Propagating solutions to Maxwell’s equations in classical electromagnetism and real photons in quantum electrodynamics. A superset of thermal-radiation.

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3
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1answer
124 views

Why one should follow Snell's law for shortest time?

whenever two media and two velocities are involved, one must follow Snell's law if one wants to take the shortest time. Why snells law must be followed to travel diffrent media in shortest time? ...
2
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1answer
48 views

Does amplitude of electric field and magnetic field vary with distance in em waves?

Does the amplitude of electric field and magnetic field of an em wave vary with distance?
1
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0answers
58 views

advantages/disadvantages of a cylindrical microwave oven cavity in comparison to a rectangular cavity

Why are rectangular cavities preferred for standard microwave ovens with a frequency of 2.45 Ghz? What is the reason that you can hardly find a circular cavity? What are the disadvantages of ...
0
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0answers
24 views

What is the physical meaning of a magnetic conduction current?

In electrodynamics, it is possible to have an electric conduction current, whereby $J=\sigma_e E$, with $J$ being the current, $\sigma_e$ the electrical conductivity and $E$ the electric field (this ...
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2answers
52 views

If I spin an electromagnet do I create a stationary electromagnetic wave? [closed]

Since its the same fundamental forces I would imagine it would. Or, is it radiating the waves and it would only look like a stationary "wave"?
2
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3answers
97 views

How do Black Bodies Absorb and Emit Radiation? [duplicate]

I have learnt how the gases of elements are able to absorb only certain wavelengths of EM radiation corresponding to the energy transitions between energy levels of orbitals. Furthermore, these ...
-1
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1answer
68 views

How I can prove refractive index in an environment is this? [closed]

in "Applied Quantum Mechanics" by A.F.J. Levi, is a problem that I couldn't solve it can any solve it: if electrical filed is: $$ \mathbf{E}\left(\mathbf{r}, \omega \right) =\mathbf{E}_{0}\left(\...
0
votes
2answers
67 views

Why do UV lamps look purple?

UV radiation isn't visible to the human eye, so how come we can see it as a purple/violet light from a UV lamp? Is it just because the lamps aren't perfect and end up emitting some light at a higher ...
36
votes
4answers
5k views

How to imagine WiFi signal propagation?

When thinking about how the WiFi signal propagates through a household, can I use the following thought experiment? Assume absolute darkness. Place a strong lightbulb where the WiFi access point ...
0
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2answers
49 views

Explanation of ray caustics in E&M

My understanding (now) of a real caustic is that it is envelope of curves or ray-paths that arise due to reflection or refraction from the medium/manifold. My main question is, I am seeing the term "...
0
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2answers
43 views

Why doesn't the group velocity of a plasma EM wave equal the phase velocity here?

For plasma EM waves we have the dispersion relation $$\omega^2=\omega_p^2+c^2k^2$$ where the plasma frequency $$\omega_p^2=\frac{n_e e^2}{\epsilon_0 m_e}$$ One can show that $v_p v_g=c^2$, i.e., the ...
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1answer
47 views

Why do High Pressure Gases produce a Continuous Spectrum?

I am aware that low pressure/density gases produce an emission spectrum as there are specific energy transitions that the electrons can make, emitting certain frequencies of EM waves. However high ...
0
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0answers
49 views

Why is the satellite dish still needed?

How much does it amplify the signal? The receiver cannot pick up the signal without the dish? Is it possible that it will disappear in 10 years? As the sensitivity of the receiver is enhanced? ...
3
votes
2answers
82 views

Does a source of photon emission “sense” if the photon is absorbed? [closed]

Can the absorption of a photon be 'felt' by the source that emitted it? At least, if we assume that it emits a steady stream of photons? Is there a back reaction of some kind on the source?
0
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1answer
35 views

Why don't conductive objects change color when electric dipoles are induced in them?

I was playing around with a comb, my hair, and pieces of paper when it occurred to me that inducing a dipole on the pieces of paper meant that many valence electrons previously on the side closer to ...
0
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1answer
62 views

How do electromagnetic waves/light travel at the speed of light?

