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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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Why is photon quantized in vacuum? [duplicate]

Apparition of quantized energy levels in quantum physics is usually explained in analogy with sound waves in a box (like in music instruments): the wave has to satisfy the boundary conditions and ...
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2answers
41 views

Why does frequency remain unchanged in light refraction but wavelength doesn't?

Since the frequency of an electromagnetic wave does not change during refraction but the velocity changes, the wavelength must therefore change. But why doesn't the frequency change in the first place?...
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Are 5G signals dangerous? [duplicate]

Ive been seeing a lot lately on the dangers of 5g and exposure to the internet and mobile signals but I dont understand why they are considered harmful when the 5g frequency band will be around 25 Ghz....
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2answers
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How strong are Wi-Fi signals?

My family members dislike the idea of having many devices communicating wirelessly in our house, arguing that the signals have negative effects on our physical health. I would like to tell them the ...
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0answers
43 views

How can I get the wave number and wave vector? [on hold]

$$\overrightarrow{E} = (-10 \hat x + 4 \hat z) e^{-j(2x+5z)}$$ I recently started to study electromagnetics, but I'm having a hard time following up. May I ask how to calculate the wave vector $\...
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2answers
33 views

What is the relation between the frequency of the light produced and the acceleration of the charged particle

We know that accelerating charges produce EM radiation. Can we derive a relation between frequency of the light produced and the accelaration of the charge ?
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2answers
23 views

Radio Waves / Light: Atmospheric Refraction

The following image differentiates between a visual horizon and a radar horizon. Sidenote: I'm not too familiar with primary surveillance radar technology, but this image refers to secondary ...
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1answer
55 views

Confusion about derivation of Abraham-Lorentz force

An accelerating charged particle produces EM radiation, so we conclude that there must be a reaction force acting on the particle, leading to the Abraham-Lorentz force: $$ {\bf F}_{rad}=\frac{q^2}{6\...
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1answer
52 views

Why aren't extremely-low-frequency (ELF) radio waves used for underwater radar?

Since extremely-low-frequency radio waves are used by submarines for some simple, low-transmission-rate communications, why can't those same wavelengths be used for submarine radar? It may not be ...
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About the equivalence of two sets of electric fields and magnetic fields [on hold]

How to show the equivalence of two sets of electric and magnetic fields? Reference J.D. Jackson Classical Electrodynamics, 3rd ed., Problem 6.2(c).
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24 views

About Feynman and Heaviside electric and magnetic field [on hold]

How to calculate the magnetic field from the given expression of the electric field? $$ \vec{E}= \frac{q}{4 \pi \epsilon_0} \left( \left[\frac{\hat{R}}{R^2}\right] _{ret}+ \frac{[R]_{ret}}{c} \frac{\...
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0answers
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What is the difference between an electron wiggler and an undulator?

Both wigglers and undulators use periodic magnetic fields applied to stored relativistic electron beams to produce intense beams of UV or X-rays that can be used in a wide range of condensed matter ...
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6 views

Dielectric constant in terms of fundamental forces [duplicate]

How can one explain the slowing down of electromagnetic waves travelling in a medium using fundamental forces of nature like electromagnetism?
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2answers
38 views

What is the force corresponding to Lamor's formula for EM radiated power?

The rate at which electromagnetic energy is radiated is given by Lamor's formula. What is the corresponding rate at which momentum is radiated and hence force to this?
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2answers
44 views

Two questions about the standing waves in a black body

I am currently reading a derivation of Rayleigh-Jeans law for cavity radiation from Eisberg and Resnick 1 . The authors derive the law by considering a cavity with metallic walls. In the book, the ...
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1answer
60 views

Do clouds reflect radio waves?

Do clouds reflect radio waves? Specifically, those waves used in radars. And, what kind of matter refracts or reflects radio waves?
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1answer
40 views

How do electrons ever receive the amount of energy needed to move up energy levels?

