[Physics] Varying electric field

electromagnetism

Maybe a silly question, but anyway:

We always hear about "electromagnetic induction", that is when a time varying magnetic flux induces an electric field.

Does the same thing happen when there is a varying electric field?
Does a time varying electric field result in an induced magnetic field?

Best Answer

Yes varying electric field induce a magnetic field as stated by the Maxwell's fourth equation (an extension of the Ampère's law). In free space that is: $$ \nabla\times\vec{B}=\mu_0\vec{J}+\mu_0\epsilon_0\frac{\partial\vec{E}}{\partial t} $$ An example can be any type of electromagnetic wave, where $\vec{E}$ (and also $\vec{B}$) is varying with time, a simple one would be a plane-wave where $\vec{E}=\vec{E}_0\cos(\omega t-kz)$ with $\vec{E}_0$ is a costant vector (more here).

In a dielectric material the Maxwll's equation becomes: $$ \nabla\times\vec{H}=\vec{J}_f+\frac{\partial\vec{D}}{\partial t} $$ where $\vec{D}=\epsilon_0\vec{E}+\vec{P}$ and so $\frac{\partial\vec{D}}{\partial t}=\epsilon_0\frac{\partial\vec{E}}{\partial t}+\frac{\partial\vec{P}}{\partial t}$. The additional term $\frac{\partial\vec{P}}{\partial t}$ keeps track of any moving charge due to the polarization of the material.

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