Propagating solutions to Maxwell’s equations in classical electromagnetism and real photons in quantum electrodynamics. A superset of thermal-radiation.
2
votes
1answer
155 views
Does a magnetic field have gravity?
Re-reading http://physics.stackexchange.com/a/33156/5265; I find myself thinking if light, being EM in the humanly visible spectrum, may possess gravity - does a magnetic field also possess gravity?
0
votes
1answer
137 views
What is the ion drag mechanism in dielectric heating?
While reading about dielectric heating on Wikipedia, I read about the ion drag mechanism but there wasn't enough information about.
I know there is another Phys.SE question talking about the ion drag ...
1
vote
1answer
68 views
How does the specific frequency of EM Radiation relate to displacing electrons from their orbits?
I've only a general grasp on how all this works, so it could be I'm asking this poorly or misunderstanding what happens. With that said:
The energy of EM radiation is a function of its frequency. ...
3
votes
2answers
200 views
Radio communication and antennas
I'm trying to understand how an antenna is able to understand, but have a few quesions:
I understand that for an antenna to distinguish between 2 (or more) signals, they have to be in different ...
3
votes
1answer
166 views
Does $\lambda\nu = c$ hold for all the waves in the universe?
Are all waves in the universe the same as electromagnetic waves?
Basically, my question arises from an equation I found in my chemistry textbook:
$$\lambda \nu ~=~ c.$$
This states that the ...
15
votes
11answers
4k views
Why is light called an 'electromagnetic wave' if it's neither electric nor magnetic?
How can light be called electromagnetic if it doesn't appear to be electric nor magnetic?
If I go out to the sunlight, magnets aren't affected (or don't seem to be). And there is no transfer of ...
0
votes
0answers
89 views
Wireless signal strength
My question is possibly somewhat misplaced, but I'll try to explain as best as I can. Suppose I have a transmitter with a frequency of 2500MHz and a power of 1W. It radiates uniformly in all ...
0
votes
1answer
63 views
Does every wavenumber of IR result in a different kind of vibration?
Does every wavenumber of IR result in a different kind of vibration?
If that is true, what if a molecule absorb 2 different wavenumbers (which cause different rocking and symmetrical stretching for ...
2
votes
2answers
112 views
Power due to dipole radiation and time reversal symmetry in classical E&M
The dipole formula for the power loss emitted by a time varying electric dipole is (in natural units) $P = \frac{\dot d_i^2}{6 \pi}$. This is clearly even under time reversal symmetry $T$, but a ...
0
votes
0answers
114 views
Antenna Power and gain calculation [closed]
I have a wireless security related question, the second part confused me:
Your wireless network usually has a range of 100 feet. However you
are having a (confidential) meeting in a 10’ x 10’ x ...
2
votes
1answer
71 views
Could we really charge metal plates using microwaves?
While skimming through Dielectric heating, I read that they use microwaves to charge the plates. How do they do that?
0
votes
3answers
71 views
What kind of “camera” and “light” source should I use to detect the path along which the light moves?
I would like to have an image ( in any kind of space ), where I see the path of a "light" source. In my understanding the most common, directed source would be a laser pointer.
...
1
vote
1answer
178 views
Velocity of electron in electrostatic field. Does radiation matter?
There's a voltage difference of 1000 Volts between two points 2 meters apart. An electron starts at the point of lower potential and is left to travel alone in a straight line until it reaches the ...
0
votes
0answers
20 views
Why can radio wave travel through walls while imfrared can't? [duplicate]
Possible Duplicate:
If both radio waves and gamma rays can travel through walls
Does it have anything to do with the materials used to build the wall?
What determines if a material can ...
0
votes
0answers
52 views
Electromagnetic charge [duplicate]
Possible Duplicate:
If electromagnetic field give charge to particles, does photon carry charge?
Is it possible to charge photons
I was wondering if light when it's in wave form (seeing ...
5
votes
2answers
109 views
Xray compression of secondary in hydrogen bomb
Accounts of the "secret" of the hydrogen bomb describe Xrays from a primary fission explosion reflecting off of the bomb case (occasionally passing through polystyrene foam) and compressing and ...
