Propagating solutions to Maxwell’s equations in classical electromagnetism and real photons in quantum electrodynamics. A superset of thermal-radiation.
2
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2answers
158 views
A charged sphere with pulsing radius
Radius increases and decreases periodically (as a pulse).And so does the charges on the surface of sphere.
I can't get what is gonna happen.the EM waves are produced perpendicularly to motion of ...
4
votes
2answers
179 views
How photons represent colors that you see?
Right now, my understanding is that, a mixture of photons of many different frequencies is perceived as white by your eye. While no photons at all, is perceived as black. And photons with the blue ...
11
votes
6answers
602 views
What are the various physical mechanisms for energy transfer to the photon during blackbody emission?
By conservation of energy, the solid is left in a lower energy state following emission of a photon. Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium ...
1
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1answer
84 views
The length of an antenna is twice the amplitude of the wave
I have seen it remarked in some problem sets that if you have an electromagnetic wave traveling in the $x$-direction with it's $y$-coordinate given as
$y(x,t)=y_0\sin (\omega t +kx)$
and you want a ...
1
vote
0answers
23 views
Does shadow fading change if obstacles are fixed?
Given a RF sender and a receiver, suppose the obstacles between them are fixed, both their material and dielectric properties, does the path loss caused by their shadowing vary? If yes, what causes ...
2
votes
1answer
96 views
Mirror problem of radiation pressure
If two perfect mirrors are placed facing one another and they are in proximity, and photons (don't ask me how) are traveling between them and toward one of them, what is to keep the radiation pressure ...
0
votes
1answer
55 views
Possible to generate an electromagnetic field from moving an object through a magnetic field?
Is it possible to generate an electromagnetic field from a stationary rare earth magnet with a hole in it by passing an object through the hole?
By definition, a Lorentz Force is the force on a ...
1
vote
1answer
62 views
Can I perceive the photoelectric effect as “ionizing with EM force”
The photoelectric effect demonstrates that EM radiation has particle-wave duality and it can be used to generate electricity. I am still a novice in physics and my understanding of this phenomenon is ...
1
vote
3answers
39 views
Trapping EM radiation
Is there a material which can allow light (or any other EM radiation) to pass through from one side as if it is transparent but its other side reflects light like a mirror?
3
votes
1answer
76 views
Monochromatic wave
If we have an EM wave like this one:
$$E=\begin{pmatrix}1\\i\\0\end{pmatrix}e^{-i(\omega t-kz)}$$
The wave has clearly only one frequency $\omega$, but is it monochromatic? My doubt is that it's ...
1
vote
1answer
158 views
Two photons transition
if an atom in its ground state is coupled to an electromagnetic field it can absorb a photon if the EM field contains one with the right frequency. These transitions depends on $⟨f|H_i|i⟩$ (from ...
0
votes
0answers
41 views
EigenMode expansion for beam propagation
I want to understand how to apply EigenMode expansion method (http://www.photond.com/files/docs/PW03_eme_paper.pdf) for beam propagation on a system of lenses.
The interface between two mediums of ...
9
votes
4answers
571 views
Why does the speed of light $c$ have the value it does?
Why does light have the speed it does? why is it not considerably faster or slower than it is? I can't imagine science, being what it is, not pursuing a rational scientific explanation for the speed ...
4
votes
3answers
151 views
Does light really “travel”?
From what I've so far understood about light, a photon is emitted somewhere and after some time it's absorbed somewhere else.
Have we had experiments that confirm the path taken or something akin to ...
0
votes
0answers
44 views
Should a 1D Guassian wave oscillate?
I wrote a few lines that numerically solve Maxwell's equations.
The result is a moving wave that looks like a single pulse.
This looks strange to me because I expect waves to move in oscillator ...
0
votes
1answer
35 views
Produciton of EM waves with differing wavelengths
Sun is the major source of electromagnetic radiation. Then if the source is the same, how are different EM waves with differing wavelengths produced?
0
votes
1answer
45 views
Red/Blue Shift in EM Waves
A Doppler weather radar operates at a frequency of 3.40 GHz. The wave
from this radar system reflects from an approaching weather system
moving with a speed of 39.0 m/s. What is the difference ...
