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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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Predicting the frequency of visible light

Why can't the Standard Model predict the frequency of visible light? For example, were it possible to invent a universally extensive 'field' in which wave properties are inherent, including those of ...
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0answers
24 views

Question about Faraday Cage [duplicate]

I am aware that faraday cage is used to protect electronics from damage. However, if I put a signal generator in a faraday cage and turn the signal generator on, can the frequency still be picked up/...
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64 views

Can light radiation pressure change its own path

Well i have seen that light creates radiation pressure Can two light waves coming from two different direction change each others path?
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2answers
55 views

Will any charge oscillating in space create an EM wave?

Would it be correct to say that any charge oscillating in space (regardless of the spacial amplitude) at a given frequency will emit an EM wave of the same frequency? related: What change in an EM ...
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14 views

Relationship between poynting vector and radiation pressure

I know that When an electromagnetic wave is absorbed or reflected by a surface, the momentum of the wave is transferred to the surface. I also know that for absorption the radiation pressure is 〈S〉/c ...
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2answers
83 views

Can a photon circle a black hole indefinitely?

Does a photon lose energy or redshift as it circles? Will it's wavelength be the rest wavelength with centripetal and gravitational forces exactly cancelling?
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2answers
99 views

Could photons decay into Dark Matter? [on hold]

So, we can "see" 13.7 billion (intentionally not including expansion) light years in all directions and we "see" a red shift. What if, the reason we can't observe photons beyond this limit is that ...
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1answer
50 views

Gamma Photons vs. Muons; Which is more expensive [on hold]

Which one takes more energy to produce? I ask as I theorize that keeping the plasma in a fusion reactor is very expensive. Muons, while useful, are too short lived. Maybe... Keeping the plasma at ...
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3answers
59 views

Can a wave's Poynting vector be in the opposite direction compared to its direction of propagation?

Can a wave's Poynting vector be in the opposite direction compared to its direction of propagation, and if so, what physical implications does it have? As I understand, the poynting vector s can be ...
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Are 5G Radiation dangers real? How is 5G different from other radiation? [on hold]

Government articles such as https://ecfsapi.fcc.gov/file/1053072081009/5G%20Radiation%20Dangers%20-%2011%20Reasons%20To%20Be%20Concerned%20_%20ElectricSense.pdf and sensationalistic media keep the ...
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19 views

Wavelenghs less than Planck Length [duplicate]

Okay all you heavy physics people, be nice. I'm a retired layperson doing some reading. My question is this : at present technology, can we detect (even if we can't measure precisely) wavelengths ...
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Transverse modes in optical resonators

Im struggling with understanding transverse modes in an optical resonator or laser. Hopefully you can solve this mystery for me. Thank you very much! As far as I know, there are two types of modes: (...
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1answer
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Is frequency of Electromagnetic wave it's intrinsic property?

I was solving a simple refraction problem where the wavelength and velocity of the sodium light needed to be calculated after refracting through glass from air. Now after calculation I found the ...
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2answers
44 views

Why do mirrors not follow brewster's angle?

Normally a material will have an angle where the reflected light is completely polarized. Now say we have a mirror (implemented by a conductive silver coating) that reflects most of it's incident ...
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26 views

How to capture the electromagnetic waves on camera? [on hold]

can we capture the waves on camera by any means, has it ever done. Is there anything available even theoretical. How to generate the noise in camera.
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1answer
56 views

What is the present day photon density, $\rho_{\gamma, 0}$?

