Update 2022-02-14 20:42
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@@ -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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<!-- 2022-02-13 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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@@ -1608,7 +1608,7 @@ For a single dipole: refer to \ref{Gr(5.83)} (vector potential of single dipole
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For a chunk of material with local magnetization \({\bf M} ({\bf r})\),
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by the principle of superposition we thus have:
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</p>
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<div class="main div" id="org86bd6f7">
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<div class="main div" id="org362b749">
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<p>
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\[
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{\bf A} ({\bf r}) = \frac{\mu_0}{4\pi} \int_{\cal V} d\tau' ~\frac{{\bf M} ({\bf r}') \times ({\bf r} - {\bf r}')}{|{\bf r} - {\bf r}'|^3}
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@@ -1650,7 +1650,7 @@ Problem 1.61 b) (p.56): leads to
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\]
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Reinterpretation: first term: potential from volume current,
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</p>
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<div class="main div" id="org2d491ac">
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<div class="main div" id="orgfe22f72">
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<p>
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\[
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{\bf J}_b = {\boldsymbol \nabla} \times {\bf M}
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@@ -1662,7 +1662,7 @@ Reinterpretation: first term: potential from volume current,
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<p>
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second term: potential from surface current,
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</p>
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<div class="main div" id="org67395f8">
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<div class="main div" id="org2d7aeed">
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<p>
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\[
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{\bf K}_b = {\bf M} \times \hat{\bf n}
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@@ -1674,7 +1674,7 @@ second term: potential from surface current,
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<p>
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With these definitions,
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</p>
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<div class="main div" id="org2145099">
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<div class="main div" id="org19936af">
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<p>
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\[
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{\bf A} ({\bf r}) = \frac{\mu_0}{4\pi} ∫_{\cal V} dτ' \frac{{\bf J}_b ({\bf r}')}{|{\bf r} - {\bf r}'|}
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@@ -1695,18 +1695,18 @@ in the volume and surface of the material.
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<div class="example div" id="org6d7ec15">
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<div class="example div" id="org9fe198f">
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<p>
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\paragraph{Example 6.1:} find field of uniformly magnetized sphere.
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\paragraph{Solution:} put z axis along \({\bf M}\).
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\[
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{\bf J}_b = {\boldsymbol \nabla} \times {\bf M} = 0,
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\hspace{1cm}
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{\bf K}_b = {\bf M} \times \hat{\bf n} = M \sin \theta \hat{\boldsymbol \phi}.
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{\bf K}_b = {\bf M} \times \hat{\bf n} = M \sin \theta \hat{\boldsymbol \varphi}.
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\]
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Rotating spherical shell of uniform surface charge \(\sigma\): surface current density
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\[
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{\bf K} = \sigma {\bf v} = \sigma \omega R \sin \theta \hat{\boldsymbol \phi}.
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{\bf K} = \sigma {\bf v} = \sigma \omega R \sin \theta \hat{\boldsymbol \varphi}.
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\]
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Same if \(\sigma R {\boldsymbol \omega} = {\bf M}\). Refer to Example 5.11,% ({\it not done in class !}),
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\[
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@@ -1741,7 +1741,7 @@ 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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