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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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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 ...
Newtron Malayalam's user avatar
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0 answers
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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 ...
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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 ...
Plop's user avatar
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Dipole antennas and the $B$ field

A dipole antenna responds to the electric component of a EM wave. Does the magnetic component of a EM wave have any effect on the performance of a receiving dipole antenna?
Rich D's user avatar
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Will an electron release energy when it is added into an atom for which electron affinity value is negative (endothermic)?

According to my understanding, when an electron is added into an atom, it emits energy in the form of photons because it is a form of de-excitation or relaxation. This is when electron affinity will ...
SameerTahir's user avatar
6 votes
7 answers
3k views

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 ...
Madeira Darling's user avatar
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1 answer
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Why is the length of a Faraday cage's lattice relevant to what wavelengths it blocks?

I believe the title is self-explanatory. I see a similar reasoning pop up often in other areas where EM radiation is being manipulated, e.g. lasers, radars, radio telescopes and so on. The wavelength ...
Paghillect's user avatar
1 vote
0 answers
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What actually happens when light goes into a waveguide?

I have only dealt with a rudimentary theoretical treatment of how light propagates inside a waveguide, such as those available in Griffiths. One thing bugging me is that I still do not know how ...
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About the notation for TEM waves

I just came across this article where the term "$\mathrm{TE}_{101}$ microwave mode" is mentioned. Other than the basics of TEM waves which I learned in Griffiths, this is the first time I ...
hendlim's user avatar
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15 votes
7 answers
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Why does the length of an antenna matter when electromagnetic waves propagate perpendicular to the antenna?

The optimum length for a dipole antenna is a multiple of half the wavelength that it is designed to receive or emit. Why is this? If an electromagnetic wave has E in the x-axis, B in the y-axis, and ...
user411769's user avatar
2 votes
0 answers
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Direction of propagation of extraordinary wave inside a birefringent medium

I am reading Optics by Ajoy Ghatak, in which the author explains the phenomenon of double refraction in a calcite crystal using Huygens' principle. My query is in the analysis of the case of normal ...
Enigma's user avatar
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1 answer
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Why does radiation of small wavelength interact with small objects?

I was reading chapter 2 from the book 'Diagnostic Radiology Physics : A handbook for Students and Teachers', and came across the following quote "X rays of energy of a few tens of ...
In the blind's user avatar
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0 answers
26 views

Solarization Spectrum

I'm looking to better understand the relation between the spectrum of the light which induces solarization in glass and the spectrum of the induced absorption. More specifically, I'm interested in ...
Yuval Weissler's user avatar
3 votes
3 answers
181 views

Photonic black holes

"Can a photon turn into a black hole?" - usually the answer to this question is - it can't, because it has zero rest mass. However, when we derive the Schwarzchild Metric initially the $2M$ ...
Nayeem1's user avatar
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1 vote
1 answer
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Is it possible for both electric and magnetic fields to have longitudinal component in a rectangular waveguide?

I know a rectangular waveguide cannot support TEM waves, but supports TE and TM waves. In the TE mode, $E_z=0$ and in the TM mode, $H_z=0$ (where propagation direction is along the $z$-axis). I want ...
Saurabh Bhurewar's user avatar
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0 answers
96 views

How to compute the diffraction efficiency of a thin phase grating with arbitrary groove shape?

From Magnusson and Gaylord (1978), the wave amplitudes, $S_i(z)$, of $p$-polarized light for a thin, arbitrary phase grating are given by the equation $$ \frac{\partial S_i}{\partial z} + \gamma \sum_{...
Roy Smart's user avatar
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1 vote
1 answer
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Confusion regarding phase

As far as I know about phase if the phase difference between two waves is positive, the former is leading..and the latter is lagging. Then why has D J Grifith stated this? If the phase of the magnetic ...
Suhail Sarwar's user avatar
6 votes
2 answers
585 views

Could a transparent frequency-altering material be possible?

I would imagine a material that is transparent but a electromagnetic wave going out will have a lower frequency than when going in (and maintaining it's direction). You could build glasses to see UV-...
Walter's user avatar
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1 vote
1 answer
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Can an optical medium be lossless and dispersive?