When something reaches the speed of light, then time is said to stop, or at least is perceived to have stopped. The reason is that at that speed, the object become infinitely heavy and requires ...
-1
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1answer
26 views

Reflection and angle of refraction

Does the angle of refraction depend on the properties of the material if the angle of the incidence is the same for two different materials? Say I shed light on a surface with angle $ \theta $ and ...
0
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0answers
18 views

Electromagnetic Wave Impedance

In a derivation of the transmission and reflection coefficients for light incident at an angle onto a surface where we have a change in refractive indices the proof says that $$\frac{E}{H}=\frac{Z_0}{...
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2answers
51 views

How does always the magnetic field lag the elctric field in a conductor?

In conductor, the relation between the phase of the magnetic field $\delta_B$ and that of the electric field $\delta_E$ is given by $$\delta_B-\delta_E=\tan^{-1}(\frac{\beta}{\alpha})$$ where $\alpha$ ...
7
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0answers
91 views

Why is it that fractal antennas can filter out so many frequencies?

As known, fractal antennas are used for example in cell phones. But why is it that so many different kinds of frequencies can be filtered out of the forest of radio waves surrounding us? Is it because ...
1
vote
1answer
111 views

'Hovering' light rays on the edge of a black hole

According to Prof. Hawking, light rays will 'hover' on the edge of a black hole. If this is true, and the light 'stops' on the edge, how can the electric/magnetic fields which, constitute the light, ...
0
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0answers
32 views

Propagation Of Wave in Rectangular Waveguide

From what I understand, electric and magnetic fields are perpendicular to one another and the direction of wave propagation.The text book states that the direction of wave propagation in the ...
0
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1answer
15 views

Methods to ioniz air molecules

What are other alternatives ways to ionize air molecules, except the electric field charging and the use of the so-called corona discharge?
0
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0answers
40 views

Electromagnetic field produced by a charge?

I guess vibration of a charge particle produces vibrating EM wave and oscillation of a charged particle will produce oscillating EM wave. If charge is only accelerating (speeding up) what will happen ...
0
votes
1answer
38 views

What are the experimental results of neutron -neutron scattering?

I'm curious about does a neutron - neutron scattering (if such an experiment was carried out) is an in elastic process or is it accompanied by energy losses. Additional question: What is the energy ...
8
votes
3answers
663 views

Speed of gravitational waves vs speed of light

I own an educational YouTube channel on physics and astronomy. I am currently working on a gravitational waves video extension to my "How Fast Is It" video book on relativity theory. I have a question ...
0
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2answers
75 views

What is beyond Gamma Rays and Radiowaves in the Electromagnetic Spectrum?

The electromagnetic spectrum is commonly refered to as consisting of; Radio-waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, Gamma Rays - of increasing frequency from left to right. ...
5
votes
3answers
53 views

Why are pulsar's radiation beams collimated?

Every picture of a pulsar a see shows a very collimated radiation beam. What is the mechanism generating such a collimation? Note: I am not talking about "relativistic jets". I am talking about ...
11
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4answers
530 views

Are EM radiation and EM waves the same thing?

Are EM radiation and EM waves the same thing? I have seen this topics treated separately in many books. It is still not clear to me whether EM radiation and EM waves are synonymous. Is there any ...
3
votes
1answer
72 views

Difference between radio waves and other electromagnetic waves?

Yes radio waves have different frequency and wavelength than others but it seems that radio waves are produced by sinusoidal current while other electromagnetic waves do not need need sinusoidal ...
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2answers
127 views

Compton Effect Explanation

Can someone brief me about Compton effect and why does this happen? I searched everywhere read a CERN article too but couldn't understand it.
0
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1answer
25 views

Laser vs Transmiting antenna

Ok so this will probably will sound stupid to you but please put an effort into elaborating with my train of thought thank you :) For no particular reason this question popped in my head: People ...
0
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0answers
41 views

Frequency of Electromagnetic Radiations/Waves?

"A charge that is accelerated will produce variable electric and magnetic fields. These are electromagnetic waves. If the charge oscillates with a frequency f, then the resulting EM wave will have a ...
1
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1answer
32 views

Charge affected by EM-pulse. What is the equation of motion?