3
votes
3answers
164 views
What if $\gamma$-rays in Electron microscope?
I was referring Electron microscopes and read that the electrons have wavelength way less than that of visible light. But, the question I can't find an answer was that, If gamma radiation has the ...
0
votes
0answers
131 views
Transmission formula for two near field polarizing filters?
Consider two parallel wire "comb" filters oriented at 45 degrees relative "tooth" angle.
The comb tooth spacing spacing is much less than one wavelength, and the comb tooth length is much more than ...
2
votes
2answers
340 views
What's the Significance of Color Changes Between EM-Spectrums?
As everybody knows that Black objects are black because almost all the light that falls on them is absorbed into the material. Little or no light is reflected back toward our eyes, therefore we see ...
1
vote
1answer
72 views
1MeV ray hits a band gap of 2eV : trying to understand X-rays
I am trying to understand why radio waves pass though the human body, light does not, but X-rays still pass.
In my mind I imagine that radio waves don't supply enough energy and don't excite any ...
1
vote
0answers
251 views
What happens with photon when it is slowed down substantially?
In a dispersive media light's velocity can change substantially. Imagine we can slow it down to near 0 what the wave would look like?
Frequency of light does not seem to change even at v=0 (at least ...
6
votes
5answers
813 views
Why is Light invisible?
Why can't we see light? The thing which makes everything visible is itself invisible. Why is it so?
1
vote
2answers
211 views
Quantum Mechanics- Antenna emitting electromagnetic radiation
Radio signals are being transmitted in a frequency of $ 8.4 \times 10^9 s^{-1} $ and being received by an antenne that is capable of receiveing power of $ 4 \times 10^{-21} watt $ ($ 1 watt = 1 J ...
0
votes
0answers
42 views
EM-wave hits a brick-wall, $\pi/2$ -phase-shift? [duplicate]
Possible Duplicate:
Phase shift of 180 degrees on reflection from optically denser medium
If I have a cord-wave, I get a phase-shift with attached cord but do I get such a phase-shift with ...
0
votes
2answers
318 views
Is it true looking at an object from a great distance with a telescope will show the past version of the object?
Once again from my son's workbook.
It discussed standing on a planet 65 million light years away from Earth, with an extremely powerful telescope pointed at Earth. It claimed that then you could see ...
2
votes
1answer
128 views
Where are the harmonics in the radio spectrum?
When I strike a string on my guitar and look at the audio spectrum, I can see the fundamental frequency as a large peak. I can also see the harmonic frequencies as a train of little peaks at ...
2
votes
2answers
320 views
What is the difference between Quantum teleportation and Radio waves?
Quantum teleportation over 143 kilometres using active feed- forward
What is the difference between Quantum teleportation and radio waves?
2
votes
0answers
87 views
Macroscopic chromodynamics
Lately I've been reading about gamma ray lasing phenomena, and I've been wondering about the applications of this.
More concretely, the above fantastic question led me to wonder if we could somehow ...
-1
votes
1answer
404 views
Oscillating Dipole: Principle of Receiving and Transmitting Electromagnetic wave?
I am practising to Tfy-0.1064 -elementary-physics-exam and doing this practise -exam here. The problem in Finnish goes like this:
"Selosta lyhyesti sähkömagneettisen säteilyn lähettämisen ja ...
5
votes
4answers
524 views
How is wireless communication possible?
Like all my questions, I fear this will be very naive, because my physics background is very limited. Please bear with me.
I think of the electromagnetic field as a section of a vector bundle over ...
6
votes
1answer
234 views
Why is there a photon every millimeter on earth coming from a star millions of light years away?
I've been having this confusing thought for so long now it would be amazing if someone could answer me.
Imagine this asterisk * . As you see, from the center point, lines go outwards, just like a ...
2
votes
3answers
184 views
What makes Poynting's theorem consistent for a charge moving in a static electric field?
Poynting's theorem is given by
$$\frac{\partial}{\partial t}\int_{v}Udv
+ \oint_{A}\vec S\cdot \vec {dA}
+\int_{v}\vec E\cdot\vec J dv
=0
$$
Where,
the total electromagnetic energy inside the ...
