# Questions tagged [poynting-vector]

The directional energy flux of an electromagnetic field. In conjunction with Poynting's theorem and the continuity equation, it used to express the conservation of electromagnetic energy, and to calculate the power flow in electric and magnetic fields.

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### Why is the Poynting flux not conserved across the interface between two conducting materials?

This question is part of my attempt to use an answer to another question I've posted on this site. If I have two materials with complex indices of refraction, $\widetilde{n}_0$ and $\widetilde{n}_1$, ...
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### J. J. Thomson's "on momentum in the electric field": can it be true physically?

J. J. Thomson imagined a physical system consisting of one electric field source (charge $q$ or else) and one magnetic field source (magnetic monopole $g$ or maybe magnet or something else), with $q$ ...
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### What does the magnitude of the Poynting vector mean in practice?

I have recently found out that word "intensity" is somewhat ambiguous for electromagnetic waves. I always thought of it as the magnitude of the Poynting vector (field), but this is not ...
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### Momentum conservation in classical electrodynamics

The partial of tensor is equal $$\partial_{\mu}T^{\mu j} = \frac{\partial}{\partial t}T^{0j} + \nabla_{j} T^{ij} = -(\rho \vec{E} + \vec{j}\; \times \vec{B})^{j}$$ where does it come from? In the ...
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### Poynting vector

So I saw this video from the science asylum youtube channel and that guy said "momentum doesn't require velocity" and "if u have a constant perpendicular electric field and magnetic ...
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### Poynting Vector from a Black Body

Suppose I have a cavity with rough walls that is close to an ideal Black Body. For simplicity, assume that it is a square box. I cut a small hole in the box of size $dA.$ Energy would radiate away ...
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### Poynting vector and negative index of refraction

Why are the Poynting vector and the wavevector not pointing in the same direction in negative-index media?
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### Is it true that the Poynting theorem $P=E\times H$ is quite valid for DC circuits?

Can we assume that Poynting's vector theorem $P=E\times H$ is one of the universal laws of physics that applies to electromagnetic fields in AC and DC circuits.Is there A rigorous analysis of ...
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### Fault/Technicalities with poynting theorem

When finding the force on a system of point particles $Q_{1}, Q_{2}$, we need to use the formula $$\vec{F} = Q_{1} \vec{E_{2}}$$ Where $\vec{E}_{2}$ is the field ONLY due to the charge $Q_{2}$, since ...
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### Veritasium Electricity videos: where does the majority of energy really flow? [duplicate]

After watching Veritasium second video on electricity (references at the end), I have some doubts about where the majority of the energy flow actually happens. The reference experiment is the simple ...
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Radiation pressures mathematical expression according to Wikipedia is, $\frac{1}{\mu_0 c}\vec{E} × \vec{B}$ "Radiation pressure is the mechanical pressure(force/area) exerted upon any surface due ...
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### Poynting's theorem ambiguity

So in wikipedia for the Poynting's theorem we have: $-\frac{\partial u}{\partial t}= \nabla \cdot\vec S + \vec j \cdot\vec E$ where: $-\frac{\partial u}{\partial t}$ is the rate of change of energy ...
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### General definition of a standing wave

Question "What is standing wave?" has already been asked. Intuitively we all know what it is, but how would we define such a wave in the most general way: for arbitrary geometry, dispersion, ...
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### Poynting vector and $E = hf$
Energy flux for an Em wave is defined by the poynting vector $(1/\mu_0) E \times B$ The energy is also proportional to $E^2$ If you take for example the simplest form of generating light, the ...