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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Confusion about energy transport in a circuit
I have some confusions about how to imagine energy flow in a circuit. Imagine for example just a simple circuit with a battery, two wires and a light bulb.
According to classical Electrodynamics the ...
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Geometrical and wave physical effects
Is it right to say diffraction is a geometrical optics phenomena and scattering a wave physical effect? I am considering a finite-length conducting plane and supposing a wave hitting the surface and ...
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How can we prove for magnification of an astronomical telescope?
It is known that when we increase the length of the tube of an astronomical telescope the magnifying power decreases, how do we prove it?
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How does Planck's Constant solve the ultraviolet catastrophe?
I am studying black body radiation and a high school level for a class. My understanding of it is this:
There is a finite frequency light and therefore amount of ultraviolet light objects can emit. ...
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What is the smallest possible wavelength? [duplicate]
I was thinking about this the other day after a quantum mechanics lecture (unrelated to the lecture I was taking) and pondered "Is there a minimum wavelength for a photon?", through ...
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The radiation power of an electromagnetic wave scatter due to the magnetic field
In studying the scattering of an electromagnetic wave by a single charge, it seems typically we consider the motion driven only by the electric field, as is presented in Section 32-5 Scattering of ...
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Can the time varying Intensity of an electric field of a wave be measured?
Lets say that we have a detector which we use to measure the intensity. Theoretically, the intensity is a varying function of time (When we calculate the Poynting vector) but often in textbooks they ...
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Michelson interferometer: beam splitter affects amplituedes?
Let's suppose an initial plane wave $\vec{E}=\vec{E_0}e^{i(\vec{k}\cdot\vec{r}-\omega t)}$ enters a Michelson interferometer . Let $\vec{E_1}=\vec{E_{01}}e^{i(kz-\omega t)}$ and $\vec{E_2}=\vec{E_{02}}...
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Japan's Maglev Train propulsion and guidance system [closed]
Above image is taken from Japan's Maglev Train youtube video by Lesics at here.
If the electromagnets along the two walls used for guidance of the train (So that it does not hit the walls) is made up ...
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Light, Work, and the 2nd Law
I am trying to figure out what restrictions there are on converting light energy into work.
I understand that solar energy can be converted to electrical energy with roughly 90% Carnot efficiency. ...
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What happens in a conductor when the electric field has a plasma frequency?
The complex index of refraction for a conductor is given by the equation: $$N(\omega)=n+ik=\sqrt{1- \frac{\omega_p^2}{\omega^2+i\gamma\omega}} $$ where $\omega_p^2=Nq_e/\epsilon_0m_e$ is the plasma ...
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Relativistic Effects on Electromagnetic Wave Propagation
So for a recent lab I had to calculate the length of a conductor by measuring the time it took a signal to reflect off of the open end. I used the very simple principle of $v=st$ and, knowing that the ...
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Thomson Scattering when low intensity light meets an orbital electron
Can you explain to me the reason why Thomson Scattering can not explain what happens when light meets an electron at low intensity, and what does that have to do with light being a wave or particle or ...
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Why does an charge free space always create an oscillating field?
My question is on the nature of oscillating electric field. From Maxwells equation, we know that the solution of the electric and magnetic field for an empty space are always oscillating fields. I ...
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Spontaneous emission as dissipation and fluctuation
Suppose we have some sort of medium and we want to build an effective theory of light inside. Of course we want to calculation the dielectric constant, which in turn is determined by the ...
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When exactly does a change in $E$ or $B$ result in an electromagnetic wave?
I am always wondering why only accelerated charges emit electromagnetic waves, while constantly moving ones do not.
I imagine an electron in else empty space moving with speed $v$. The $E$-Field in a ...
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Question regarding synthetic UV sources (fluorescent, LED) and claims to "match the sun"
I am involved with some discussion regarding lamps specifically in use for reptiles. Captive reptiles can often suffer from hyperparathyroidism from a lack of vitamin D. The safest way found to ...