I'm attempting to perform the integration that will yield the sound horizon at recombination: $$ c_s^2 = \frac{c^2}{3}\left[\frac{3}{4}\frac{\rho_{b,0}(1+z)^3}{\rho_{\gamma,0}(1+z)^4} + 1\right]^{-1}...
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What is the most measurable electromagnetic wave coming from a small, dark, and not necessarily hot object in sky? [on hold]

Optical fibers are recently used to generate some spectroscopic surveys of the universe map based on some projects such as DESI, MOONS, SDSS-V, etc. The current fibers are often sensitive to visible ...
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42 views

Creating light with combining $E$ and $H$ fields

We know that light is an electromagnetic wave. So if we take electric field $E$ and magnetic field $H$, combine them perpendicular to each other, and make them oscillate harmoniously, would it create ...
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0answers
10 views

Addition of 2 planar waves and maximum of real part [on hold]

I'm studying for my optics exam and I'm sitting on this problem which I know is rather basic, but it feels a bit awkward to me. The problem is (roughly translated): for which $\Delta\phi$ is the real ...
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1answer
193 views

To what extent is the heat in the focal point due to visible light?

When focusing sunlight on a piece of paper, e.g. with magnifying glass, the paper will be charred and might eventually even burn (assuming low cloudiness). To what extent is the heat a result of the ...
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2answers
47 views

Why do hot objects tend to emit shorter wavelength? [closed]

So how do the temperature and wavelength related and why do hot objects tend to emit shorter wavelength?
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3answers
81 views

What change in an EM field is required to create an EM wave?

From here To generate a long wavelength requires an aerial of roughly one wavelength in size. and here One of the difficulties posed when broadcasting in the ELF frequency range is antenna ...
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2answers
33 views

Energy change during electron transitions

I was studying Bohr's atomic model and came to know that when electrons make transitions in between the orbits they lose or gain energy in the form of electromagnetic radiations. I understand why they ...
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13answers
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If visible light has more energy than microwaves, why isn't visible light dangerous?

Light waves are a type of electromagnetic wave and they fall between 400-700 nm long. Microwaves are less energetic but seem to be more dangerous than visible light. Is visible light dangerous at all ...
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4answers
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are there changing magnetic and electric fields that are not EM radiation?

Let us consider these two Maxwell equations: $$\frac{\partial \vec{B}}{\partial t}=-\vec{\nabla}\times \vec{E}$$ and $$\frac{\partial \vec{E}}{\partial t}=\frac{1}{\epsilon_0}\left(-\vec{J}+\frac{1}{...
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1answer
20 views

High frequency limit of permitivity function

I am taking a course in solid state physics, and I have a question about the behavior of the (relative) permitivity function $\epsilon_r (\omega) $ for dielectric materials. In the Drude model, we ...
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0answers
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Feynman’s Treatment of an Opaque Wall

First time poster. I’ve been reading Feynman’s Lectures on Physics, and I’ve just finished reading his treatment on diffraction. Feynman described a method of thinking about an opaque wall that was ...
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1answer
27 views

What is a Hollow Core Fiber?

What is the difference between Hollow core Fiber and a normal optical fiber? How does light propagate in a hollow core fiber, what is the mechanism? I want to write a program to simulate the ...
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1answer
27 views

1 Picocuries per liter is how many millirems per year? [duplicate]

How can you calculate how many millirems of radioactive particles occur per year? The measurements don't seem to match up with radon testing information. 333 millirems in a year not accounting for ...
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5answers
2k views

Is the direction of the electric field relative to the magnetic field in an electromagnetic wave a convention?

In an electromagnetic wave. Could the magnetic field be mirrored around the xy-plane? Is there a specific reason that the 2 fields are oriented this way? Is it just a convention?
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2answers
86 views

Are there experimental observations of the Abraham-Lorentz force?

The Abraham-Lorentz force is the force a classical charged particle particle exerts on itself due to its own electromagnetic field. It has a rather simple formula that reads $$ \vec{F}_\mathrm{AL} = \...
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0answers
39 views

Do red lasers shoot longer than green ones?

I am aware of the fact that our eyes are most sensible to green color and therefore green lasers seem stronger than other colors when being scattered through the air. However, since red wavelength are ...
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2answers
65 views

Photons, light and electricity

Light is ultimately composed of photons. Photons are also force carriers of the electrical force. When an electric motor is turning it is photons which are turning it. What is the relation between ...
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2answers
40 views

How doesn't signal amplification by means of antenna defy the laws of thermal dynamics?

