Update 2022-03-22 10:53
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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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<!-- 2022-03-15 Tue 08:10 -->
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<!-- 2022-03-22 Tue 10:52 -->
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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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@@ -1622,7 +1622,7 @@ implies the existence of magnetism, and vice-versa.
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<p>
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To illustrate this, we take a simple example
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</p>
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<aside id="orgbe19a87">
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<aside id="org964fb67">
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<p>
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See Purcell \& Morin, section 5.9.
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</p>
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@@ -1663,7 +1663,7 @@ The dilation factors in the test particle's frame are thus
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\gamma_\pm &= \frac{1}{\sqrt{1 - (v \mp u)^2/(c^2 \mp uv)^2}}
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= \frac{c^2 \mp uv}{\sqrt{(c^2 \mp uv)^2 - c^2 (v \mp u)^2}} \nonumber \\
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&= \frac{c^2 \mp uv}{\sqrt{(c^2 - v^2)(c^2 - u^2)}}
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= \gamma \frac{1 \mp uv/c^2}{\sqrt{q - u^2/c^2}}
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= \gamma \frac{1 \mp uv/c^2}{\sqrt{1 - u^2/c^2}}
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\end{align}
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<p>
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so the resultant line charge in the test frame is
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@@ -1680,25 +1680,25 @@ neutral in one reference frame, can appear to be charged in another.
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In the frame of the test particle, there is an electric field
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equal to that of a uniformly charged wire:
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\[
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E = \frac{\lambda_{\mbox{test}}}{2\pi \epsilon_0 s}
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E = \frac{\lambda_{\mbox{test}}}{2\pi \epsilon_0 r}
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\]
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so the force (in the test frame) is
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\[
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F_{\mbox{test}} = q E = -\frac{\lambda v}{\pi \epsilon_0 c^2 s} \frac{q u}{\sqrt{1 - u^2/c^2}}.
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F_{\mbox{test}} = q E = -\frac{\lambda v}{\pi \epsilon_0 c^2 r} \frac{q u}{\sqrt{1 - u^2/c^2}}.
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\]
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If there is a force on our test charge in this test frame, there must
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also be one in the lab frame. Using equation <a href="./red_rm_Mf.html#Ftr0">Ftr0</a>,
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\[
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F = \sqrt{1 - u^2/c^2} ~F_{\mbox{test}}
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= -\frac{\lambda v}{\pi \varepsilon_0 c^2} \frac{qu}{s}
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= -\frac{\lambda v}{\pi \varepsilon_0 c^2} \frac{qu}{r}
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\]
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which upon recognizing \(c^2 = \frac{1}{\varepsilon_0 \mu_0}\)
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and the current \(I = 2 \lambda v\) becomes
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\[
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F = - q u ~\frac{\mu_0 I}{2\pi s}
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F = - q u ~\frac{\mu_0 I}{2\pi r}
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\]
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which you will recognize as the magnetic part of the Lorentz force
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for a charge \(q\) moving at velocity \(v\) in the presence of the
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for a charge \(q\) moving at velocity \(u\) in the presence of the
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magnetic field of a long straight wire carrying current \(I\).
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</p>
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</div>
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@@ -1722,7 +1722,7 @@ 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: 2022-03-15 Tue 08:10</p>
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<p class="date">Created: 2022-03-22 Tue 10:52</p>
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<p class="validation"></p>
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</div>
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