2.1: Maxwell's Equations
- Page ID
- 44642
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Maxwell’s equations are given by
\[\vec{\nabla} \times \vec{H} = \vec{j} + \dfrac{\partial \vec{D}}{\partial t}, \nonumber \]
\[\vec{\nabla} \times \vec{E} = -\dfrac{\partial \vec{B}}{\partial t}, \label{eq2.1.2} \]
\[\vec{\nabla} \cdot \vec{D} = \rho, \nonumber \]
\[\vec{\nabla} \cdot \vec{B} = 0 \nonumber \].
The material equations accompanying Maxwell’s equations are:
\[\vec{D} = \epsilon_0 \vec{E} + \vec{P}, \nonumber \]
\[\vec{B} = \mu_0 \vec{H} + \vec{M}. \nonumber \]
Here, \(\vec{E}\) and \(\vec{H}\) are the electric and magnetic field, \(\vec{D}\) the dielectric flux, \(\vec{B}\) the magnetic flux, \(\vec{j}\) the current density of free carries, \(\rho\) is the free charge density, \(\vec{P}\) is the polarization, and \(\vec{M}\) the magnetization. By taking the curl of Equation \ref{eq2.1.2} and considering \(\vec{\nabla} \times (\vec{\nabla} \times \vec{E}) = \vec{\nabla} (\vec{\nabla} \vec{E}) - \Delta \vec{E}\), we obtain
\[\Delta \vec{E} - \mu_0 \dfrac{\partial}{\partial t} \left (\vec{j} + \epsilon_0 \dfrac{\partial \vec{E}}{\partial t} + \dfrac{\partial \vec{P}}{\partial t} \right ) = \dfrac{\partial}{\partial t} \vec{\nabla} \times \vec{M} + \vec{\nabla} (\vec{\nabla} \cdot \vec{E}) \nonumber \]
and hence
\[\left (\Delta - \dfrac{1}{c_0^2} \dfrac{\partial^2}{\partial t^2} \right ) \vec{E} = \mu_0 \left ( \dfrac{\partial vec{j}}{\partial t} + \dfrac{\partial^2}{\partial t^2} \vec{P} \right ) + \dfrac{\partial}{\partial t} \vec{\nabla} \times \vec{M} + \vec{\nabla} ( \vec{\nabla} \cdot \vec{E}).\label{eq2.1.8} \]
The vacuum velocity of light is
\[c_0 = \sqrt{\dfrac{1}{\mu_0 \epsilon_0}}. \nonumber \]