Suppose there is a (blackbody) electromagnetic radiation source. It should emit a finite amount of photons every second with an intensity against frequency graph looking similar to a Maxwell Boltzmann ...
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0answers
19 views

Could ultrasound pings and triangulation really help de-scatter diffuse red light for imaging?

Does the science explanation in the latest OpenWater TED talk make sense in principle? The claim involves taking advantage of the doppler effect. Could someone give a more detailed explanation as to ...
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4 views

EM hf to uhf spectral irradiance

I wondered if any studies were done to monitor the total spectral irradiance of the radio spectrum integrated on area (earth surface) and over time (last century from the birth of radio ) of course, ...
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1answer
33 views

Is there a blackbody spectrum of photons inside a solid?

My initial guess yes there is a blackbody spectrum of photons inside a solid. The process that emits thermal photons won't "know" that it is deep inside a solid and not near the surface, so the ...
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2answers
76 views

How did Maxwell figure out the speed of light?

The Wiki article is about 2 graduate years of physics beyond my understanding. What is a good high-school rendition of his thought process: regarding his use of the "distributed capacitance and ...
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1answer
32 views

How cavity magnetron works?

I've found an explanation on explainthatstuff.com. There are these electrons from the cathode that are going around in a circle (because of the magnetic field), passing next to the cavities. Then it ...
3
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2answers
45 views

Propagation of mechanical waves in vacuum

It is known that, while electromagnetic waves can propagate in vacuum as they do not need a medium, mechanical waves (e.g. sound waves) cannot. However, vacuum has vacuum fluctuations, where (virtual)...
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1answer
100 views

What does Maxwell's equations predict for the propagation of EM waves converging to a point?

Maxwell's equations model EM radiation as propagating away from an accelerating charge. Suppose instead the propagation of this EM radiation is reversed and presented as a source-free boundary ...
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3answers
59 views

Polarisation of EM waves

My textbook reads 'The plane of polarisation of an electromagnetic wave is defined as the plane in which the electric field oscillates.' What exactly does this mean? I understand that an EM wave ...
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1answer
73 views

Why do we have to switch off mobile phones during flight in airplanes? [closed]

During take offs the flight attendant makes sure that mobile phones are switched off (or maybe turned in airplane mode), why is that necessary? (I suspect that there is something to do with physics ...
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1answer
21 views

Optical fibers field analysis, $\phi$ dependence not considered

In optical fibers, the core (with $\varepsilon = \varepsilon_1$) is usually represented by a cylinder of radius $a$, whose axis coincides with the $z$-axis in cylindrical coordinates. The cladding is ...
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2answers
51 views

Is the energy of an electromagnetic wave, in electron volts, an 'average' or a 'peak' value?

Since EM waves oscillate, is the energy given in eV an average or maximum value? In a related question, can a detector (of whatever sort) 'miss' an EM wave if the amplitude is at a minimum when it ...
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2answers
61 views

Fringes of equal inclination (Haidinger fringes) Why is the interference pattern circular?

From Hecht optics 5th edition: It says 'With an extended source, the symmetry of the setup requires that the interference pattern consists of a series of concentric circular bands centered on the ...
2
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2answers
97 views

Photons’ Speed (light speed) in vacuum [duplicate]

In a vacuum, are photons always traveling at 100% light speed? Can photons go any slower in vacuum? They have no mass which means they can go at 100% light speed, but do they have to?
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4answers
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Can you change the wavelength of light keeping frequency constant and can you do the opposite as well? [duplicate]

Can you change the wavelength of light keeping frequency constant and can you do the opposite as well? I understood the basics but please don't hesitate to go deeper into the concept. Also, If you ...
2
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1answer
30 views

What does classical theory predict about compton effect

I am currently studying Quantum Physics by Stephen Gasiorowicz. In the first chapter where he describes about compton effect, he says that According to classical theory, the mechanism for effect is ...
4
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1answer
46 views

Has a free neutron ever been shown to absorb/emit/interact with a photon?

