Update 2022-02-08 17:21
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<!-- 2022-02-08 Tue 06:55 -->
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<!-- 2022-02-08 Tue 17:21 -->
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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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@@ -272,6 +272,10 @@ Table of contents
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</summary>
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<ul>
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<li>
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<a href="./in_t_l.html#in_t_l">Section and equation labelling</a><span class="headline-id">in.t.l</span>
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</li>
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<li>
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<a href="./in_t_c.html#in_t_c">Contextual colors</a><span class="headline-id">in.t.c</span>
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</li>
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@@ -736,7 +740,7 @@ Table of contents
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</li>
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<li>
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<a href="./emsm_esm_d.html#emsm_esm_d">Dielectrics</a><span class="headline-id">emsm.esm.d</span>
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<a href="./emsm_esm_di.html#emsm_esm_di">Dielectrics</a><span class="headline-id">emsm.esm.di</span>
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</li>
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<li>
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@@ -1622,7 +1626,7 @@ Table of contents
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<p>
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Since \({\boldsymbol \nabla} \cdot {\bf B} = 0\) in magnetostatics, following Helmholtz's theorem we can write
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</p>
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<div class="core div" id="org8c7f863">
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<div class="core div" id="org8d029d6">
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<p>
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\[
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{\bf B} = {\boldsymbol \nabla} \times {\bf A}
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@@ -1644,7 +1648,7 @@ add any curlless function (so gradient of a scalar field) to the vector potentia
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without changing the magnetic field. This is called a {\bf gauge choice} in electrodynamics.
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For example, we can {\bf always} eliminate the divergence of \({\bf A}\),
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</p>
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<div class="main div" id="orga7d7df6">
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<div class="main div" id="org2f5ec71">
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<p>
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{\bf Example gauge choice:}
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\[
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@@ -1675,7 +1679,7 @@ zero at infinity,
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<p>
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Under this gauge choice, Ampère's law becomes
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</p>
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<div class="main div" id="org59fd103">
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<div class="main div" id="orga1e23e0">
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<p>
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\[
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{\boldsymbol \nabla}^2 {\bf A} = -\mu_0 {\bf J}
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@@ -1688,7 +1692,7 @@ Under this gauge choice, Ampère's law becomes
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Note: this is a Poisson equation for each component.
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For currents falling off sufficiently rapidly at infinity,
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</p>
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<div class="core div" id="orgb880c5e">
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<div class="core div" id="org4174f16">
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<p>
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\[
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{\bf A} ({\bf r}) = \frac{\mu_0}{4\pi} \int d\tau' \frac{J({\bf r}')}{|{\bf r} - {\bf r}'|}
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@@ -1700,7 +1704,7 @@ For currents falling off sufficiently rapidly at infinity,
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<p>
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For line and surface currents, <i>(beware Griffiths' <b>horrendous</b> notation)</i>
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</p>
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<div class="main div" id="org3d2b3ad">
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<div class="main div" id="org712334e">
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<p>
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\[
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{\bf A}({\bf r}) = \frac{\mu_0}{4\pi} \int dl' \frac{{\bf I ({\bf r}')}}{|{\bf r} - {\bf r}'|},
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@@ -1714,7 +1718,7 @@ For line and surface currents, <i>(beware Griffiths' <b>horrendous</b> notation)
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<div class="example div" id="org05a3ec0">
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<div class="example div" id="org0baf51b">
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<p>
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\paragraph{Example 5.11:} a spherical shell of radius \(R\), carrying a uniform surface charge
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\(\sigma\), is set spinning at angular velocity \(\omega\). Find the vector potential at \({\bf r}\).
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@@ -1728,7 +1732,7 @@ the sphere is uniform !
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</div>
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<div class="example div" id="org238fce0">
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<div class="example div" id="org1f6ff4e">
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<p>
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\paragraph{Example 5.12:} find the vector potential of an infinite solenoid with \(n\) turns
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pet unit length, radius \(R\) and current \(I\).
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@@ -1788,7 +1792,7 @@ For an 'amperian' loop outside, the flux is always \(\mu_0 n I (\pi R^2)\), so
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<hr><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: 2022-02-08 Tue 06:55</p>
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<p class="date">Created: 2022-02-08 Tue 17:21</p>
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<p class="validation"><a href="https://validator.w3.org/check?uri=referer">Validate</a></p>
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</div>
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