According to this video you can amplify a signal by using the water in your head (although you could do the same thing with an antenna.) Does holding the key close to your head somehow drain the ...
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2answers
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Slowly-varying envelope approximation: what does it imply?

I understand that the slowly-varying envelope approximation means that we can write an electromagnetic wave as $$ E(x,t)=V(x,t)e^{i(k_0x-\omega_0 t)},$$ where $$ \left \vert \frac{dV}{dx} \right \...
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0answers
37 views

Fourier transforming properties of a converging lens

Following Goodman's Introduction to fourier Optics argument I understand that a converging lens will introduce the following difference in optical path (see pag.158, 4th edition) $$r^2/2f$$ where $r$...
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0answers
35 views

Trying to make some sense of the cosmological constant

The question is simple: Does the naive reasoning below have some physical sense, or is it pure gibberish junk? (I use $c = 1$ and metric signature $\eta = (1, -1, -1, -1)$) I suppose that the ...
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2answers
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What is meant by a longitudinal electromagnetic wave?

I reckon this is most likely a rather obtuse question, but I was wondering what would be meant by a longitudinal electromagnetic wave? Questions such as this one refer to there being 'no longitudinal ...
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1answer
28 views

How does electron “orbit” nucleon unless 3 coloured charges act like positive charge?

Do quark(s) emit(s) electromagnetic wave otherwise how do(es) electron(s) form an orbital? Can colour charges somehow mimic electric charge? Btw I know quarks interact via strong nuclear force.
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1answer
32 views

Wave Superposition on a crystal

Does the principle of superposition apply for electromagnetic waves on a crystal? So I know that the principle applies for any wave but I don't understand why some books say that doesn't apply for ...
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3answers
108 views

Why light have angular momentum?

Light carries momentum which is an intrinsic property or ability to move something at least how I interpret it, I got no issue on how it is able to conserve momentum when it is absorbed by another ...
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7answers
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Why are longwave radio towers so tall?

They are often in the hundred meters high. See the wiki link: https://en.wikipedia.org/wiki/Longwave Why are they so tall? Because the wavelength is long, so the antenna should also be long? But to ...
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4answers
81 views

When photons are moving at the speed of light, how come they change in position?

From what i know, photons are moving at the speed of light and that means the time that photons are experiencing is zero, but here is the thing... If the time is zero how can they travel astronomical ...
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1answer
45 views

The relationship between material properties and EM wave frequency

Assuming an EM wave traveling inside an electrically neutral dielectric material. The following electric field describes the EM. $\vec{E}(t,x)=20\cos(\omega t-50x)\vec{u_y}$. Using the 3rd Maxwell ...
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How to describe black body radiation using quantum mechanics

Consider an ideal blackbody. Let us assume that there are enough electronic levels in the body so it can absorb radiation at all wavelengths. (This was discussed in an earlier question) While most ...
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1answer
49 views

Electromagnetic Waves - Amplitude

If light travels as a wave rather than a straight line there should be a width limit for it to travel and penetrate matter - like a hight limit for automobils in roads due to bridges - My question ...
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4answers
106 views

Exceeding the speed of light [closed]

I understand that the speed of light c is derived from the self-interaction between elections/photons, and is thus the maximum speed of anything composed of electrons/photons. Suppose that there is a ...
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0answers
45 views

Power radiated by a vertically oriented bar magnet rotating around a vertical axis?

One very interesting problem: How to calculate a bar magnet (in vertical direction) rotating around a vertical axis, to radiate the electromagnetic waves? For instance, please see the figure below: ...
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3answers
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Can very very few photons form the EMWs?

One maybe interesting question please! In quantum point of view, the electromagnetic waves (EMWs) consist of photons. However, if there are only very very few photons, can they form a wave-like macro ...
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3answers
45 views

How can we relate the wavelength of light to the length of a transmission line?

For the wavelength in free air we have $\lambda = \frac{c}{f}\, [\rm{m}]$, but how does it relate to the length of a transmission line? My question is because of the following example from this site: ...