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

learn more… | top users | synonyms (2)

2
votes
3answers
2k views

How is electromagnetic wave variation distributed in space?

Imagine an electromagnetic wave (a monochromatic one for example). The electric field amplitude and its variations travel in the propagation direction. So, if there really exists a propagation ...
1
vote
3answers
117 views

What is an EM wave? [closed]

How does an EM wave carry energy? What is an EM wave? (Is it a collection of photons?) What are the mechanics behind it? I am an engineer and I've been taught to think of light (light is my area ...
1
vote
2answers
702 views

Why do waves diffract?

There have already been a lot of questions on this site on diffraction but I still believe this one might be slightly different. In electromagnetic waves, diffraction and any other phenomenon of wave ...
1
vote
1answer
394 views

Retarded potential in gravitational field?

Is there a retarded potential concept in gravitational field similar to electromagnetic radiation?
1
vote
1answer
1k views

Can electromagnetic radiation (i.e. photons) produce gravity? [duplicate]

I don't want to play with physical laws in a frivolous way. Assuming that the nature of matter and energy is the same, can a high density of highly energetic photons produce a gravity force? We do ...
0
votes
1answer
50 views

Does slowing light violate relativity?

Last year Scottish scientists managed to slow down photons in vacuum by changing their shape. Does this violate the special theory of relativity?
-2
votes
4answers
2k views

Electro Magnetic Waves can cause matter displacement?

After watching this video: http://www.youtube.com/watch?v=j1jIjx0XF_U The experience is made with a speaker that generates a sound wave or mechanic wave. Can you use this to establish a link to ...
65
votes
3answers
8k views

Why doesn't the motion of a car affect the frequency of radio stations?

When we go in a car and tune to an FM radio station, why doesn't our motion disturb the frequency? Like the Doppler effect?
14
votes
2answers
26k views

Why is Near Field Communication (NFC) range limited to about 20cm?

Near Field Communication (NFC) operates at 13.56 MHz. Near Field is the region situated at a distance r << λ λ = c/f ...
21
votes
3answers
2k views

Can light exist in $2+1$ or $1+1$ spacetime dimensions?

Spacetime of special relativity is frequently illustrated with its spatial part reduced to one or two spatial dimension (with light sector or cone, respectively). Taken literally, is it possible for ...
21
votes
5answers
2k views

Can a photon get emitted without a receiver?

It is generally agreed upon that electromagnetic waves from an emitter does not have to connect to a receiver, but how can we be sure this is a fact? The problem is that we can never observe non ...
14
votes
2answers
492 views

Do accelerated charges radiate or not?

This questions has been asked all over the net (here included) but I can't find a satisfactory answer or discussion. Some say it does not radiate if the acceleration is caused by a uniform gravity ...
8
votes
1answer
143 views

Optical chirality and its possible hierarchy of generalizations

Optical chirality refers to a constant of motion of the electromagnetic field, which measures in some sense how chiral a light field is. Specifically, the pseudoscalar quantity $$ ...
3
votes
1answer
5k views

Optical constants of noble metals: the Drude model for microwave modelling

I have a question regarding the optical constants of noble metals. According to Johnson and Christy's paper Optical Constants of Noble Metals (Phys. Rev. B 6, 4370–4379 (1972), ...
14
votes
1answer
896 views

Why is everything not transparent? [duplicate]

There is a related question on this site here: Why glass is transparent? Which explains that glass is transparent because the atoms in glass have very large energy differences between energy levels ...
9
votes
3answers
5k views

Properties of the photon: Electric and Magnetic field components

Consider an electromagnetic wave of frequency $\nu$ interacting with a stationary charge placed at point $x$. My question concerns the consistency of two equally valid quantum-mechanical descriptions ...
6
votes
3answers
6k views

How can I determine transmission/reflection coefficients for light?

When light rays reflect off a boundary between two materials with different indices of refraction, a lot of the sources I've seen (recently) don't discuss the relation between the amplitude (or ...
15
votes
3answers
2k views

Why is the bottom part of a candle flame blue?

What’s the explanation behind the bottom part of a candle flame being blue? I googled hard in vain. I read this. I don’t understand how it’s explained by the emission of excited molecular radicals in ...
14
votes
7answers
9k views

Why does light change direction when it travels through glass?