Occasionally, I come across the phrase "lossless dispersive linear optical medium". How can such a medium be possible mathematically? I mean the real and imaginary parts of the electric ...
apadana's user avatar
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3 votes
1 answer
101 views

About electron radiation frequency in Heisenberg's 1925 paper

In Heisenberg's 1925 article Quantum Theoretical Interpretation of Kinematic and Mechanical Relations, one of the first things he establishes are the form of the frequency functions in (what I assume ...
11 votes
4 answers
2k views

Can the laser light, in principle, take any wavelength in the EM spectrum?

Can the laser light, in principle, take any wavelength in the EM spectrum? I don't think there is what prevent this in principle, right?
Jack's user avatar
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2 votes
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ELF Electromagnetic wave propagation in plasma (ionosphere) - how?

Can an extremely low-frequency electromagnetic wave (below 500 Hz for example) propagate through an ionosphere? The cutoff frequency of Earth-ionosphere waveguide is approximately 1.7 kHz so I ...
Leif's user avatar
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1 answer
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How many photons pass through us every second?

I just read this answer https://physics.stackexchange.com/a/229374, which says that, when a magnet rotates, photons are emitted with wavelength $λ=c/f$, where $f$ is the frequency of rotation. And ...
Flamethrower's user avatar
0 votes
4 answers
128 views

Why should an electron falling into the nucleus, according to the Maxwell's laws of electrodynamics, destroy the atom?

It is often said in physics and chemistry classes and textbooks that atoms must be unstable when the electron continuously loses energy and finally fall into the nucleus according to classical physics....
Learner's user avatar
5 votes
2 answers
512 views

Does the Larmor Formula assume circular motion?

The Wikipedia page on the Larmor formula says that the Larmor formula makes the unavoidable assumption that the charged particle is orbiting in a circle. This quoted sentence isn't true, correct? I ...
tparker's user avatar
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8 votes
5 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 ...
EigenDragon16's user avatar
1 vote
2 answers
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Is luminescence from impact of fast neutral atoms/molecules on a suitable substance known?

Cathodoluminescence is emission of photons by electrons impacting on a luminescent material. The Rutherford scattering experiments detected impacting helium nuclei on a phosphor screen. Many other ...
Ritesh Singh's user avatar
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2 votes
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Why does oxygen green (S1) emission in aurorae only occur at lower altitudes? [duplicate]

Aurorae have a red color at high altitudes caused by the excitation of atomic oxygen and the subsequent emission at about $630 \,\text{nm}$. This happens at high altitudes because at that height there ...
jack_O'Dim's user avatar
7 votes
1 answer
742 views

Can gravity radiate?

In electromagnetism, when a charge accelerates, it emits radiation. We know this because we can write the retarded potentials, apply $\vec E=- \nabla V-\frac{\partial \vec{A}}{\partial t}$ and $\vec B=...
Lagrangiano's user avatar
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10 votes
3 answers
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What do we mean when we say the CMB has a temperature and how do we measure it?

I have read this: An object without any internal degrees of freedom, like a single photon, can't really have a temperature. But an ensemble of photons can have a temperature. If you put an ensemble ...
Árpád Szendrei's user avatar
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0 answers
27 views

dipole-radiation in semiclassical dynamics solid state

Using the semiclassical dynamics in solid state physics (electrons on a lattice with periodic potential, constrained to a band structure), we usually obtain that in the presence of external fields (...
Noam Ophir's user avatar
0 votes
1 answer
115 views

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 $\widetilde{n}_1$, ...
Roy Smart's user avatar
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0 votes
2 answers
51 views

Confusion about EM spectrum and the Fourier transform

Since courses on signal analysis and electromagnetism I have become confused about what the spectrum of electromagnetic radiation really means. I know light is when electric and magnetic fields become ...
Jelle 3.0's user avatar
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0 votes
1 answer
24 views

Dipole radiation of a non-relativistic electron in elliptic motion [closed]

I'm trying to solve the following problem: A non-relativistic electron is moving in elliptical motion inside a positively charged cylinder of homogenous charge density $\rho$. The initial radius ...
zare023's user avatar
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2 votes
1 answer
47 views

Is there a way to use the optical transfer-matrix method to determine the absorbance of each layer in a multilayer stack?

I've implemented the transfer-matrix method to determine the the transmittance and reflectance of a multilayer stack of thin films. I know that (ignoring scattering) the absorbance of the entire stack ...
Roy Smart's user avatar
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-1 votes
1 answer
55 views

Do bosons exist at different energy densities?

