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

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247 views

What symmetry is associated with conservation of Lipkin's zilch?

The 'zilch' of an electromagnetic field is the tensor $$ Z^{\mu}_{\ \ \ \nu\rho}=^*\!\!F^{\mu\lambda}F_{\lambda\nu,\rho}-F^{\mu\lambda}\,{}^*\!F_{\lambda\nu,\rho} \tag1 $$ given in terms of the ...
11
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1answer
295 views

How do higher-order optical chiralities look like?

The optical chirality of the electromagnetic field is a conserved quantity, analogous to the energy density, linear momentum density, and angular momentum density, which describes how chiral the EM ...
11
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3answers
508 views

Does radio use virtual photons?

In radio communication each accelerated electron in the transmitter antenna interacts with an electron in the receiver antenna by exchanging a photon. Is that photon always a virtual photon as ...
10
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2answers
1k views

If you run an electric current through a wire loop, do the accelerated charges radiate?

Does an accelerated charge always radiate? For example the current electrons in an electric circuit when moving through a turn they are accelerated, do they radiate because of that acceleration? If ...
9
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4answers
5k views

Radio antennas that are much shorter than the wavelength

From my limited experience with ham radio when I was a kid, I expect transmitting and receiving antennas to have lengths that are on the same order of magnitude as the wavelength, and in fact I recall ...
9
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4answers
4k views

Can radio waves be formed into a pencil beam?

Laser beams are said to have high "spatial coherence". This means that the beam is highly concentrated even at long distances (low spread). Can this be achieved with radio waves (much longer waves) ...
8
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1answer
110 views

Detailed form of light waves in vacuum and how to test it experimentally?

Consider a light wave in vacuum. Do the $\vec{B}$ and $\vec{E}$ fields have to be orthogonal to each other? Since you can add constants to a solution to Maxwell's equation it doesn't seem neccesary ...
7
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1answer
10k views

What is light, and how can it travel in a vacuum forever in all directions at once without a medium?

I know there are many questions that are similar (maybe identical?). I am not a physicist nor a student - I am just interested in physics and have been watching many physics channels on youtube ...
2
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1answer
382 views

accelerated charge in QED

Classical electromagnetism says an accelerated charge would radiate. Is this understood in QED? Is there QED derivation of Larmor's formula?
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3answers
1k views

Why is it hard to detect a black hole

I've read in some texts that we can't directly observe a black hole in space because not even light can escape from its gravity. Some of the indirect observational methods mentioned are, gravitational ...
7
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1answer
2k views

What’s the relationship between thermal radiation and Johnson thermal noise?

All objects above absolute zero emit radiation due to random collisions between the atoms they are made of. The spectrum of radiation emitted varies according to the temperature of the object, I ...
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2answers
2k views

Why is the photon emitted in the same direction as incoming radiation in Laser?

When an atom “lases” it always gives up its energy in the same direction and phase as the incoming light. Why does this happen? How can this be explained? How does the photon generated because of ...
6
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2answers
988 views

If photons move linearly, what's actually stopping them from passing through a microwave oven mesh?

So, my understanding is that the wavelength of a photon is the distance traveled in the time it takes it's magnetic field to oscillate. And it's inversely proportional to it's energy and it's ...
6
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1answer
3k views

What IS reflection?

How does quantum electrodynamics actually explain HOW reflection occurs on a microscopic scale? Note that Feynman's QED lecture series/book is not sufficient, as he only assumes that light DOES ...
5
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1answer
210 views

Why is the wave equation so pervasive?

