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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Any method to detect extremely weak electromagnetic wave signal? (10^12Hz, level ~10^(-28) Watt per meter^2 per Hz)

Could you please let me know whether there is any method on the Earth to detect some EXTREMELY weak electromagnetic wave signal, if it is a planar wave, if its exact waveform is completely known (...
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State of the electromagnetic field due to spontaneous emission in Wigner-Weisskopf approximation

Background These lecture notes describe spontaneous emission of a two-level atom using Wigner-Weisskopf theory. To summarize, they describe the state of a two-level atom and electromagnetic field as ...
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COMSOL Cherenkov radiation

As indicated in the title of the discussion, I would like to know if it would be possible to simulate through software based on the finite element method COMSOL Multiphysics the movement of a particle ...
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Zeros of Optical fibers characteristic equation at cutoff

The exact procedure to obtain such zeros is often omitted in textbooks, and this article is cited: E. Snitzer, Cylindrical Dielectric Waveguide Modes, Journal of the Optical Society of America, Vol. ...
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Quantic superposed state photons beam intercepted by a polarizing filter

Let's say that we have got one coherent light (same frequency, same phase) beam of photons which are in a quantic superposed polarization state (half H polarized / half V polarized photons). This beam ...
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Rudimentary electromagnetics/shielding questions

I am trying to expand my knowledge in the field of electromagnetics and I have a number of related questions if anyone is able to help. Patience appreciated. For what incoming frequencies does a ...
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Electronic motion due to circular polarization

I came across a question where the situation was of electronic motion of left circular polarized wave in a ionosphere plasma of electron density $3\cdot 10^{11}$ and external magnetic field $B_0$ in $...
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Pair production: photon collides with an electron

During pair production, a high energy photon collides with an electron which then creates an electron–positron pair, but what happens to the electron that the photon collides with? I am asking ...
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How do low frequency radio waves bend due to diffraction? [closed]

I did not understand how do surface waves follow the curvature of the earth by diffraction. Here is an excerpt from the book that I was reading from. ...
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What really determins the color of light? [duplicate]

I have been considering this problem: Colour is characterized by which of following character of light? a)Frequency b)Amplitude c)Wavelength d)Velocity Different websites claim ...
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EM wave reflection on a perfect conductor

Suppose the region $x>0$ of 3D space is a perfect conductor, and the region $x<0$ is vacuum. You send a monochromatic plane wave $\vec{E_i}=\vec{E_0}e^{i(\omega t-kx)}$ from the left to the ...
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Does diffraction limit on light divergence apply to all beams?

The diffraction limit $\theta = {\lambda \over\pi w}$ is generally referenced as a theoretical lower limit on light beam divergence. However this limit seems to be based on the assumption that a ...
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Does phase velocity or group velocity change when light enters a new material? Contradictory sources

I'm so confused. I've read in this book (page 28) that group velocity of light can exceed $c$ in certain gases. However a lot of people online and in the forums say that phase velocity can exceed $c$. ...
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Rigorous derivation of Stefan-Boltzmann radiater power (from energy per unit volume)

I was trying to understand page 4 of https://mcgreevy.physics.ucsd.edu/s12/lecture-notes/chapter07.pdf The goal is the following: we start from the E.M energy per unit volume inside the blackbody: $$...
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Sound waves travel with electromagnetic waves?

Do sound waves travel along/with electromagnetism and static electricity from the sun?
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Source of cylindrical electromagnetic waves

I have a question about waves with cylindrical wavefront. Precisely, I have read that they may be generated by a linear source, while for instance plane and spherical waves are respectively generated ...
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Electric field potential on slope of electromagnetic wave and the homopolar (monopolar) generator? [closed]

For public the message is simple: when magnetic field changes there is an electric potential difference created or there is an electric field potential. If you rephrase it, can you say that on every ...
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Natural vs. man-made electromagnetic spectral energy density

Over the past year or so, I've heard several people (not physicists) express concern over the amount of environmental electromagnetic energy from human sources like radio communication, wifi, and most ...
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Can polarization states of a photon be understood in terms of spatial orthogonality/dimensions?

For example, do the terms 'horizontal', 'vertical', 'diagonal' and 'anti-diagonal' polarization have any relevance to the physical, quantum state of a photon, or are they simply descriptive of how one ...
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Can I shake a charge to illuminate my surroundings?

If I put charge on the tip of a rod and shake it back and forth at the right frequency, can I illuminate my surroundings? According to my understanding of Maxwell equations this would create EM waves ...
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Can an electromagnetic wave be pulsated at the same frequency of the wave itself?

This is a thought experiment that's been bugging me for some time and I haven't been able to find any literature on this topic. I am not a physicist, please bear with me :). Suppose I have a 500nm ...
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How does a telescope make an image larger by shrinking it?

I saw these images of how a telescope works and it seems like it is shrinking the image down to the size of the eye. I don’t understand how that makes the image bigger. My thinking is that shrinking ...
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1answer
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Interplay of energy between photon, electronic energy levels and kinetic energy

I can understand that atoms have quantized energy levels for its electrons, but an atom's translational kinetic energy is continuous. As such, why is the absoprtion spectrum not continuous? That is to ...
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Reason for phase change in the electric field oscillations, not the magnetic field oscillations?

Wikipedia states that when an EM wave undergoes reflection, there is a phase change only in the electric field oscillations, not the magnetic field oscillations. It also suggests that the opposite is ...
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Relation between phase change and mass of bodies during wave inversion

Is there a relation which shows how the phase change depends on the mass of the bodies in mechanical wave inversion? This question also applies to EM-waves and any sort of relation to explain their ...
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1answer
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Interpretation and computation of properties and polarization of an electromagnetic wave (transverse wave) [closed]

I would like to calculate the polarization properties of a plane wave (transverse electromagnetic wave), based on values of an export file from an electromagnetic simulation. The values are recorded ...
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Does shaking an atom produce photons?