Excuse my rudimentary (at best) physics knowledge, but I was running a thought experiment earlier (read musing to myself). I was wondering whether a photon could be considered analogous to bowshock, ...
cockbeard's user avatar
1 vote
3 answers
113 views

If quaternions are an extension of complex numbers, is there a study of EM wave theory in terms of quaternions?

I find that in standard textbooks and online resources, basic EM wave theory (such as radiation, plane wave solutions, polarization) is discussed by treating fields in terms of complex numbers. Is ...
RajaKrishnappa's user avatar
2 votes
0 answers
62 views

The $\alpha$ particle's energy inside a nucleus is lesser than the Coulomb barrier height. Justify

The $\alpha$-decay is usually explained via quantum tunnelling. This is because the $\alpha$ particles do not have sufficient energy to climb over the Coulomb barrier. But how do we know this? We can ...
Solidification's user avatar
0 votes
0 answers
42 views

Spherical laser beam terminology

I am currently seeking the correct terminology for a beam that expands linearly from a fixed point, resulting in its wavefronts forming spherical surfaces. However, the beam does not expand in all ...
mathslover's user avatar
6 votes
4 answers
2k views

Accelerating Expansion of Universe - Why Not Caused by Radiation?

As I understand it, dark matter and dark energy are used as an 'explanation' for how universe expansion is accelerating; because without it gravity would be expected to cause a long term shrinking. ...
Claud's user avatar
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0 answers
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What is the solar radiative power on a clear sky day through a surface which is parallel to the sun's incidence on Earth?

Assuming that the solar power through the incident surface is known. How can we calculate or estimate the radiation through the parallel surface assuming a clear sky? Looking for watts per square ...
mr chap's user avatar
  • 111
1 vote
2 answers
166 views

How to solve Relativistic Lorentz Force equation if $\gamma$ is not constant?

I am trying to numerically obtain the trajectory of an electron inside a periodic magnetic field $\mathbf{B}$, taking into account that the relativistic factor $\gamma$ is not a constant (the electron ...
Joan Arenillas's user avatar
0 votes
2 answers
42 views

Stars that have fairly high gravitational redshift and calculation of their surface temperature by Planck emition spectra?

How high can the ratio between gravitational redshift and planck emition spectra be depending on the mass of the star so by how much this gravitational redshift could elongate the Planck spectra of ...
Krešimir Bradvica's user avatar
5 votes
3 answers
2k views

Is it possible to get an electromagnetic wave equation if the speed of light were infinite?

In an old question: How would night sky look like if the speed of light was infinite? the best answer was voted down to negative credits. I cannot understand why. From Maxwell's equations, we derive ...
wiljo's user avatar
  • 59
1 vote
1 answer
87 views

What is light? how is it connected to electromagnetic radiation?

I am trying to understand how light works and electromagnetic radiation, from what I understand charges cause disturbances in electric fields, which triggers a magnetic field, and then the back and ...
Ranvir Choudhary's user avatar
0 votes
0 answers
38 views

Cross section along the single transmission path of electron

I am studying this research paper "Forecasting of ionospheric vertical total electron content (TEC) using LSTM networks" about ionosphere, but in introduction section I phrase I didn't ...
D. S.'s user avatar
  • 101
30 votes
5 answers
14k views

How can a point source emit spherical EM waves when they are forbidden by Maxwell's equations?

I know that there exist plane wave solutions to the Maxwell equations in free space, and I tried solving them for a spherical wave emanating from a point but could find no solution consistent with the ...
Thanos's user avatar
  • 419
0 votes
1 answer
42 views

How could I calculate the strength of an electromagnetic field sufficient enough to generate plasma in low pressure argon gas?

For context, I wish to create a plasma toroid in a glass sphere of 25 Torr Argon gas like in the photo below; there are multiple examples of how to do this online using a class E oscillator ...
MXVG's user avatar
  • 1
139 votes
2 answers
71k views

How many photons are received per bit transmitted from Voyager 1?

As of 2024, according to https://voyager.jpl.nasa.gov/ , Voyager 1 is around one light·day away from Earth and still in radio contact. When Voyager 1 sends messages to Earth, roughly how many photons ...
Craig Gidney's user avatar
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7 votes
7 answers
4k views

Is it impossible to construct a Faraday cage that can block a *static* electric field?

I think the answer is yes. My reasoning is this: Imagine for argument's sake, we could have a charged negative source that has its field blocked by a Faraday cage. We can transport a positive charge ...
KDP's user avatar
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