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How do i calculate change of momentum when I send a photon in the direction of travel
Say a spaceship is traveling at a certain velocity v (>>c) and it emits light from the nose of my spaceship in the direction of travel. The speed of light is finite and hence there should be a ...
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Poisson spot amplitude
The equation
$$
U(P) \propto \int_0^{2\pi} \int_0^{\infty} g(\rho,\theta) \exp\left[ \frac{i\pi}{\lambda}\left(\frac{1}{z_0} + \frac{1}{z_1}\right) \rho^2 \right] \rho \, d\rho \, d\theta
$$
or the ...
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Tangential component of the "electric" vector spherical harmonic $N_{lm} = \nabla \times (h X_{lm})$?
So I want to solve the problem of an electromagnetic plane wave scattering by a sphere myself, and one of the crucial steps is to solve the scattering of a converging TE- or TM-polarized vector ...
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Interpretation of watts per square meter for intensity of radiation
The energy that an electromagnetic field can deliver to a system is proportional to the square of the field. However, we use the terminology watts per meter square to represent the amount of energy ...
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How exactly are incident EM waves cancelled by a conductor, and why only on one side of it?
This answer describes why EM waves from inside a microwave are blocked by the metal mesh screen:
The incident EM wave induces oscillations in the metal of the screen, and these oscillations reradiate ...
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From the physics standpoint, how should I align a USB Internet stick relative to the nearest cell tower in order to have the best signal? [closed]
I use this USB Internet stick:
(Huawei E3372h-153)
To connect to the Internet, I simply insert a SIM card into this stick and then insert the stick into a USB port of my laptop.
Based on my ...
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Photon emission rate frequency dependency
I am puzzling over the dependence of the energy flux of electromagnetic radiation on the frequency of the source.
The power radiated in any direction or solid angle from a charged particle ...
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Why is aurora borealis circular in shape when viewed from space?
These are some false color images of the northern lights captured by NASA's satellite Dynamics Explorer-1.
Image credits: Dynamics Explorer - 1 (DE-1)
Spin-Scan Auroral Imaging (SAI)
Photo Gallery
It'...
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Why do parabolic antennas need to be the same width as their wavelength?
I am reading the wikipedia page for parabolic antennas, and have a question about the below quote:
In order to achieve narrow beamwidths, the parabolic reflector must be much larger than the ...
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How do you visualize an electro-magnetic wave?
How do you visualize an electro-magnetic wave? If there is a very narrow beam (like the one produced by may be a maser?) confined within a few centimeters (in its wave-front) with amplitude say x, ...
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Incompatibility of the Lorentz force with electromagnetic radiation
Let's consider a charged particle with a fixed speed along the x axis (for convenience). There is no external electric field $E$. If this particle enters a region of space with a constant magnetic $B$ ...
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Can something become hot enough that it stops glowing?
So I understand that matter emits EM waves when hot. And that the higher the temperature, the shorter the wavelength, so cooler flames start off orange and the hotter flames reach light blue and white....
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(A10) If light is an EM wave, can it interfere with electrons in a live wire, leading to a change in the wire's current?
Here's my question: If light is an electro-magnetic wave, with oscillating magnetic and electric fields, wouldn't light interfere with the free electrons flowing (slowly) in a wire, as the electric ...
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Second Harmonic Generation in metals
Assuming a metal driven by a femtosecond laser pulse could generate second harmonics, are these harmonics radiative?
In other words, do they reach the far-field?
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Can an Electric and Magnetic fields be non-perpendicular? [duplicate]
Can an Electric field and a Magnetic field be non-perpendicular to each other$?$ If yes, can an electromagnetic wave pass through that region$?$
I think that yes, both can be non perpendicular to ...
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Terminology: angular frequency vs frequency
I am confused about the usage of the terms frequency and angular frequency in physics texts. E.g. in the book "Classical Electrodynamics" of J.D. Jackson, one considers in formula (7.3) page ...
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Why isn't the penetrating depth of electromagnetic radiation consistent with its frequency?
