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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Is there a definition for wavelength of a non-plane wave?
For example, a wave with wavefronts that are not equally spaced from each other, is there a definition of wavelength?
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how is polarization distributed in a point source spherical EM wave?
if we take an very small point source of EM wave, we will find that the EM wave is polarized. How does the polarization vary depending on which point of the sphere ?
Polarization is always shown along ...
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Is temporal wavelength of a wave always equivalent to its spatial wavelength? [closed]
I can't see how it would be possible for these two to be different.
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Do high speed particles see light as a different part of the EM spectrum due to the Doppler effect?
If a particle was travelling fast enough and had visible light shot at it, would the partice experience the light as if it was higher or lower wavelength? If so, would the particle see the incident ...
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How is temporal frequency multiplied by spatial wavelength equivalent to velocity?
My book seems to be implying that the temporal frequency when multiplied by the spatial wavelength gives the velocity of the wave. I cannot see how this is true. Can someone explain?
Here are ...
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Using complex exponential to represent waves in EM [duplicate]
Ever since we've been using exponentials to work with electromagnetic waves, I've been confused about the imaginary portion and want to confirm my thinking.
What does the imaginary portion represent? ...
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How can light travel in a vacuum? [duplicate]
Lets get on to it!
we know that a wave is simply a disturbance in a certain surface or any kind of a field and this should be common to every wave even light.
The problem comes with the property of ...
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finding the direction of magnetic field given the electric field and k vector
My notes have stated that the relations between direction of electric and magnetic field is as follows:
$$ \frac \omega k \vec B_0 = \hat{\vec k} \times \vec E_0$$
where $\hat{\vec k}$ is the unit ...
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Can something not reflect visible light?
Is it possible for something to not reflect any visible light (for humans)? Eg can something only reflect infrareds or ultraviolets or gamma rays etc.?
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Why cathode rays produce visible light on hitting glass but X-rays on hitting denser material?
Why cathode rays produce visible light on hitting glass but they produce x rays on hitting denser material ? I mean what is the difference in denser atoms that cause x rays rather than visible light .
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Is light a discrete or continuous phenomena?
Image a light bulb. In it the filament with a simple metallic composition, copper or other metals. At the precise instant, say $t=0$, where the first copper atom will be shining.
In which direction ...
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Red shifted to what?
I searched and found a lot of questions and answers about red shift here but none with the answer to mine. (sorry if it is there somewhere and I did not find it.)
Everyone is saying the light from ...
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Whats behind light? [closed]
Once the light is emitted as a pulse, and once that pulse has passed, what's behind it? Is light a continuous wave, or only a wavefront? What is left in the wake?
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Are oscillating magnetic field sources always accompanied by an electric field?
E.g. consider a rotating magnetic dipole. Does the rotating dipole also generate a propagating electric field "disturbance"?
Basically, is the stereotypical in-phase, orthogonal electric/magnetic ...
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Can an electromagnetically induced dipole be explained with photon interactions?
An incident electromagnetic wave will cause a dipole moment in the medium it passes through, displacing positive and negative charges in accordance with the EM field. How much of this interaction (if ...
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The interstellar medium reflects extremely low-frequency radio waves. Could we use this fact to build a more efficient photon rocket?
According to the equations of MHD, electromagnetic waves cannot propagate in a plasma if they are below the plasma frequency. (For more information, see this question about astronomical-wavelength ...
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What was Planck's motivation for the frequency dependence in $E=nh\nu$?
Many accounts of the history of quantum physics explain how Planck resorted to quantizing energy in an "act of desperation" while attempting to solve blackbody radiation, only to discover by surprise ...
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Do bigger stars emit higher amplitude waves?
So I’ve been reading about luminosity and I get the concept of the size and temperature determining the intrinsic brightness and total energy emission of the star. I also understand how the further ...
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Radiation Pattern for a Dipole Antenna with non-sinusodial forcing voltage
I was wondering, how does one derive the radiation pattern for a dipole antenna if you don't assume a sinusoidal forcing function? It seems this assumption kind of ignores the most important question ...
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Highly conductive lossless medium
I've came across the term "highly conductive lossless medium" in the context of electromagnetic waves travelling in materials.
I'm wondering how to make sense of that statement? I thought "highly ...
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Is it possible to see traveling light beams?
As we all know the speed of light is the thing that allows us to see
Now let's imagine a beam of gamma rays from a Black hole just a few light years away passing through the solar system somehow was ...
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Varying magnetic field creates varying electric field. Does constant magnetic field creates a constant electric field?
Varying magnetic field creates varying electric field. Does constant magnetic field creates a constant electric field? If yes, an simple wire(like on picture, for example) with DC power will attractes\...
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Does EMR emanate in all directions? Does the wave expand like a sphere surface whose radius grows at $c$?
I made a commitment to understand special relativity.
Right now I'd like to understand Electro-Magnetic Radiation. What would it "look like"if I could see it emanate. From a book (Simply Einstein) ...
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How likely is it that photons will interact with electrons?
Electrons are incredibly small, and the "size" of photons (or the distance away from one required to not interact with it) is also incredibly small. Yet photons still interact with electrons all the ...
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How is energy conserved in spontaneous emission?
I was reading through the section on spontaneous emission in Introduction to Quantum Mechanics (2nd Ed.) by Griffiths. In section 9.2.2 he explained that spontaneous emission is really a stimulated ...
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Is it possible to break a carbon dioxide molecule using electromagnetic waves?
I'm no expert in physics, but I was just wondering if breaking apart $\rm CO_2$ into oxygen and carbon would be possible using certain electromagnetic wave?