I'm studying for my test on radiation for Tuesday. I came across this exercise. Thought it looked interesting but now I'm stuck and I can't move forward before I finish this one. Exercise: A ...
0
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0answers
24 views

The radiation intensity considering dipole, quadrupole and magnetic dipole parts

In page 204 and page 205 of the book "The Classical Theory of Fields" written by Landau and Lifshitz, there is this sentence In averaging the square of the magnetic field, all the cross-products ...
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0answers
21 views

Huyegns Principle and data transmission

Huygens's principle (The Gist) states that for every object on which light is incident every point on that object acts a light source till light is being incident on it. So is it possible than WiFi ...
17
votes
4answers
2k views

Same photon or different photon?

Consider a typical optical focusing system: A small light source, then a collimating lens, then a focussing lens, and then a detector (e.g. CCD). Assume that source intensity is so low that only one ...
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3answers
48 views

Frequency of other light in white light [closed]

I have this question in mind because I read that the frequency of light depends only on the source of light. If we consider a source of white light then it emits light of different colours also. Then ...
0
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1answer
55 views

Do all solid objects emit visible light?

Are there solid objects that do not emit visible light? To my limited and humble knowledge, creating such an object would require us to "only" shift the spectrum of emitted radiation. Is it possible? ...
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0answers
16 views

What wavelengths of electromagnetic radiation are emitted by the LH2/LOX reaction?

Rocket engines such as the Rocketdyne Rocket System 68 and the Space Shuttle Main Engine use liquid hydrogen and liquid oxygen as propellants. The exhaust from this type of engine is notable in ...
7
votes
4answers
260 views

How do electromagnetic waves carry energy?

Its said that electromagnetic waves carry energy. Is this because these waves are made up of electric and magnetic fields which can cause changes to the stuff that falls with in their range? Is that ...
4
votes
2answers
167 views

Nature of light in Special Relativity

What is the nature of light in the context of Special Relativity? Is it a photon, or an electromagnetic wave, or something else? I have doubts, because a photon seems to me a quantum mechanical ...
10
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6answers
2k views

Light's inverse square law: Does it require a minimum distance from the source?

Does the inverse square law begin to take effect the moment light leaves its source? For example, does light's intensity decrease, i.e. does the area in which the photons might land increase, at a few ...
0
votes
1answer
48 views

What does it mean physically to set $\exp(ikr)=1$ in the dipole approximation?

In the dipole approximation one sets the $exp(ikr)=1+ik.r+...=1$. ($|<f|exp(ikr)\epsilon.r|i>|^2$). Which makes $k.r=0$. What does it mean physically? Is the plane transverse wave converted to ...
1
vote
3answers
112 views

Does an electromagnetic wave necessarily contain many photons? [duplicate]

I've often come across people saying from a quantum physics standpoint that an electromagnetic wave necessarily contains many photons. But doesn't the double-slit experiment conducted one photon at-a-...
3
votes
4answers
144 views

Why can't the wave model for radiation account for the photoelectric effect?

While I understand the effect of varying wavelength and frequencies on the photoelectric effect, I can't seem to turn my mind around that question... I suspect it has to do with quantas and the non ...
2
votes
0answers
39 views

Plasmon quenching vs plasmon decay. What is the difference?

I'm reading an article "Quenching, Plasmonic, and Radiative Decays in Nanogap Emitting Devices" (pubs.acs.org/journal/apchd5). I don't understand the following: Counterintuitively, we evidence ...
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0answers
11 views

When light reflects from a medium of lower index of reflection to a medium of higher index of refraction, why does the light undergo a phase shift? [duplicate]

I learned in my physics class that there is a phase shift when light reflects off a low $n$ from a higher $n$, but never got the explanation.
0
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1answer
29 views

Can you have a problem with a Dirichlet boundary condition but with waves that reflect off the boundary?

Say we are looking for a solution to the Helmholtz equation $$(\Delta + k^2) u = 0,$$ in in the upper half space ($y > 0$) in 2D with a Dirichlet boundary condition on the $x$-axis, that is, $u(x, ...
0
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0answers
10 views

Change in Q factor on tuning external magnetic field in Electron spin resonance experiment

Does the Q factor of the cavity resonator show a dip at the resonant value of the external magnetic field while performing an ESR experiment?If so, what is the physical reason behind it?