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# Questions tagged [electromagnetic-radiation]

Propagating solutions to Maxwell’s equations in classical electromagnetism and real photons in quantum electrodynamics. A superset of thermal-radiation.

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### What can I put in my microwave oven that won't get warm?

I have a fuzzy understanding that microwaves heat food because the waves interact with polar molecules in the food, causing them to vibrate, and the vibrations are heat? Correct me if I'm wrong. To ...
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### Diffraction limit PSF and angular spectrum method?

I know from the angular spectrum method that given a field $U$ with a wavelength $\lambda$, we can decompose it with Fourier transform. U(x, y,0) = \int \int {\tilde{U}_0(f_x,f_y)} ...
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1 answer
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### Which is the real cause of the radiation reaction force exerted on a charge?

In David J. Griffiths' Introduction to Electrodynamics, Third Edition, he says that radiation reaction is the recoil force exerted by the radiation emitted by an accelerating charge. In the next ...
0 votes
1 answer
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### Why is the value of volume charge density $ρ$ zero in lossy medium?

Given is the page of a book which I was studying. I was trying to study the derivation of the wave equation in a lossy medium. As I have underlined a sentence that says, "most of the case in ...
1 vote
2 answers
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### What mode of atom excitation is responsible for light slowing in transparent media?

Refraction index (or speed of light in a transparent medium) is often explaned as light interacting with atoms in a way such that the atoms create a secondary wave that once added up to the primary ...
-5 votes
1 answer
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### Do gravitational waves cause matter to radiate?

Gravitational waves distort the "fabric" of spacetime. In doing so, it seems they can cause particles to accelerate. On the other hand, textbook electromagnetism predicts accelerated charges ...
0 votes
1 answer
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### Why is the refractive index of blue light larger than red light in water while the refractive index of radiowaves is larger than both?

So I thought the reason why radio waves have a relatively high refractive index in water is because they have a low frequency which increases the permittivity, but blue light that has a higher ...
1 vote
1 answer
300 views

### Circular antenna array

At page 20 of http://read.pudn.com/downloads773/doc/comm/3065154/5237234.pdf the two formulas that characterize the behavior of a linear and a circular antenna array are compared. The reason why I ...
2 votes
1 answer
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### Intensity of Compton scattering photons

In various sources (1, 2, 3, 4, to name a few) I have seen this graph shown below, that shows how intensity depends on the wavelength of the scattered photon $\lambda'$. Now, I do understand what ...
1 vote
0 answers
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### What is the relative polarization between the two photons created during matter-antimatter annihilation?

During matter-antimatter annihilation two photons are created. What is their relative polarization? Are they both linearly polarized in the same orientation? Linearly polarized perpendicular to one ...
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### Is the Planck Relation linear at high energies?

As the title suggests, I'm wondering if any deviation from $E = h\nu$ has been observed when the wavelength of light approaches the Compton wavelength of the electron, proton, etc.
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### Zero-dispersion wavelength

Please help me understanding the zero-dispersion wavelength in fibers. I found this wiki-article on the topic. Accordingly: "In a single-mode optical fiber, the zero-dispersion wavelength is the ...
-1 votes
1 answer
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### Stefan-Boltzmann's law independence of surface density

One thing about Stefan-Boltzmann's law didn't make sense to me is that the radiated power density is independent of the particle density of a surface. It seems like things have to cancel out amazingly ...
1 vote
1 answer
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### What happens to light that never hits anything?

Im a blue collar worker, just had a thought. What would happen to photons that never hit anything. It must be possible that at least one photon out there somewhere just happened to not ever hit ...
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2 answers
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### How can any object except Plasma emit white light or be a blackbody--it seems contradictory?

How can any physical object absorb and emit white light when all objects are made from atoms and molecules, each of which has its own absorption/emissions spectrum that acts as it's signature “...
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### Is there a substance which can pass both IR and UV radiations?

I have been thinking about this for a while. A quartz prism allows UV Radiation to pass. A rock salt prism allows IR radiation to pass. Glass absorbs both. Is there something, that is, a substance to ...
2 votes
2 answers
345 views

### Momentum of light in anisotropic media

This question is related to the Abraham-Minkowski controversy that has already been discussed extensively here and in the research community. But I want to ask about an aspect of this momentum ...
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### How to use dipoles to enforce the boundary conditions for a spherical dielectric with complex permittivity

I want to impose an electric and magnetic field on a spherical dielectric of radius $R$ and relative permittivity $\epsilon_r=\epsilon'+i\epsilon''$. Say the fields are slowly-varying (like a plane ...
0 votes
2 answers
126 views

### Diffraction when the wavefront is not parallel to the plane

I am studying Feynman's chapter on the origin of the index of the refractive index (see this link). If I am not mistaken, what he does is to prove that when a wave enters a medium (modelled as a ...
2 votes
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### Link between photon helicity and polarization of $A^\mu$ electromagnetic potential

From Wigner theorem we know that the irreducible unitary representation of the Poincarè group for massless and spin 1 particle is labelled by the momentum $p_\mu$ and the two possible helicity $+1,-1$ ...
1 vote
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### Low frequency video transmission

Can a video signal be transmitted for a short distance ($30\,\mathrm{cm}$) by a very low frequency carrier ? Here my concern is about frequencies $1\,\mathrm{hz} - 100 \,\mathrm{hz}$ . Transmission ...
1 vote
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### Does electric and magnetic field from electromagnetic radiation are 2D based? [closed]

I'm getting into physics, specially in electromagnetism. When we're talking about electromagnetic radiation. Does it has a 2D shape when it's propagating through space? Does Maxwell's equations ...
2 votes
1 answer
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### Can Stern-Gerlach spin alignment be seen as a result of EM radiation of precessing magnetic dipole?

Stern-Gerlach experiment is often seen as idealization of measurement. Using strong magnetic field, it makes magnetic dipoles (of e.g. atoms) align in parallel or anti-parallel way. Additionally, ...
8 votes
4 answers
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### How can photons interact with nuclei?

How can photons such as X-rays or gamma rays interact with the nuclei of atoms given that, as I understand it, the length scale of a nucleus is around a couple of femtometers? So, shouldn’t the size ...
-4 votes
2 answers
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### Can we catch signals from a cellphone using an external device? [closed]

What if someone stole em waves from our mobile devices to listen to our conversations or get our OTP. Whatever encryptions they have they are just EM waves innit and they cannot be propagated only in ...
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### How well does a cavity with a hole approximate a black body?

Cavity with a hole is a frequently cited approximation to a black body (more precisely, it is the hole that is the black body here): Is there a simple estimate of how well such a cavity approximates ...
7 votes
7 answers
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### How does light beyond the visible spectrum relate to color theory?

Like if you put a red spotlight and a blue spotlight on the same area, the light ends up magenta. And if your light is purple and you have a yellow chair, the chair will appear black because the ...