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Energy and Poynting vector in a solenoid
We have the following scenario.
A long (ideal) solenoid, with $n$ turns per unit lenght, is carrying a current $I$. At the beginning, the current is constant and we have a magnetic field
$$\mathbf{B}...
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Explanation of consistency between Maxwell's equations and the existence of photons
I have limited knowledge of QM but I know some about electromagnetism. I have read some about the photon description and I am confused.
How can EM waves be viewed as a continuous, changing field but ...
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Huygens Principle, what's the benefit to this interpretation?
I don't understand what's the point in interpreting a wavefront as point sources emitting spherical waves. You then need to use magnetic and electric currents to explain away how there are not ...
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What happens to the diffraction pattern of light as an aperture becomes infinitely small?
Will the point source according to Huygens principle start radiating backwards with nothing to cancel it out?
Will it be a complete sphere if light passes through an infinitely small aperture?
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Plane wave propagation constants being equal across all components
Starting from the wave equation for electric field in free-space,
$$ \nabla^{2}\boldsymbol{E}+k^{2}_{0}\boldsymbol{E}=0, $$
where $k_{0}$ is the free-space wavenumber, we usually proceed in deriving ...
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Smallest Packets of Electromagnetic Wave - Confused
I heard that the smallest units of electromagnetic wave packets is a single photon. Why can't we have the electromagnetic wave intensity to be smaller? Since we're changing electromagnetic waves can't ...
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reflection coefficient derivation for normal incidence emr
Starting with the boundary conditions for parallel E and B fields for emr normal to an interface, i am trying to derive reflection coefficient with refractive indices.
I have got as far as
$E_1=...
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Can refractive index be used interchangeably with wave impedance?
Everything I've been taught so far for EMR and waves at an incidence has been using the refractive index.
for example, the reflection coefficient for a wave normal to an incident is
$$R = ((n1-n2)/(...
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Why are electromagnetic waves inverted when reflected at a fast to slow medium boundary?
I've been taught before that mechanical waves, when they hit a boundary between a less dense (faster) medium and a more dense (slower) medium, the reflected wave is inverted because it acts like a ...
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How is comparing $|E|^2$ to $|H|^2$ relevant?
I am reading one article that compares two kinds of electromagnetic surface waves, but the following figure confuses me:
Why instead of comparing $|E|^2$ and $|E|^2$ do they compare $|E|^2$ and $|...
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How does a Tesla coil make fluorescent light glow?
I know that the secondary coil used in the Tesla coil radiates electromagnetic waves in the surroundings.
This radiation makes the electrons in the fluorescent material of the light oscillate, and ...
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Why does dispersion of light behave in the opposite way for diffraction compared to refraction?
When blue light is shined through a diffraction grating it bends less than a longer wavelength, let's say red light. The shorter the wavelength the less it is bent by diffraction. When the same ...
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Unpolarized EM wave: is there no electric/magnetic field? [duplicate]
I'm not understanding what an unpolarized wave is. Does that mean there is no electric/magnetic field, or that the field is constant, i.e. frequency = 0? How can that be possible?
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Internet - mobile phone vs wifi
wifi cost me like 30USD while mobile internet 10USD, I thought to save this monthly bill by purchasing a mobile-phone-router. The only thing that blocks me from that is radiation. I'm far fetched ...
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Can my theory work for letting the swinging work?
This is my theory, will it stop after few hours? why would it stop? i have on top S to S to repel then i have N S to attract, to produce random force for the swing. Then i have large N N repel to push ...
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Why has it taken so long for people to talk about using Far-UVC light for disinfecting?
If you don't know what I am referring to you can see this simple TED talk https://www.youtube.com/watch?v=YATYsgi3e5A. There are also many articles online about it.
After watching that TED talk, all ...
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Bending light due to gravity
My question is can you consider the fabric of spacetime to be a medium? And if so, can one explain the bending light due to gravity, that warps spacetime, as analogous to light changing between the ...
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A summation in quantum optics paper
I am going through the paper "Moments of $P$ functions and nonclassical depths of quantum states", which contains the following passage:
A. Thermal state
The density matrix of the thermal ...
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Why are the $\mathbf E$ and $\mathbf B$ fields of an electromagnetic wave mutually perpendicular?
Why are the wave number $\mathbf k$ and the electric and magnetic fields $\mathbf E$ and $\mathbf B$ are perpendicular to each other?
I know it but I haven't thought about it deeply.
How can I prove ...
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Calculation of Poynting vector of standing electromagnetic wave
I have this question in my homework where I have the following phasor of the electric field (we assume that all waves have $\omega$ frequency):
$$\overline{\mathbf{E}}_{1}\left(x,y,z\right)=E_{0}\left[...
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Is it possible to divert light and/or wave by light or wave?
Is there a way to divert (deviate, deflect) light (photons) by another light (such as laser) or ...
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Why polarization filter do not dim the light completely?
In a circle there's infinite amount of degrees (eg. 0 deg, 0.00000000000...1 deg etc.) In a ground school we are thought that there's 360 degrees in a circle.
A landscape behind my window is ...
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Corrections to plasmons theory. (History of Plasmons)
Is it true that around 70's there was a huge change in theory that describes plasmons (SPP, to be precise)? Recently I stumbled upon an interesting (but old) paper about plasmons. Authors of that ...
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Thermal Radiation of human body
I've read that all bodies emit electromagnetic radiation of all wavelengths. Does this mean that humans emit gamma rays too (excluding the radiation from radionuclides present in humans)?
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