Protons only 'interact with' very high-energy photons, whether inside a nucleus or free, right? I'm assuming the same about neutrons.... Neutrons have a small magnetic moment and a slight electric '...
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0answers
53 views

Is the speed of Magnetic field infinite?

My real question is: From Amperes law we know that there is no magnetic field outside of the coaxial cable because the magnetic field generated by the inner wire and outer shell are equal but in ...
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1answer
41 views

Visible light as fraction of the EM spectrum

I was asked today what percentage of the EM spectrum we can see. It looks like a simple question, and yet I don't know how to answer it. I know that the visible light has wavelengths between $3.8 \...
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1answer
49 views

Wire grid polarizer dimension

Why should the space between the wires be less than the wavelength of radiation in order for the polarizer to work efficiently?
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1answer
4k views

Why can’t you see at the start of the Big Bang?

I’m quite confused with regards to photon emission throughout the creation of the universe. From what I’ve heard, there was no light (of any frequency) in the universe until 300,000 years after the ...
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3answers
264 views

Are photons “born” travelling at the speed of light? In what manner do they propagate through space? [closed]

When an electron jumps from a high to a lower energy level and a photon is created, can the photon be detected from all vantage points or only from a discrete position? Does the atom nucleus cast a ...
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0answers
10 views

Resources for spin-stabilized magnets

I will be carrying out an experiment investigating the factors that effect the speed of a spin stabilized magnet. Can someone provide resources or articles that talk about/ have formulas related to ...
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4answers
118 views

If a photon doesn't experience time, how can it have a frequency? [duplicate]

It is said that photons, moving at c, do not experience time. But then, if a photon doesn't experience time, how can it have a frequency?
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Light is electromagnetic wave and it is a continuous stream of photon then why photon is not charge particle? [duplicate]

If photon is a charge particle then moving charge particle produces electric field and magnetic field but its not..
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1answer
42 views

EM propagation after leaving a wire having an alternating current

Initially, the changing electric field generates a magnetic field around a wire having an alternating current. The electric field and magnetic field travel outward from the wire at the speed on light....
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1answer
38 views

Strange strong interference/noise in radio waves [closed]

Good night, Since 2014 when I bought my car I use a FM transmitter inside it to play my bluetooth musics, to escape for every radio in city I put the radio to work in the highest frequency it works ...
2
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1answer
20 views

Electromagnetic radiation xrays

If x-rays are electromagnetic waves then why are they not deflected by electric and magnetic fields... As x-rays are electromagnetic they are having perpendicularly oscillating electric and magnetic ...
3
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0answers
40 views

How bright would cell phone towers appear to us if we could see in that range? [closed]

And how bright would a phone appear during a phone call or networking activity?
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3answers
118 views

Why doesn't electric field of an electromagnetic wave cause an electric shock?

An electromagnetic wave can have an electric field magnitude of more than 1000 V/m, which is a very high potential difference. When the light shines on you, why don't you feel an electric shock?
2
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2answers
123 views

How does the electron know to “release” the photon at the same angle at which it got absorbed? [duplicate]

This is a quote from Wikipedia: In classical electrodynamics, light is considered as an electromagnetic wave, which is described by Maxwell's equations. Light waves incident on a material induce ...
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0answers
16 views

Plasma Cyclotron Heating Textbook

I'm thinking of doing an independent reading course on the subject of cyclotron heating of plasmas, and I've love to hear any textbook recommendations. So far I've only found Gareth Guest's book, ...
1
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1answer
49 views

Quantum objects duality between waves and particles

i am reading an intresting book titled "Life on the edge: the coming age of quantum biology". And the subject of "quantum objects duality between waves and particles" takes a big part of this book. I ...
1
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1answer
28 views

Logarithms in uncertainties

I'm looking at the following plot: The vertical lines show the upper and lower frequency bounds for each of the bands W4, W3, W2...and I'm trying to convert them to wavelengths using $\lambda=\frac{c}...