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 light only emitted by atoms? i.e are they the only source of light in the universe?
This is a very trivial question I suppose.
But, I dont remember any other sources of light mentioned anywhere other than the atoms emitting radiation due to electrons changing energy levels.
So, are ...
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Can bremsstrahlung, cyclotron radiation, or Larmor radiation flip the spin of a particle?
There are many situations where a photon is emitted from a charged particle because it accelerates. This includes bremsstrahlung, which is usually a charged particle scattering of a nucleus and losing ...
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Hi, I have a little doubt, do electric charge create EM field or disturb or enhance it? [closed]
What i mean to ask is that, i learnt that EM waves are just disturbance in the already ever existing EM field, so when there is a charge in space, does it enhance the field in its required direction ...
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Light Spectrum - Sum of Waves or Collection of Waves
I am wondering about the spectrum of light that is often shown pictorially as a distribution of power, say, from sunlight. My question is: does this indicate that each wave of light contains all of ...
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Why do accelerating electrons emit radiation?
I know how you can emit light with an alternating current, running back and forth, creating an electric field in addition to the magnetic field.
But why does an electron emit light when it gets ...
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Is Wikipedia wrong about Huygens-Fresnel Principle?
Someone posted a question about why backward waves don't exist according to the Huygens-Fresnel principle: Why doesn't a backward wave exist?
In following up on this question I read the ...
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Antenna as a heat exchanger in the magnetocaloric effect
Consider a refrigerator based on the magnetocaloric effect.
During the adiabatic demagnetization stage that starts at $T_h$ and bias field $H=H_{max}$ going to $H \to 0$ the magnetic dipoles relax and ...
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Does fog produce right-handed or left-handed circularly polarized light?
I have read that when unpolarized light travels through the water droplets in fog, it becomes circularly polarized, but is this polarization right-handed, left-handed, or both? And what would ...
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Rabi Oscillations: $\pi$-Pulse vs a single photon
I am puzzled by the following:
Assume an atom as a two-level-system.
A $\pi$-Pulse acting on an atom in the ground state promotes this atom in the excited state. This is done by a continuous ...
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Why do microwaves penetrate flesh when visible light does not at the same intensity?
I understand why microwaves penetrate flesh, it has been answered before here, but in the most answers it was mentioned that although microwaves have less energy per photon when compared to visible ...
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Why does light not propagate backward in dense media?
It is easy to see how light propagating in a dense medium destructively interferes laterally and constructively interferes in the forward direction. This is why light will travel forward in such a ...
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Why does the intensity get low when the frequency gets high according to the Planck Diagram? [closed]
In my text book it states that the intensity should be very high for high frequencies however in the diagram it shows very low intensities. I know it has something to do with the quantum effects but I ...
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Does a rotating ring of charge radiate power or not?
The Larmor Formula suggests that the power radiated by an accelerating charge is non zero. But we know that a uniformly charged non-conducting ring rotating about its central axis does not radiate. ...
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Ways Light Can Interact With Matter
Below you will see how my "understandings" and obsevations are in conflict. Please look them over and let me know what I am missing.
Absorption: Light can only be absorbed by an atom if it ...
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How and why do accelerating charges radiate electromagnetic radiation?
Let's consider it case by case:
Case 1: Charged particle is at rest. It has an electric field around it. No problem. That is its property.
Case 2: Charged particle started moving (it's accelerating)....
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De Broglie wavelength of a photon
The de Broglie wavelength of a photon and the wavelength of its corresponding electromagnetic wave are numerically the same. Is this just a coincidence and the two waves are different or is the de ...
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Permittivity of plasma in electromagnetic wave
Suppose an electromagnetic wave with frequency $\omega$ propagates through plasma with free electron concentration $n$. The formula for the permittivity in terms of the frequency
$$
\epsilon = 1 - \...
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Deriving solution for wave equation using retarded Green's function
In the book Advanced Classical Electromagnetism by Robert Wald, it was shown if $\psi$ satisfy the homogeneous wave equation
$$\square\psi=0$$
then we have
$$\psi\left(x^{\mu}\right)=-\frac{1}{c} \...
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Why is energy not conserved instantaneously in electromagnetic waves? [duplicate]
I don't know if its a valid question but it's been bugging me for a while so I'll ask it.
I know that the Poynting Vector $\vec{S}$ gives the intensity of the electromagnetic wave, and its related to ...
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$\rm Lux$ to $\rm W/m^2$ conversion?
For a physics project, I'm planning to investigate the relationship between the number of slits in a diffraction grating and the intensity of the central maxima. The light meter which I'm planning to ...
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Experiment Prediction: How much light can pass through an opening?
The flow of current through a wire is limited to the size of the wire. Water through a pipe is limited by the size of the pipe. What about light? Is it limited in a similar way?
Let's say I drill a 1,...
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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 ...
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Does Special Relativity apply to waves or particles?
I know that Special Relativity is a classical theory, so perhaps it applies to light waves, but I'm not too sure. The question I want to ask is, does Special Relativity set a bound on particle ...
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Why does my UV LED flashlight feel warm on my skin while my IR flashlight does not? [duplicate]
Both are 18 watts. Shouldn't IR feel warmer on my skin?
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Frequency of the photon in general relativity
There is an observer at ($r,\theta, \phi$) outside of the Schwarzschild blackhole. A beacon is falling into the black hole along $r$ coordinates of the metric and is emitting radiation. At $r_{em}$, ...
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What is the difference between antenna input impedance and its radiation resistance?
I got to know that the input impedance of the halfwave dipole antenna is given as:
$Z_{in}$=1/$I_m$* sin($\beta$(H-|Z|))
where $I_m$ is the maximum current on the antenna( when excited with a 1 volt ...
