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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@@ -1666,7 +1666,7 @@ so we get
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Substituting this in \ref{Gr(8.6)} and using the divergence theorem,
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we obtain
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</p>
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<div class="main div" id="org1ad9e6b">
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<div class="main div" id="org9d063a8">
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<p>
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{\bf Poynting's theorem}
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\[
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@@ -1691,7 +1691,7 @@ energy is carried by EM fields out of \({\cal V}\) across its boundary surface.
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<p>
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Energy per unit time, per unit area carried by EM fields:
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</p>
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<div class="core div" id="org97f8866">
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<div class="core div" id="org91d3725">
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<p>
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{\bf Poynting vector}
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\[
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@@ -1704,7 +1704,7 @@ Energy per unit time, per unit area carried by EM fields:
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<p>
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We can thus express Poynting's theorem more compactly:
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</p>
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<div class="core div" id="orgc096fa3">
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<div class="core div" id="org5a2fb1e">
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<p>
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{\bf Poynting's theorem}
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\[
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@@ -1717,7 +1717,7 @@ We can thus express Poynting's theorem more compactly:
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<p>
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where we have defined the total
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</p>
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<div class="core div" id="org56f314c">
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<div class="core div" id="orgf2b55fe">
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<p>
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{\bf Energy in electromagnetic fields}
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\[
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@@ -1740,7 +1740,7 @@ Then,
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\]
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so we get the
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</p>
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<div class="core div" id="orgd477ba8">
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<div class="core div" id="orgb8783a7">
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<p>
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{\bf Poynting theorem (differential form)}
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\[
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@@ -1757,7 +1757,7 @@ and has a similar for to the continuity equation
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<div class="example div" id="orgf36d646">
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<div class="example div" id="orgc6f817f">
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<p>
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\paragraph{Example 8.1} Current in a wire: Joule heating. Energy per unit time delivered to wire: from Poynting.
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Assuming that the field is uniform, the electric field parallel to the wire is
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@@ -1767,11 +1767,11 @@ Assuming that the field is uniform, the electric field parallel to the wire is
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where \(V\) is the potential difference between the ends ald \(L\) is the length. Magnetic field is circumferential:
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wire of radius \(a\),
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\[
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{\boldsymbol B} = \frac{\mu_0 I}{2\pi a} \hat{\boldsymbol \phi}
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{\boldsymbol B} = \frac{\mu_0 I}{2\pi a} \hat{\boldsymbol \varphi}
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\]
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Poynting:
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\[
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{\boldsymbol S} = \frac{1}{\mu_0} \frac{V}{L} \frac{\mu_0 I}{2\pi a} \hat{\boldsymbol x} \times \hat{\boldsymbol \phi} = -\frac{VI}{2\pi a L} \hat{\boldsymbol s}
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{\boldsymbol S} = \frac{1}{\mu_0} \frac{V}{L} \frac{\mu_0 I}{2\pi a} \hat{\boldsymbol x} \times \hat{\boldsymbol \varphi} = -\frac{VI}{2\pi a L} \hat{\boldsymbol s}
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\]
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and points radially inwards. Energy per unit time passing surface of wire:
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\[
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@@ -1802,7 +1802,7 @@ 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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