1
vote
2answers
204 views
Does the intensity of dipole radiation fall as $1/r^2$ or $1/r^3$?
I have seen this derivation:
I want to estimate what is the intensity of the electrical field as
function of $r$ the distance from the radiated source ?
I think it is can modled as pointed source ...
7
votes
2answers
219 views
Can light waves cause beats?
My question is pretty brief. When two sound waves of nearly same frequencies interfere, we get beats.
But, I have not observed something like that happening in the case of light. In fact, most of the ...
1
vote
1answer
49 views
What was the first ionization radiation?
While trying to make somewhat of a timeline of the history of ionizatig radiation, i am wondering about the following questions:
The first photoelectrical effect was found 1839 by Alexandre ...
0
votes
0answers
71 views
Absorbance by using Poynting vector
How should I compute the amount of energy of an EM wave absorbed in the material?
Can I just use the divergence times the Poynting vector?
1
vote
2answers
101 views
Do photons actually generate a slight kinetic force?
My question is even though photons have no (rest) mass, do they emit a external force due to EM radiation causing electrons to be excited and jump to higher energy shells which electrons have mass ...
2
votes
1answer
74 views
Holograms? Sci Fi or future fact?
Based on how light behaves when it passes through mediums, i.e. the wavelength of light changes when it passes through mediums of different refractive indexes, wouldn't it be possible to convert ...
2
votes
0answers
140 views
Classical blackbody radiation 'solution'
I never understood how the equipartition theorem was applied electromagnetic waves inside the metallic blackbody. As hyperphysics puts it ...
4
votes
0answers
47 views
How strong must a signal be at the edge of the Solar System to penetrate into the Sytem?
A sort-of follow-up to Are the Voyager probes still sending us a signal ?
Still following on the news report referenced in the above question, this report indicates further magnetic surprises at, or ...
0
votes
1answer
101 views
The nature of light
I'm not sure if this has been answered before, but I figured this would be the right forum to find out. I'm not by any means an expert in physics, just someone who's interested in understanding more ...
1
vote
2answers
90 views
Radiated power from a 'source volume' outside which charge & current are zero (i.e. derive radiated power from Jefimenko's equations)
In classical electrodynamics, what is the radiated power from a generalized source (consisting of charge density $\rho$ and current density $\vec{J}$) in vacuum?
Let us define $V_s$ to be the ...
3
votes
1answer
83 views
Why does electromagnetic waves travel slower in well isolated conductor?
Wikipedia writes, that
Propagation speed is affected by insulation, so that in an unshielded copper conductor ranges 95 to 97% that of the speed of light, while in a typical coaxial cable it is ...
5
votes
2answers
190 views
If photons move linearly, what's actually stopping them from passing through a microwave oven mesh?
So, my understanding is that the wavelength of a photon is the distance traveled in the time it takes it's magnetic field to oscillate. And it's inversely proportional to it's energy and it's ...
1
vote
1answer
84 views
Eikonal approximation for wave optics. Why follow the unit vector parallel to the Pointing vector?
The description of the passage from wave optics to geometrical optics claims that light rays are the integral curves of a certain vector field (the Pointing vector direction, normalized to 1). Here ...
0
votes
2answers
214 views
EM waves: How do they travel for billions of km without damping
If a star is 1 billion light years away, it means that the light we see from the star is emmitted billions of years ago.
How does this light not undergo a frequency change or get damped inspite of ...
1
vote
2answers
182 views
What is light, and how can it travel in a vacuum forever in all directions at once without a medium?
I know there are many questions that are similar (maybe identical?). I am not a physicist nor a student - I am just interested in physics and have been watching many physics channels on youtube ...
0
votes
2answers
231 views
Young's Double Slit experiment question
Q-A beam of light consisting of two wavelenghts 600 nm and 450 nm is used to obtain interference in Young's Double Slit experiment (YDSE). Find the least distance from the central maximum where the ...
3
votes
1answer
148 views
Computer-Generated Holograms: I'm completely lost. How are they physically implemented?
