From 16555851b6514a736c5c9d8e73de7da7fc9b6288 Mon Sep 17 00:00:00 2001 From: Prefetch Date: Thu, 20 Oct 2022 18:25:31 +0200 Subject: Migrate from 'jekyll-katex' to 'kramdown-math-sskatex' --- source/know/concept/magnetic-field/index.md | 68 ++++++++++++++--------------- 1 file changed, 34 insertions(+), 34 deletions(-) (limited to 'source/know/concept/magnetic-field') diff --git a/source/know/concept/magnetic-field/index.md b/source/know/concept/magnetic-field/index.md index 369c8a6..8d215fb 100644 --- a/source/know/concept/magnetic-field/index.md +++ b/source/know/concept/magnetic-field/index.md @@ -8,28 +8,28 @@ categories: layout: "concept" --- -The **magnetic field** $\vb{B}$ is a vector field +The **magnetic field** $$\vb{B}$$ is a vector field that describes magnetic effects, and is defined as the field that correctly predicts the [Lorentz force](/know/concept/lorentz-force/) -on a particle with electric charge $q$: +on a particle with electric charge $$q$$: $$\begin{aligned} \vb{F} = q \vb{v} \cross \vb{B} \end{aligned}$$ -If an object is placed in a magnetic field $\vb{B}$, +If an object is placed in a magnetic field $$\vb{B}$$, and wants to rotate to align itself with the field, -then its **magnetic dipole moment** $\vb{m}$ -is defined from the aligning torque $\vb{\tau}$: +then its **magnetic dipole moment** $$\vb{m}$$ +is defined from the aligning torque $$\vb{\tau}$$: $$\begin{aligned} \vb{\tau} = \vb{m} \times \vb{B} \end{aligned}$$ -Where $\vb{m}$ has units of $\mathrm{J / T}$. -From this, the **magnetization** $\vb{M}$ is defined as follows, +Where $$\vb{m}$$ has units of $$\mathrm{J / T}$$. +From this, the **magnetization** $$\vb{M}$$ is defined as follows, and roughly represents the moments per unit volume: $$\begin{aligned} @@ -38,17 +38,17 @@ $$\begin{aligned} \vb{m} = \int_V \vb{M} \dd{V} \end{aligned}$$ -If $\vb{M}$ has the same magnitude and orientation throughout the body, -then $\vb{m} = \vb{M} V$, where $V$ is the volume. -Therefore, $\vb{M}$ has units of $\mathrm{A / m}$. +If $$\vb{M}$$ has the same magnitude and orientation throughout the body, +then $$\vb{m} = \vb{M} V$$, where $$V$$ is the volume. +Therefore, $$\vb{M}$$ has units of $$\mathrm{A / m}$$. -A nonzero $\vb{M}$ complicates things, +A nonzero $$\vb{M}$$ complicates things, since it contributes to the field -and hence modifies $\vb{B}$. +and hence modifies $$\vb{B}$$. We thus define -the "free" **auxiliary field** $\vb{H}$ -from the "bound" field $\vb{M}$ -and the "net" field $\vb{B}$: +the "free" **auxiliary field** $$\vb{H}$$ +from the "bound" field $$\vb{M}$$ +and the "net" field $$\vb{B}$$: $$\begin{aligned} \vb{H} \equiv \frac{1}{\mu_0} \vb{B} - \vb{M} @@ -56,24 +56,24 @@ $$\begin{aligned} \vb{B} = \mu_0 (\vb{H} + \vb{M}) \end{aligned}$$ -Where the **magnetic permeability of free space** $\mu_0$ is a known constant. +Where the **magnetic permeability of free space** $$\mu_0$$ is a known constant. It is important to point out some inconsistencies here: -$\vb{B}$ contains a factor of $\mu_0$, and thus measures **flux density**, -while $\vb{H}$ and $\vb{M}$ do not contain $\mu_0$, +$$\vb{B}$$ contains a factor of $$\mu_0$$, and thus measures **flux density**, +while $$\vb{H}$$ and $$\vb{M}$$ do not contain $$\mu_0$$, and therefore measure **field intensity**. Note that this convention is the opposite of the analogous [electric fields](/know/concept/electric-field/) -$\vb{E}$, $\vb{D}$ and $\vb{P}$. -Also note that $\vb{P}$ has the opposite sign convention of $\vb{M}$. +$$\vb{E}$$, $$\vb{D}$$ and $$\vb{P}$$. +Also note that $$\vb{P}$$ has the opposite sign convention of $$\vb{M}$$. Some objects, called **ferromagnets** or **permanent magnets**, -have an inherently nonzero $\vb{M}$. -Others objects, when placed in a $\vb{B}$-field, -may instead gain an induced $\vb{M}$. +have an inherently nonzero $$\vb{M}$$. +Others objects, when placed in a $$\vb{B}$$-field, +may instead gain an induced $$\vb{M}$$. -When $\vb{M}$ is induced, +When $$\vb{M}$$ is induced, its magnitude is usually proportional -to the applied field strength $\vb{H}$: +to the applied field strength $$\vb{H}$$: $$\begin{aligned} \vb{B} @@ -83,20 +83,20 @@ $$\begin{aligned} = \mu \vb{H} \end{aligned}$$ -Where $\chi_m$ is the **volume magnetic susceptibility**, -and $\mu_r \equiv 1 + \chi_m$ and $\mu \equiv \mu_r \mu_0$ are +Where $$\chi_m$$ is the **volume magnetic susceptibility**, +and $$\mu_r \equiv 1 + \chi_m$$ and $$\mu \equiv \mu_r \mu_0$$ are the **relative permeability** and **absolute permeability** of the medium, respectively. Materials with intrinsic magnetization, i.e. ferromagnets, -do not have a well-defined $\chi_m$. +do not have a well-defined $$\chi_m$$. -If $\chi_m > 0$, the medium is **paramagnetic**, -meaning it strengthens the net field $\vb{B}$. -Otherwise, if $\chi_m < 0$, the medium is **diamagnetic**, -meaning it counteracts the applied field $\vb{H}$. +If $$\chi_m > 0$$, the medium is **paramagnetic**, +meaning it strengthens the net field $$\vb{B}$$. +Otherwise, if $$\chi_m < 0$$, the medium is **diamagnetic**, +meaning it counteracts the applied field $$\vb{H}$$. -For $|\chi_m| \ll 1$, as is often the case, -the magnetization $\vb{M}$ can be approximated by: +For $$|\chi_m| \ll 1$$, as is often the case, +the magnetization $$\vb{M}$$ can be approximated by: $$\begin{aligned} \vb{M} -- cgit v1.2.3