Propagating solutions to Maxwell’s equations in classical electromagnetism and real photons in quantum electrodynamics. A superset of thermal-radiation.
2
votes
1answer
11 views
polarization of the lower mode gaussian beam
In most introductory analysis of Gaussian beam optics, Helmoltz scalar optics is assumed. Hence polarisation is ignored. But I'm not clear what are the possible orientations for the lower transverse ...
1
vote
1answer
175 views
Two photons transition
if an atom in its ground state is coupled to an electromagnetic field it can absorb a photon if the EM field contains one with the right frequency. These transitions depends on $⟨f|H_i|i⟩$ (from ...
25
votes
9answers
14k views
If photons have no mass, how can they have momentum?
As an explanation of why a large gravitational field (such as a black hole) can bend light, I have heard that light has momentum. This is given as a solution to the problem of only massive objects ...
5
votes
1answer
66 views
Photons: Collection of Wave Packets that produce a plane wave
Is it possible mathematically for photons, which behave as individual Gaussian wave packets, to combine in such a way that the approximate result is a plane wave at one particular frequency (i.e., the ...
0
votes
0answers
12 views
What is the relationship between UV wavelength and penetration depth into human skin? [migrated]
Some background - Some recent research has strongly suggested that UVA penetration into the skin is far more dangerous than UVB, a very good example is this paper by Agar et al. (2004).
My query is, ...
3
votes
2answers
43 views
Black body radiation
I have a few questions related to the emission of electromagnetic radiation by black bodies. Consider the following image:
On the above image I have drown the rays of light that are emmited by ...
3
votes
3answers
62 views
MRI's and Electromagnetic Radiation
If the waves in an MRI can go through our body, why is it that light with its magnetic fields gets stopped at our skin?
2
votes
1answer
68 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 ...
8
votes
2answers
2k 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
...
5
votes
1answer
64 views
Astronomical-wavelength radio (AWR) transmissions between cosmic plasmas?
My son asked me if electromagnetic waves longer than radio exist. I told him that even though physics permits such waves, there are no antennas long enough to radiate or detect them.
However, on ...
-1
votes
0answers
37 views
Reference Request: Mantle Cloaking, Invisibility and Metascreen [closed]
Reference Request: Mantle Cloaking, invisibility and Metascreen.
I'm really interested in Mantle Cloaking but I've difficulties in finding some basic references in order to study foundamental ...
-2
votes
0answers
73 views
Velocity, Wave Equation, Differential Equations [closed]
Suppose you have a differential equation of the form:
$$
\frac{\partial^2 u}{\partial z^2} = C \frac{\partial^2 u}{\partial t^2} + D \frac{\partial u}{\partial t}$$
Is it possible to find the ...
1
vote
1answer
55 views
Simple Question: Speed of Electromagnetic Waves in a Medium
If the speed of an electromagnetic wave in a particular medium is such that $v = c$, the speed of light, does this mean that the permeability $\mu = \mu_0$, i.e. that of a vacuum and the index of ...
6
votes
1answer
95 views
How could we see microwave radiation with our eyes?
A few years ago I read a short little article about how big our eyes would have to be to observe microwaves (or any long-wave radiation for that matter). I don't remember enough about the article, or ...
14
votes
3answers
844 views
Amplitude of an electromagnetic wave containing a single photon
Given a light pulse in vacuum containing a single photon with an energy $E=h\nu$, what is the peak value of the electric / magnetic field?
1
vote
1answer
61 views
Does an accelerating proton also lose mass?
A proton accelerated with electric field gives off E.M. radiation and therefore should lose mass. Larmor's formula gives us a value for the power emitted (varies as acceleration squared). However, as ...
2
votes
1answer
98 views
Where is the amplitude of electromagnetic waves in the equation of energy of e/m waves? [duplicate]
Does the amplitude of the photon oscillations always stay constant and if it is not - what are the physical differences between the photon with higher amplitude in comparison to the one with the less ...
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
97 views
Special Theory of relativity on electromagnetic waves
Since time slows down and length contracts, when we travel almost at speed of light, if the speed of light (or EM waves) remains same and the wavelength of light remains same, do we measure the ...
2
votes
1answer
48 views
Why, in EXAFS spectrum, does the absorption coefficient monotonically decrease with increasing photon energy?
In atomic physics, it is common knowledge that following the absorption edge, where the photon energy equals the binding energy of a core electron, a monotonic decrease in the absorption coefficient ...
3
votes
1answer
39 views
Interaction of an electromagnetic wave with a two level system in the domain of quantum field theory
Suppose I shine an electromagnetic wave on a two-level system. I need to describe how the system evolves in context of quantum field theory i.e. using a quantized EM field in the problem. The first ...
0
votes
2answers
97 views
Are waves on water an example of gauge invariance?
So: Is the close similarity of small waves crossing water of varying depths ("depth potentials") an example of an approximate gauge invariance?
If so, do other "only the surface dynamics matter" ...
0
votes
1answer
54 views
How can we observe lights properties if it travels at the speed of light, or can we? [duplicate]
Special relativity says that anything moving (almost) at the speed of light will look like its internal clock has (almost) stopped from the perspective of a stationary observer. How do we see light as ...
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 ...
14
votes
3answers
293 views
Why do prisms work (why is refraction frequency dependent)?