2
votes
3answers
510 views
Reflection of Electromagnetic Waves
Visible light - Being an Electromagnetic wave is reflected by glass (take mirror). Would all other waves in the electromagnetic spectrum be reflected in the same way by our simple mirror... For highly ...
2
votes
2answers
207 views
Origin of Electromagnetic Interactions between Molecules
What is the origin of electromagnetic interaction between molecules? Anyway, it should have some relation with atoms. Also, These electromagnetic interactions are playing a major role in different ...
2
votes
1answer
322 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 ...
3
votes
1answer
580 views
Why can glass absorb ultraviolet light?
Please see the following photos. (I cannot post them...)
http://i1163.photobucket.com/albums/q554/startanewww/CIMG4545.jpg
http://i1163.photobucket.com/albums/q554/startanewww/CIMG4546.jpg
From the ...
0
votes
3answers
282 views
Why do photons travel?
Photons travel at the speed of light.
Is there a known explanation of this phenomenon, and if yes, what is it?
Edit:
To be clearer, my question is why do photons travel at all. Why do they have a ...
1
vote
1answer
42 views
Can a combination of two or more x-ray type beams be made to burn tumours at their intersecting focal points inside a body?
A single x-ray or similar type beam can pass through a human body with little or no damage. Has anyone ever tried to use a second beam that is phased to have no harmful reactions with the tissue ...
0
votes
1answer
153 views
The electron jumps and lets loose photons
Where is the source of the photon.
If the photon propagates from within the electrons transit does this point to some sort of field?
Does the energy come from a boundary being broken in laymens ...
3
votes
4answers
1k 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
0answers
126 views
What is the attenuation spectrum of radio waves in pure water?
Here is a plot of microwave attenuation in atmosphere:
(source)
I'm looking for a similar plot, but for pure water, and a frequency range covering at least 100 MHz to 2 GHz, hopefully more.
2
votes
2answers
100 views
Could you make a bar of metal glow by forcing the charge density on the surface to oscillate?
Since light is just a changing electromagnetic wave through space, could you create light by changing a charge density at a certain frequency?
0
votes
1answer
35 views
Radiation from farther galaxies
I've read many facts from NASA's webpage.. Sometimes they tell, (for example) "NASA's Chandra X-Ray Observatory discovered this ultra-luminous X-Ray source (about 15 million LY) which shows an ...
2
votes
1answer
237 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 ...
0
votes
2answers
181 views
Counting electromagnetic modes in a rectangular cavity and boundary conditions
The electric field in a cubical cavity of side length $L$ with perfectly conducting walls is
$E_x = E_1 \cos(n_1 x \pi/L) \sin(n_2 y \pi/L) \sin(n_3 z \pi/L) \sin(\omega t)$
$E_y = E_2 \sin(n_1 x ...
1
vote
2answers
364 views
Parallel-plate capacitor
I'm trying to grasp parallel-plate capacitors in a class of electromagnetic field theory. My book leaves out a lot and I couldn't figure it out from what I found on Google.
The book's procedure is ...
13
votes
3answers
516 views
Can light exists 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 ...
2
votes
2answers
110 views
What is the history behind the factors of 3 in the classification of electromagnetic radiation?
What is the history behind the factors of 3 in the classification of electromagnetic radiation?
See e.g. http://en.wikipedia.org/wiki/Radio_spectrum#By_frequency
Is this (just) inherited from the ...
4
votes
2answers
150 views
Is it possible to split a single light beam into two beams of opposite circular polarization?
A properly oriented calcite crystal will separate an unpolarized beam into two beams, one vertically polarized and one horizontally polarized. Other polarizers pass just one polarization and absorb ...
3
votes
2answers
68 views
limits on a gauss box of light
Consider a wall defined by $w(x,y,z) = \Theta(x-L)$ which is nonzero in the infinite semi-space of $x \ge L$, as well as a coherent planar standing EM wave travelling in the $z$ plane given by its ...