I have a vague recollection of a description of the relationship between matter and light. It went something along the lines of this: "Grab hold of a thing and ...
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Does a laser's listed wattage or joules include the frequency? Or just the amplitude?

In other words, if the number of photons in two different lasers is the same, but the second laser has a higher wavelength, does the second one have more 'wattage' or more total joules? (Since higher-...
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Has a reflected wave an arbitrary phase shift?

Let an EM wave propagate in the $\hat{z}$ direction - $$\vec{E_I}(z,t)=E_0e^{i(kz-\omega t)}\hat{x}$$ it hits a conducting surface at $z=0$ so there is a reflected wave - $$\vec{E_R}(z,t)=E_{0R}e^{i(-...
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How is magnetic flux viewed in QED?

I know that QED is formulated in terms of Lagrangian density. So when we solve for a physical system we ultimately ends up finding $\psi$ and $A_{\mu}$. I'm not interested in $\psi$ for now. Since I ...
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Reasons for mechanical wave inversion? [duplicate]

General idea (with strings): When a wave in a string in transmitted through 2 different media, a part of it is inverted and a part transmitted. 'Rules:' If a wave enters a region where the wave ...
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4answers
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Peculiar Question: Can Sound travel through particles of Light?

It is a thought Experiment. Imagine a box that is lined on the inside with 100% perfect mirrors. Shine some light into that box and seal the box. The light will bounce back and forth between the ...
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If both violet light and red light was incident on the center of a semi circular block, and refracted, would they have the same refraction angle?

As the violet and red light have the same speed in air, with the incident angle being less than the critical, with the violet light and the red light coinciding on each other, (like on top of each ...
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Why are the electric and magnetic waves produced by an antenna in phase?

From my understanding, an antenna produces an electric field when charges are separated, and produces a magnetic field when they are flowing. However, when the magnetic field is at a maximum, the ...
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Experiment for jammers

I'm going to grade 11 and I have to write an essay in physics. One requirement is to do an experiment which - in the best case - also includes measurements. I would like to write about jammers, which ...
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Speed of light and wavelength

Does the speed of Electromagnetic wave depend on its wave length? For vacuum I'm aware that it's a constant $c=\frac{1}{\sqrt{\mu_o\epsilon_o}}$. Similarly can we say speed of light in any medium is a ...
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Phase difference between source voltage and inductor voltage

What will be the phase difference between the source voltage and the inductor voltage? Will the two voltages be in phase or will be out of phase. How much out of phase they will be? Note that there ...
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Electrons emitting photons. Real life example?

In highschool we are taught about Bohr's atom model and how electrons emit light/ photons when transitioning from a higher energy orbit to a lower energy orbit. First question Where does this ...
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Compton scattering equations

In my book, when it discusses Compton Scattering it provides the following momentum equations, where $\gamma$ is Lorentz factor, $m$ is the mass, $u$ is the velocity, $h$ is Plank constant, and $\...
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How can I make sense of the way (screen) colors are generated? [duplicate]

OK here is some common knowledge I have from the net: a computer screen has 3 constituent colors of red, green, blue. To make all spectra of stuffs it just combines them. We also know that red is ...
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Why does a pinhole create an image of the Sun?

When I was a kid I happened to encounter a solar eclipse. I was taught that I should not look at the Sun directly when it is undergoing an eclipse, but I was extremely curious to see it. Somebody ...
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Why would the frequency of an EMF wave have any relation to the wavelength?

I take a wireless antenna and I run a current through it 3 times per second. I have now created a 3 Hz ELF frequency. According to Wikipedia this radiation has a wavelength of 100000 km. Needless to ...
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Deriving the wave equation for electromagnetic waves

I'm currently referring to the wave equation derivation given in "Introduction to Electrodynamics" by David J. Griffiths. It follows something like this: The electromagnetic wave equations are given ...
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Heat absorbed by a material surounded by a blackbody

Let's assume I have a square surface of area $A$ inside a cavity modelled as a black body. We can assume the cavity being spherical of radius $R$. The cavity is at temperature $T_{cav}$ and my square ...
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Solving the scattering field equations to get FDTD equations

I was going through a paper FDTD method for the scattered-field equation to calculate the radar cross-section of a three-dimensional target published in the Journal of Computational Electronics(2018)....
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1answer
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How to produce light of a certain wavelength?

Is there a device which takes as input the wavelength or frequency value and produces electromagnetic waves of the given wavelength or frequency using an emitter? It might be that the wavelength range ...
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1answer
38 views

Spacing between primary maxima of $N$-slit diffraction pattern and single-slit envelope

As far as I know, in the double-slit diffraction pattern, the spacing between primary maxima is determined by the equation of double-slit interference pattern, and the intensities of primary maxima ...
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Energy information in gamma spectrometry

In gamma spectrometry, energy is deposited in the crystal and the electron from the valence band gets excited to the conduction band. Both bands have degenerate energy levels. More the energy ...
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Resolution of semiconductor vs scintillator

FWHM is low for HPGe detector compared to NaI(Tl). That's is due to the difference in band gap. More electron density in conduction band of HPGe reduces the uncertainty. Resolution improves. ...
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Does light (photons) transfer momentum really directly between emission and absorption?

I have read this question: Does light travel "quantised"? Or , is it perceived as quantised only when it interacts ,i.e, undergoes measurement? The underlying spacetime interval is zero, ...

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