This was explained to me many years ago, by a physics teacher, with the following analogy: "If someone on the beach wants to reach someone else that is in the water, they will try to travel as much ...
12
votes
3answers
1k views

What is meant by the temperature of the CMB?

This is what I commonly read: The CMB came to existence when atoms where formed and photons weren't constantly absorbed anymore. In other words, the universe became "transparent". Because of the ...
12
votes
3answers
1k views

Can the speed of light become complex inside a metamaterial?

The speed of light in a material is defined as $c = \frac{1}{\sqrt{\epsilon \mu}}$. There are metamaterials with negative permittivity $\epsilon < 0$ and permeability $\mu < 0$ at the same time. ...
11
votes
4answers
2k views

Is it possible to shield a camera so as to record from the inside of a running microwave oven?

Would it be possible to create shielding for a camera, allowing it record food being cooked from the vantage point of the inside of a consumer microwave oven without the camera being damaged? ...
6
votes
5answers
2k views

Why are electromagnetic waves called waves even though they don't travel through a medium?

If waves are defined as the oscillation of a medium, why are electromagnetic waves called waves as they do not need a medium to travel through?
6
votes
2answers
2k views

Is the de Broglie wavelength of a photon equal to the EM wavelength of the radiation?

Is the de Broglie (matter) wavelength $\lambda=\frac{h}{p}$ of a photon equal to the electromagnetic wavelength of the radiation? I guess yes, but how come that photons have both a matter wave and an ...
6
votes
2answers
822 views

Microwave oven + water: dielectric heating or ion drag?

When you place a water or food in a microwave oven, it heats. Which process commits more energy to that: dielectric heating, or ion drag i.e. resistive heating? AFAIK, in distilled water (which is a ...
5
votes
2answers
234 views

Is a Perfect/Lossless Mirror possible?

In traditional mirrors, some of the input light is absorbed by atoms in the mirrors surface and are 'lost' as heat, degrading the quality of the reflected image. Could this loss be compensated by an ...
4
votes
4answers
2k views

Do Electromagnetic Waves really propagate through continuous Induction?

I've often seen it said that in an Electromagnetic Wave the changing Electric Field component creates the Magnetic Field Component and the changing Magnetic Field Component in turn creates an Electric ...
3
votes
4answers
4k views

Bohr's model of an atom doesn't seem to have overcome the drawback of Rutherford's model

We, as high school students have been taught that-because Bohr's model of an atom assigns specific orbits for electrons-that it is better than Rutherford's model. But what Rutherford failed to explain ...
2
votes
4answers
1k views

Non-complex proof that the electric and magnetic fields are perpendicular in a plane wave

I'm looking for a proof that the electric and magnetic fields in a plane wave are perpendicular that doesn't invoke complex E and B fields. I haven't been able to find one. If the proof requires ...
9
votes
3answers
7k views

In electromagnetic radiation, how do electrons actually “move”?

I've always pictured EM radiation as a wave, in common drawings of radiation you would see it as a wave beam and that had clouded my understanding recently. Illustration on the simplest level: ...
8
votes
3answers
1k views

Why use lasers for intense, localized heat instead of some other light source?

Lasers are used in various industrial processes that need intense, localised, heat (3d printers and laser cutters come to mind). My question is: why use lasers? There are many other (cheaper, ...
8
votes
2answers
795 views

Do human bodies give off a consistent but unique radiation/electromagnetic/energy signature?

Is there any facet of the energy emitted by a human body that is consistent and unique - like a fingerprint, but a signal that could be detected by a remote device?
7
votes
2answers
499 views

Measurement of blueshift from Andromeda galaxy

How the blueshift from Andromeda galaxy was measured? Since the measurement of blueshift/redshift has to do with the identification of relative distance of spectral lines how this identification is ...
7
votes
1answer
1k views

If fields die off proportional to R^2, why does light keep going?

Why does light continue on forever if it was created from some source whose radiation dwindles at a rate of the inverse square of distance. Clearly light can be viewed as an interdependent phenomena, ...
7
votes
6answers
14k views

How many colors exist?