If I trust a quick Google search:
Microwaves at 2.45 GHz can penetrate 17 mm through muscle tissue (source).
Visible light only 1-5 mm and ultraviolet something like 0.2 mm (source).
But now X-rays ...
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Relativistic correction of Coulomb's Law
I am attempting to describe Coulomb's law but with the delay one would get because of the light speed limit. I am aware one could do that using Maxwell's equations because they are relativistic, but ...
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What is Helicity in High Harmonic Generation?
The harmonic spectra are calculated as $|FT(\frac{d}{dt}\mathcal{J}(t))|^2$, where $FT$ si the Fourier Transform and $\mathcal{J}(t)$ is the current. We need to identify which multiple of incident ...
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Prism: full spectrum including UV + IR
When shining a white light source through a prism, one will see the spectrum of it—so a lot of colors depending on the type of light source.
However, I would also like to see the invisible part of the ...
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How does a photon interact with EM field of a nucleus thus exchange momentum and recoil the nucleus when pair production happens? [duplicate]
The photon must be near a nucleus in order to satisfy conservation of momentum, as an electron–positron pair produced in free space cannot satisfy conservation of both energy and momentum.[4] Because ...
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Passing electricity through magnets [duplicate]
Looking to link up with someone who has experience with electricity and magnets. I’m wondering if you can pass electricity through magnets similar to a wire.
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Why does a blackbody object emit light if it only absorbs light?
I have learned that a blackbody object only absorbs light and thus does not reflect any light. The blackbody object will, however, emit light, and none of this light is due to reflection. Where does ...
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What is the entropy increase associated with the absorption and remission of solar radiation? [duplicate]
The average solar irradiance over the Earth is 1361 W/m2 with a wavelength distribution given by Planck's law for a temperature of about 5778 K. Approximately, the same amount of radiation is re-...
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Fermat's principle of least time confusion
The link is: https://www.feynmanlectures.caltech.edu/I_26.html#Ch26-F3
Hi, I'm reading Feynman's lecture on Optics: The principle of least time, and I'm wondering if I got what he's saying right. For ...
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Can we say that amplitude of light scattered by air molecules is inversely proportional to the square of wavelength of incident light?
As per Rayleigh's criteria of scattering of light by air molecules the intensity of scattered light is inversely proportional to the forth power of wavelength.
AND WE ALSO SAY :
Intensity of a wave ...
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How to understand the Orbital angular momentum of a photon that is not an integer？
How to understand the topological charge that is not an integer, how would the signal OAM crosstalk if one were to model its transport in turbulence, for example, if the beam carries a topological ...
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What is the interplay between radiation and photon creation?
While trying to provide an answer to this question, a question popped into my mind. When a charge accelerates, is there always a photon associated with that radiation, or multiple photons? For ...
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Why take into account deceleration radiation only, but not acceleration radiation when Bremsstrahlung happens?
Why only take into account deceleration radiation rather than the radiation caused by acceleration when going tangent towards the nucleus and acceleration caused by the change in direction when flyby ...
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Does a running motor generate photons?
Since a motor consists of electric field generated through AC current and a fixed magnetic field (permanent magnets), does it generate photons?
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How does an antenna emit photons at a specific frequency if the antenna is made up a specific metal (Al) for example?
My base assumptions...
An antenna emits energy over long distances in the form of photons.
A photon is emitted when an electron changes energy state from higher to lower levels.
A photon's "...
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How can "kinks" in electrical field and changing electrical and magnetic fields can work together to produce EM waves? [duplicate]
I am trying to understand how electromagnetic waves are created and I've 2 explanations:
Vibrating electrically charged particle creates a changing electrical field, which creates magnetic field, ...
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If light is made up of electromagnetic waves, then if I put a magnetic close to a laser beam, shouldn't the light bend? [duplicate]
Light always moves in a straight line unless gravity acts on it strongly, but since it is made of electric and magnetic waves, shouldn't it be pulled towards different charges and magnetic, or is ...
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