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Is there a difference in the 'quality' of a gas if it's heated by electromagnetic radiation as opposed to conduction/convection?
According to this link, "The wavelength at which the $O_2$ molecule most strongly absorbs light is approximately $145$ nm."
According to this link, that's in the ultraviolet range of the ...
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Different color between sunset and daytime
When we look at the sky, it's blue because blue light has shorter wavelength, so it scatters more energy; and at sunset we see a red sky because most of the blue color is scattered out. What I don’t ...
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Pressure due to a single photon
I'm interested in the pressure exerted on a material when a single photon is absorbed.
I have written the following expression for pressure:
$$
P = \frac{hf}{cA\Delta t},
$$
where $A$ is the area over ...
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Can electromagnetic waves be polarized without any being absorbed or blocked? (I.e., no energy is lost?)
I guess what I am asking is this:
When a light source is suddenly polarized in a certain direction, is it because all of the constituent waves not already polarized that way are blocked, reflected or ...
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Why can't de Broglie waves be electromagnetic in nature?
We know that the wavelength of de Broglie waves for a photon is same as that of the wavelength of the electromagnetic radiation that carries this photon. Doesn't this prove that matter waves are em ...
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What are the odds for detecting radio transmissions from an other civilisation .. Drakes equation with twist
Supposing there is someone out there trying to contact us, what are the odds that we could receive the signal?
What I'm driving at is that Drake's equation tries to estimate the likelihood of ...
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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, ...
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Electric field associated with moving charge
I have recently started to learn about the electric field generated by a moving charge. I know that the electric field has two components; a velocity term and an acceeleration term. The following ...
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Why can't a reflective barrier raise an object's temperature past a heat source's temperature?
Say I have a 1 $m^2$ source of visible light emitting 1,000W worth of light. This is shining down upon 1 $m^2$ of ground.
If we treat the ground as a blackbody, my understanding is that eventually it'...
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Can transverse waves be both mechanical and non-mechanical?
Transverse waves need a medium for particles to propagate perpendicular to the wave right? Then how can transverse waves be non mechanical which do not require any medium?
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Why can't fire heat something hotter than itself, but electromagnetic waves can heat something indefinitely?
Part of my question on Can a low-energy source/object heat a higher-energy object via radiative heat transfer? asked if a 100W lightbulb could heat a blackbody in a vacuum indefinitely, presuming ...
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Cavity and black body radiation
If one speaks of the fact that one gets blackbody radiation in good approximation by a cavity with hole, does one mean as blackbody this hole, i.e. the place where the radiation exits from the cavity? ...
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Which parts of the electromagnetic spectrum cannot be used for remote sensing of the Earth system and why? Is that different on the moon? Why?
Which parts of the electromagnetic spectrum cannot be used for remote sensing of the Earth system and why? Is that different on the moon and if yes, why?
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Light from a nuclear explosion in space
If someone detonates a one megaton nuclear bomb in space, how far will it be visible to the naked eye? Of course, I am aware that there is no medium in space that can glow, so all the light would come ...
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Would a radio frequency (RF) laser have any advantage over ordinary radios?
In the radio part of the electromagnetic spectrum it is really easy to make very clean and powerful RF waves using modern electronics, and it really isn't that hard to make arbitrary RF waves.
But ...
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Is $∫ (1/2)εE^2 dV$ in the entire volume of rays propagation $= nhf$?
I asked it on ChatGPT but it gave kind of a mixed answer contradicting itself in the process several times here is some of it.
"Kushagra Singh:
~so you mean $∫ (1/2)εE^2 dV$ in the entire volume ...
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Why does UV light feel warm on my skin? Whereas infrared light heats up space around me plus my skin?
Noticed something weird today.
I have an infrared space heater that is pretty good at heating up my desk at work (as well as my skin obviously).
I also have a UV flashlight. I noticed the UV ...
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Is a photon a single wavelength of monochromatic light?
I am confused about all these different interpretations of what a photon is?
I am looking for a simple and practical interpretation.
Therefore, I am asking herein if a single photon corresponds to a ...
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If a pulse is reflected by a mirror that absorbs part of its spectrum, must it become longer?
There is a pulse of duration $T$ supported by a certain bandwidth $\omega$.
The pulse is reflected by a mirror that absorbs part of the spectrum.
Does the pulse become longer?
Is there a situation ...
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About kinematics of electrons in a circuit
We know that electrons flow in a circuit due to the electric field, so shouldn't the electrons be accelerating, but we also know that
$i=neAv$ so from here we can conclude $v=i/neA$ which is a ...
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Energy-work theorem and dissipation of energy by an accelerating charge
By the work energy theorem we have that the total energy of a nonrelativistic point charge, $q_0$ of mass $m$, moving in an electric field $\mathbf{E}$ is
$ E = E_k + U_e = \frac{1}{2}mv^2 + q_0V \...
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Why don't we get infinite energy from a continous emission spectrum?
If the spectrum emitted contains all kinds of photons of all kinds of wavelengths, doesn't that mean it should have infinite number of photons of very small energies? For example, 4000 angstrom to ...
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How to decipher imaging method used in remote sensing images?
I am working on remote sensing for science olympiad (div c) and i am kind of lost on remote sensing image analysis. like how do i look at an image and know it was captured using infrared or microwave ...
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Is there any example where electric and magnetic fields are not perpendicular?
Perpendicular electric and magnetic field creates light or other electromagnetic waves. Is it a necessary property to have a perpendicular fields? If not what would happen when the fields are not ...
