>
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@@ -1814,7 +1814,7 @@ 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: 2022-03-01 Tue 08:14</p>
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<p class="date">Created: 2022-03-02 Wed 15:45</p>
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<p class="validation"></p>
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</div>
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