I have been reading about holography, and I think I understand the general concept, but one thing that has me completely lost is how computer generated holography works in practice.
I think I get the ...
1
vote
2answers
98 views
Can the speed of an electromagnetic wave be measured in the absence of neutrinos?
Let me explain better: from what I understand neutrinos are so pervasive they are literally everywhere. And since they have such a tiny electric charge they barely interact with anything and cannot be ...
2
votes
2answers
100 views
How much better is salt water at letting through microwaves than pure water?
Radio Wave Attenuation
There are two general types of matter (substances) in the universe
that affect electromagnetic waves, conductors and insulators which
are called dielectrics by ...
4
votes
4answers
314 views
Can a photon get emitted without a receiver?
It is generally agreed upon that electromagnetic waves from an emitter does not have to connect to a receiver, but how can we be sure this is a fact? The problem is that we can never observe non ...
0
votes
1answer
24 views
Measuring life through radiation
Dramatic title, I know. But it's shorter than Measuring a person's effective mass through radiation and comparing it to their weighed mass and I figured this would get people's attention.
I just ...
1
vote
2answers
90 views
Do Nuclear Power Plants have shutdown and cooling systems protected from a nuclear generated EMP?
Forty years ago, I read a report concerning the difficulties of protecting my companies equipment, which was to be installed in Air Force One, from a Nuclear EMP. An EMP generated by a high altitude ...
0
votes
1answer
84 views
Circular Polarization
As one observes an clockwise (cw) circular polarized electromagnetic wave which is reflected off a denser medium or metal interface it is changed to a counter-clockwise (CCW) polarized em wave plus a ...
0
votes
1answer
99 views
Photons, no energy? [duplicate]
I am only 14, so I don't know much about physics, and I would appreciate help on this topic.
A photon, is said to have 0 mass. However, they carry energy, as electromagnetic radiation. Albert ...
7
votes
2answers
147 views
What exactly is the difference between a sychrotron light source and a free electron laser?
Cyclotron radiation is radiation emitted by a charged particle being bent by a magnetic field. The only difference between cyclotron and synchrotron radiation is that the latter occurs at relativistic ...
0
votes
2answers
73 views
Why wouldn't Hubble's Law be directly in units of frequency?
Maybe using this as an example:
The energy of a particular color of yellow light is $3.44 \times 10^{-22}$ $kJ$
So if I want to find frequency of that light, I take that number, divide by $h$ ...
1
vote
0answers
21 views
Phase functions non-existent in original (J. Strutt) Lord Rayleigh's work?
This is related to my previous Phys.SE question on the derivation of the phase function - upon sifting and scanning through 600 pages of John Strutt's collected work, there is absolutely no mention of ...
3
votes
1answer
181 views
How did Lord Rayleigh derive/determine the phase function for his scattering model?
I've been researching the question for quite some time, as I understand it the phase function is actually an approximation due to the particle-wave duality inherent in participating media such as the ...
0
votes
0answers
213 views
What is the correct definition of “group velocity dispersion”?
When we talk about a medium with dispersion, we can define the phase velocity $v_\phi = \omega/k$ and the group velocity $v_g = d\omega/dk$. Likewise the phase index $n = c/v_\phi$ and the group index ...
2
votes
2answers
285 views
Harvesting electricity in the air from power lines:
Recently I came across this quote on the internet, about a person who apparently set up devices to extract electricity from the "air", on his own property:
I read an article a couple of years ago ...
7
votes
5answers
478 views
Why Does Light Not Become Polarized In A Magnetic and/or Electric Field?
I am familiar with the Faraday Effect, but I remain confused as to why the electric and/or magnetic components of light do not naturally align themselves with a magnetic or electric field (in a ...
1
vote
1answer
127 views
How photons move along with EM wave?
So the wave moves like. a wave, it moves up and down, up and down. But how do photons move? Do they follow the same path or do they just go straight forward without oscillating?
0
votes
0answers
53 views
Currents and fields of a magnetron
I can't make heads or tails of the descriptions of magnetrons (i.e. microwave) I'm reading online. Hyperphysics does the best job of illustrating fields and currents, but the story of its operation ...