The homogenous wave equation can be expressed in covariant form as $$ \Box^2 \varphi = 0 $$ where $\Box^2$ is the D'Alembert operator and $\varphi$ is some physical field. The acoustic wave ...
5
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1answer
685 views

Electromagnetic field of unpolarized light

I need help in finding an expression for the instantaneous electric and magnetic field of unpolarized light in order to write down and evaluate the time-averaged norm of the Poynting vector (i.e. the ...
4
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3answers
552 views

How to understand “accelerating charge radiate” using intuition? [duplicate]

While I know that accelerating charges produces EM radiations (at least in lots of cases), most discussion about this matter only focuses on which kind of situation will emit EM radiations and which ...
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3answers
3k views

Why does light in a room not form constructive and destructive interference patterns?

This is something that I have wondered for a long time. How come when I walk around why do I not see random black spots where light has collided destructively and bright spots where it has collided ...
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5answers
1k views

For an accelerated charge to radiate, is an electromagnetic field as the source necessary?

For an accelerated charge to radiate, must an electromagnetic field be the source of the force? Would it radiate if accelerated by a gravitational field?
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3answers
144 views

Does waving a magnet around create light?

If I wave around a bar magnet, the magnetic field in the space around it changes. Is this enough to go through the whole speed of light derivation implying that the motion creates an electromagnetic ...
2
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3answers
2k views

Exciting Surface Plasmon-Polaritons with Grating Coupling

I'm very new the topic of SPPs and have been trying to understand this particular method of exciting surface plasmons using a 1D periodic grating of grooves, with distance $a$ between each groove. If ...
2
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1answer
1k views

A two-level system absorbs a detuned photon. Where does the extra energy go?

Let's consider simple two-level system with frequency gap of $\omega_0$ between ground and excited state. Now, when we turn on external electromagnetic field with frequency $\omega < \omega_0$, ...
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1answer
655 views

What does a light wave look like (3d model)

What does a light wave look like? The only models I can seem to find online are 2D waves, they just look like sin() graphs. I have seen the models of the two components of "light waves" (electric ...
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2answers
741 views

If gravitational waves exist are they technically just another form of light/electromagnetic wave?

I would imagine a gravitational wave would have very similar characteristics to electromagnetic wave, what kind of differences are there?
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1answer
2k views

What is the relationship between Faraday cage mesh size and attenuation of cell phone reception signals?

This is related to the question how can electromagnetic waves reach a cell phone in faraday cage?, where in the answer it was stated that the holes (=size of the mesh) would need to be smaller than ...
9
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1answer
7k views

Why is black the best emitter?

Why are emitters colored black better emitters than other colors? Why is white a worse emitter?
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2answers
4k views

The energy of an electromagnetic wave

The intensity of an electromagnetic wave is only related to its amplitude $E^2$ and not its frequency. A photon has the same wavelength as the wave that's carrying it, and its energy is $h f$. So ...
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3answers
2k views

Should a Faraday cage block a radio's signal?

Today, I tried creating a very basic Faraday cage by surrounding a radio with two baking trays made out of iron. It didn't seem to affect the radio's signal (AM was being used, not FM). In theory, ...
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1answer
109 views

Electromagnetic Radiation of Charged particles

This question is motivated by similar one. If an accelerated point charge $q$ radiates with power $W$ then I assume the same particle with charge $-q$ will radiate with the same rate $W$. Now what if ...
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2answers
314 views

Is the wobbly rope depiction of a radio wave inherently wrong? And how do vectors of parallel waves align with each other?

I don't have a scientific education, yet I'm scientifically curious. Among other things, I'm struggling to understand the nature of electromagnetic waves. What I have recently realized is that the ...
2
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3answers
751 views

If I turn the light off in a room why does the light instantly disappear? [duplicate]

So today I was asked a question which I found very simple yet I honestly couldn't explain (embarrassingly). One of my mum's friends who knows I'm a scientist asked me "If I turn the light off in a ...
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1answer
105 views

What is the nature of the magnetic fields? [closed]

In this question, I am hoping to find out if there is an explanation to the magnetic hidden forces. In other words, what causes these fields? Is there any suggested theory, or any confirmed ones ? ...
1
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1answer
129 views

What is a wavelength of an EM wave physically?