It is well known that a prism can "split light" by separating different frequencies of light:
Many sources state that the reason this happens is that the index of refraction is different for ...
1
vote
1answer
58 views
Super High Frequency Electromagnetic Radiation - String Theory
I am a serious high school student with one year of physics class experience, so please point out if there are any flaws in my question or reasoning. Thanks!
Gamma ray radiation possesses a ...
4
votes
4answers
220 views
Are photons deterministic?
I propose the following scenario:
At $t=0$, a photon is emitted from a star. At $t=n$, said photon is received and interpreted by some detector.
My question is whether or not it is accurate to say ...
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 ...
5
votes
2answers
188 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 ...
30
votes
5answers
4k views
Why doesn't light kill me?
I was attending my philosophy class and in the middle of student presentations, I found myself mentally wondering off and thinking about light. After a few minutes of trying to piece together how the ...
1
vote
1answer
60 views
Electromagnetic field to cool a substance?
I saw somewhere that an electromagnetic field would cause a substance to let off thermal energy, ultimately resulting in the substance to cool really quickly.
If this is possible, does the strength ...
3
votes
1answer
235 views
Is there a limit to the visual information a photon can carry?
As photons bounce around and finally find their way into our eyes, are they continually relinquishing the information of the previous thing they "bounced off of"? Is this the reason why we receive a ...
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 ...
3
votes
2answers
475 views
Are Colors Emitted at Specific Temperatures?
There are quite a few nagging questions I have been having over the years, I do not require a full explanation, just some guidance in my assumptions and pointers if I am very wrong.
My basic ...
0
votes
0answers
25 views
UV light penetration into silicon
I'm in need of some information about UV (particularly UVA) light's ability to penetrate into silicon. Specifically, I am looking for a relationship between wavelength and penetration depth. Also, if ...
2
votes
2answers
101 views
How & Why does accelerating charges radiate electromagnetic radiation?
Lets consider it case by case:
Case 1: Charge particle is at rest. It has electric field around it. No problem. That is its property.
Case 2: Charge particle started moving (its accelerating). We ...
0
votes
0answers
39 views
Historical aspect of wave theory of light
Huygens thought light as a wave. Wave is a propagation of physical disturbance. We now know that light is electromagnetic field. Electric and magnetic field fluctuates here. What Huygens really ...
5
votes
2answers
94 views
If light rays obey to the wave equation, why can they be thought as straight lines?
I'm a newbie with physics but I'm wondering how a ray of light can essentially be represented. I have always known that a ray of light proceeds in a straight line until it encounters another object ...
2
votes
3answers
116 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 ...
-1
votes
0answers
44 views
Object $A$ : Object $B$ [closed]
Object $A$ has the ability to send information via some wavelength.
Object $B$ houses object $A$ and has the ability to detect when wavelengths are transmitted.
What is object $B$?
0
votes
0answers
21 views
Does quantum mechanics depend solely on electromagnetic waves? [duplicate]
I am beginning to learn quantum mechanics. Since determining the position of an object involves probing by electromagnetic waves and since i have read a simple derivation of Heisenberg's uncertainty ...
0
votes
1answer
30 views
Effectivness of a metallic wall against microwaves propagation
I would like to know how good or bad behave a metallic wall in stopping the propagation of an microwave signal.
To be practical, let's take the example of a GSM relay antenna. If I set up the ...
1
vote
1answer
83 views
How can we detect X-rays?
I know that X-rays can be detected by various ways, like ionizing of air particles.
Is there a way to detect X-rays,which are photons, by detecting ? Can something absorb the energy of the X-rays and ...
0
votes
1answer
46 views
Energy in Electromagnetic Waves
Looking at diagrams of Electromagnetic Waves, it would appear to me that at certain times the waves have zero amplitude, and consequently zero energy. Indeed, substituting in the sinusoidal terms into ...
3
votes
2answers
83 views
Is light's path a wave?
In a lot of textbooks I see a schematic of light drawn as a squiggly line. I have even heard that some things are too small to be seen because they are smaller than the wavelength of light (and ...
2
votes
0answers
87 views
Mathematical equivalence between Liénard-Wiechert potential and 4-potential in Rindler coordinates
I'm studying the problem of the radiation of an uniformly accelerated point charge:
$$x^{\mu}(\lambda)\to(g^{-1}\sinh g\lambda,0,0,g^{-1}\cosh g\lambda)$$
I found that when a point charge is moving ...
3
votes
1answer
316 views
How does the grid on the microwave oven window prevent microwave radiation from coming out?
If I look through the microwave window I can see through, which means visible radiation can get out. We know also that there is a mesh on the microwave window which prevents microwave from coming out.
...
2
votes
1answer
80 views
Difference between electromagnetic radiation (EMR) and Electromagnetic Field?
I'm a freshly graduated electrical engineer. One course that I really struggled with was Field Theory, because it was a lovely assortment of vector calculus and things that were explained to me well ...
3
votes
2answers
97 views
What happens to the energy not absorbed by a radio?
If a radio tunes to a specific frequency, where does the excess energy go? If one continues to hit the resonant frequency, shouldn't the wire begin to melt at some point from too much energy?
5
votes
1answer
57 views
Temperature of glowing materials
As I understand it, Stars emit visible light, OBAFGKMRNS, in the range of $10^3 - 10^4 K$.
Yet materials such as steel emit similar frequencies at much lower temps; red is around 800K.
Why the ...