How many "colors" do exist? Our perception: As far as I know, colors are just different frequencies of light. According to wikipedia, we can see wavelengths from about 380 nm und 740 nm. This means ...
7
votes
3answers
1k views

Can we transport energy over infinite distances through vacuum using light?

I know that light (or electromagnetic radiation in general) attenuates in intensity as the square of the distance it travels. Why does it attenuate? Are the photons being scattered by the medium ...
5
votes
2answers
1k views

Why is glass much more transparent than water?

There is a related question (Why glass is transparent?) but I am coming at it only from Maxwell's equations. One can determine the skin depth $δ$ for poor conductors like (pure) water and glass using ...
5
votes
4answers
7k views

Can anyone explain to me why light is not dispersed into a spectrum through a parallel glass slide, but only through a prism?

The question pretty much sums up what I need to know. Why is it that light only gets dispersed into a spectrum when travelling through two non-parallel sides(like a prism) and not through something ...
5
votes
1answer
254 views

Is the number of wavelengths of light spanning a distance invariant with respect to spacetime distortion?

I was recently asked by a friend how the expansion of spacetime affects photons. I gave him what I feel is a satisfactory general response, but it got me wondering how, exactly to calculate this ...
5
votes
4answers
9k views

Light emitted by an object according to its temperature

According to this picture the light emitted by an object depends on its temperature. That makes perfect sense when we heat a metal. As its temperature raises we see it red at first, then orange, ...
4
votes
4answers
6k views

How does radio receives signal from particular station?

When you tune your radio (digital or analog) to receive say 100 MHz frequency and while in the environment there are hundreds of channels everywhere around the radio. How does it chooses to receive ...
4
votes
4answers
607 views

Exactly how is the constant measured velocity of light deduced from Maxwell's equation?

For electromagnetic radiation the velocity of propagation is $c = 1/\sqrt{\mu_0 \epsilon_0}$. Since both $\mu_0$ and $\epsilon_0$ do not vary in any inertial frame, then $c$ must be constant in any ...
3
votes
1answer
207 views

Refraction: Energy flow, tunneling and Evanescent EM waves

In the full internal reflection case where we have a refracted evanescent wave, If another object is nearby, then we could have wave tunneling phenomenon(frustrated total internal reflection). I am ...
3
votes
2answers
191 views

Is there one all encompassing electromagnetic field? Or are electromagnetic fields separate and individually generated?

Many people have been using very confusing and sometimes contradictory language when describing electromagnetic fields and electromagnetic radiation. It's going to be hard to word this question so ...
3
votes
1answer
247 views

Which green spectral line(s) are emitted in a Thomson tube?

Related: What is meant by boiling off electrons in a heater coil? In the Thomson tube we used in our class to produce an electron beam, the lab manual stated that the tube was filled with a low ...
3
votes
1answer
778 views

Why electron clouds in atoms don't radiate? [duplicate]

I was reading that Bohr assumed electrons in orbit simply did not radiate, and my professor told me that the actual case is that electrons are clouds of probability. Even so, aren't they still moving ...
2
votes
1answer
79 views

If EM waves are not physical, positional waves (on a X,Y,Z axis), why does interference pattern appear positional?

I have read that EM waves propagate in straight lines: https://van.physics.illinois.edu/qa/listing.php?id=17699 Wherein the only the electric (E) and magnetic (B) fields to change (or oscillate) at ...
2
votes
1answer
477 views

why is advanced radiation absent?

the Lienard-Wiechert green functions have future and past null cones of radiation. Maxwell equations allow for a continuous range of mixtures between the retarded and advanced components, but we have ...
1
vote
2answers
133 views

Would passing horizontally polarized light through a varying width vertical slit allow you to measure the positional (x) amplitude of light? [duplicate]

I have found closely related questions on StackExchange, but (surprisingly) not this exact question. Seems some answers say individual photons do not have amplitude, only when traveling with other ...
1
vote
2answers
428 views

Why doesn't an electromagnetic wave violate conservation of energy?

I'm starting to study electromagnetic waves and as i understand, an electromagnetic wave projects a varying electric field. This electric field can in turn give forces of repulsion/attractions to the ...