This might be a silly question given I am a physics undergrad, but I was suddenly confused. Usually when EM hit a gap they diffract through the gap. But if the gap is too small, diffraction can't take ...
1
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1answer
222 views

Do electromagnetic fields gravitate?

It's well known that electromagnetic fields contains energy but do they gravitate ? When we talk about the composition of the universe it's now accepted that the 74 % is dark energy , the 22 % is ...
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2answers
95 views

How exactly do radio waves work?

So I understand that a radio wave is created by electrons oscillating in the antenna. But how does this create a radio wave? How are the electric and magnetic field "emitted" by the electrons? If you ...
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2answers
2k views

Why doesn't the magnetic field polarize when polarizing light?

If the magnetic field doesn't polarize does it follow the electric field path of propagation? or does it vanish?
6
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2answers
5k views

How photons represent colors that you see?

Right now, my understanding is that, a mixture of photons of many different frequencies is perceived as white by your eye. While no photons at all, is perceived as black. And photons with the blue ...
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2answers
392 views

What frequency photons are involved in mediating physical force?

If the force felt when pushing an object is mediated by the electromagnetic interaction and hence photons, what is their frequency?
4
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1answer
191 views

How does the Cosmic Microwave Background give us information about the Big Bang?

I was reading about CMB after this new breakthrough last week and I could not figure this out. The CMB did not exist before the epoch of Last Scattering. They were just photons which were formed at ...
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1answer
205 views

Why is there an emission of gamma rays?

When a spontaneous radioactive reaction happens, there is an emission of gamma rays (in most cases) What causes this emission?
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2answers
725 views

Mirror problem of radiation pressure

If two perfect mirrors are placed facing one another and they are in proximity, and photons (don't ask me how) are traveling between them and toward one of them, what is to keep the radiation pressure ...
4
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1answer
3k views

Force on Earth due to Sun's radiation pressure

I have been asked by my Classical Electrodynamics professor to calculate the force that the Sun exerts in the Earth's surface due to its radiation pressure supposing that all radiation is absorbed and ...
3
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0answers
114 views

Dispersion of light in metals and the plasma frequency

I've been reading about the dielectric function and plasma oscillations recently and I encountered the following dispersion relation for EM waves in metals or in plasma (Is it correct to treat those ...
3
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2answers
223 views

When light is only considered as a particle, is it still considersed to be oscillating electic and magetic waves?

I have my head around wave-particle duality, however people tend to refer to light as either a wave or a particle in different situations. If I were to consider light as a particle am I still ...
2
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1answer
159 views

does photon travels in a helical path in an optical vortex?

The wave front of the optical vortex beam is helical. Does it mean that the photon travels in a helical path? When the optical vortex beam is focused on a screen, an annular ring with dark center is ...
2
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2answers
658 views

Why is the Luminiferous aether theory wrong? [closed]

I saw on this page about the constant speed of light that there are two ways of interpreting this constant speed: General relativity The Luminiferous aether theory I understand why the theory of ...
2
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3answers
2k views

How could electromagnetic waves propagate through space although they have no electrons?

How could electric fields in these waves propagate through space although in space there's no electrons for the electric field to be formed? is there another type of charged particles that carry the ...
2
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2answers
2k views

Continuous vs. Discrete Spectra in various materials

I read that the reason solids emit continuous spectra is that they don't have time to let their electrons decay-they are too close together. Given that electrons decay on the order of 100 nanoseconds ...
2
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0answers
929 views

The physical meaning of electromagnetic wave

What, fundamentally, is an electromagnetic wave? As far as I know, all wave phenomena are derivations of an oscillating processes, e.g. particles vibrating in a medium. I can't imagine a wave process ...
2
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1answer
404 views

How is it possible that we see light from shortly after the big bang?

How can astronomers see light from shortly after the big bang? How did we get "here" before the light that emanated from our "creation"?