Tob Ernack
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Can $E=\frac{q}{4\pi\epsilon_0 r^2}$ be directly derived from differential form of Maxwell equations?
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6 votes

When you have a point charge, the charge density is not really defined, as it is basically infinite at the origin, and zero everywhere else. You would need a distribution rather than a function to ...

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Why does critical damping return to equilibrium faster than overdamping?
2 votes

What the OP asks for is indeed possible but only for very specific initial conditions. There are a few things to discuss, the first being what does "returning to equilibrium faster" mean. ...

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Is there a difference between metal waveguides in microwave frequencies and dielectric waveguides in optical frequencies?
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2 votes

There is reflection at the boundary in both cases, but the reason is fundamentally different. The reflection at the boundary of a perfect conductor arises from the boundary conditions $$\mathbf{E} = \...

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Calculating average of normal Poynting vector for evanescent wave
1 votes

I realized soon after writing the question that the quantity is indeed real. That is because for evanescent waves, the normal component of $\mathbf{k}$ is purely imaginary but the transverse component ...

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Force on a Magnetized Body in a Non-Uniform Magnetic Field
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1 votes

Assuming the magnetic field is linear (i.e. we can Taylor expand $\mathbf{B}$ around the origin and truncate all terms of order higher than $1$), then you are correct. The formula is also ...

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Changing Refractive Index
1 votes

The refractive index of a dielectric material with nonlinear behavior can also be changed by an application of an external DC electric field. This is called the electro-optic effect (or Kerr effect) ...

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Why do bound charges not appear in boundary conditions on a surface between two dielectrics?
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1 votes

You can imagine that the dielectric is composed of a large number of molecules and ions. The molecules/ions consist of a group of charged particles interacting together sufficiently strongly that they ...

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Is there a better definition of magnetic field than this?
1 votes

The magnetic field is an instance of what is known mathematically as a "vector field". This is a function from a vector space to another. For example, most physical vector fields would be functions ...

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Transmitted Power and Poynting's theorem contradiction?
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0 votes

I came back to this problem a few years later, and I finally figured out what was wrong. First of all, the Poynting vectors are indeed conserved across the boundary (placed at $z = 0$), but you ...

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