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)

1
vote
1answer
31 views

How are the frequency and wavelength of electromagnetic waves affected within an event horizon?

I apologize if this has been asked previously or if my thinking is way off base, but I am inexperienced with relativity (and this is my first question on the site). I am wondering; as one (not ...
-1
votes
0answers
24 views

Faraday Cage for radiations from Uranium

Is it possible to build Faraday Cage like structure for Gamma Radiations or Beta radiations, so that a person inside that cage or sphere so that inside person remain protected from nuclear explosion. ...
0
votes
0answers
33 views

Electron in a Magnetic Field: Force parallel to velocity?

According to the four-force given in this question, Force is parallel to velocity. But the Lorentz Force is perpendicular to velocity in a constant magnetic field. Is this a contradiction? [a ...
5
votes
3answers
81 views

Do hot metals radiate? (Thermography)

I was looking into thermography which talks about emissivities of metals and other materials. Polished metals which have low emissivity appear to be colder in thermal imaging cameras even if they are ...
13
votes
2answers
2k views

How do you make a spherical radio wave?

A vertical rod, a usual dipole, produces radio waves in the horizontal plane, mostly in two opposite directions: If that is possible, how do you produce a spherical EM radiation? should the ...
3
votes
1answer
171 views

Hidden momentum

I'm trying to learn about hidden momentum. After reading what I could find with a google search, I understand that it is equal to the momentum carried by radiation, calculated with the Poynting ...
1
vote
3answers
73 views

Why don't E&M fields change orientation after hitting a surface?

In essentially every derivation of the Fresnel equations, the general problem of radiation hitting a surface at a certain angle is broken into two parts (out of which we hope the solution any general ...
1
vote
1answer
63 views

How does Compton scattering demonstrate particle over wave behavior?

Why is Compton scattering thought to demonstrate light's behavior as a particle over that as a wave. I'm interested in the thoughts at the time of Compton, but also how it contradicts current theory ...
1
vote
2answers
167 views

How can the thrust due to radiation pressure be amplified in photonic laser thruster?

The thrust is amplified due to repeated bouncing of photons between two mirrors as shown in the diagram in this: Why does repeated bouncing of photons produce amplified thrust when the answer in ...
64
votes
8answers
76k views

Why does a remote car key work when held to your head/body?

I was trying to unlock my car with a keyfob, but I was out of range. A friend of mine said that I have to hold the transmitter next to my head. It worked, so I tried the following later that day: ...
1
vote
2answers
32 views

What is the player's role in the functioning of a theremin?

I recently see a video on how the theremin works, and wasn't satisfied with the answer. I watched around, but they all seem to give the same explanation. A diagram as below is given, and it is ...
3
votes
2answers
2k views

Why is the atmosphere transparent in the visible spectrum?

One of the great 'coincidences' in physics is that the Sun happens to shine most brightly at exactly the wavelengths our eyes can see; it's an easy explanation that our eyes evolved to make the most ...
23
votes
1answer
845 views

How can my window not scramble the image of my yard?

How can an image pass through a window if the atoms in the glass randomly emit photons in any direction? I've read that glass is transparent because the atoms don't readily adsorb visible light, so it ...
2
votes
1answer
34 views

Wave Velocity vs. Phase Velocity

I am trying to understand the difference between 'wave velocity' and 'phase velocity'. I know that generally they are equal, but when is that not the case? I, of course, tried to google it, and ...
1
vote
1answer
50 views

A single light-wave's ability to divide into two halves?

We know from the double-slit experiment conducted "one photon at-a-time" that a light-wave, upon encountering two closely-spaced apertures, is able to split into two halves and travel through both. ...
-4
votes
1answer
51 views

How to shield myself from the LTE radiation coming from my phone while working on my Laptop? [closed]

I am connecting to the internet with the tethering option on my phone. I wonder if there is a way to shield myself from the LTE radiation (Long-Term Evolution, commonly marketed as 4G) as I am exposed ...
0
votes
2answers
343 views

Absorbance by using Poynting vector

How should I compute the amount of energy of an EM wave absorbed by a material? Can I just use the divergence of the Poynting vector?
0
votes
1answer
27 views

Frequency dependence of electromagnetic reflection

I was surprised to see that the Fresnel equations for reflection depends on refractive index and angle of incidence, but they do not depend on frequency. Why is this case? Are they restricted to ...
0
votes
5answers
134 views

How to increase the frequency of light

If we want to increase the energy of the emitted photoelectrons (in P.E) then we should increase the energy of the photons which are related to the frequency of the light, so how is the frequency of ...
27
votes
3answers
4k views

Why do X-rays go through things?

I always heard that the smaller the wavelength, the more interactions take place. The sky is blue because the blue light scatters. So why is this not true for X-rays, which go through objects so ...
-1
votes
2answers
43 views

What exactly are EM waves? [closed]

What exactly are EM waves? Wave is just a graph of the intensity of energy at the given point in space right? At a particular point in space, we detect that energy is going up ad then down with each ...
1
vote
0answers
92 views

How to derive equation for time it takes photons to diffuse through the Sun

I am wanting to use the Rosseland radiative heat flux equation to find the time it takes for photons to diffuse through the sun. The answer I am wanting to derive is: $$\tau_D~\frac{\rho \bar C_p ...
0
votes
1answer
53 views

Is fire more harmful than a phone?

I have read somewhere that the higher the frequency of electromagnetic radiation, the higher the damage it causes to your body, and visible light has a very high frequency in comparison to microwave ...
0
votes
0answers
13 views

Why does a 2-sided propagating EM wave become 1-sided if B is made proportional to E?

If you simulate the propagation of an electromagnetic wave in 1D free space (no charges or currents) with initial conditions of $E\neq0$ and $B=0$, and you look at a movie of $E$ vs time, then after ...
0
votes
0answers
29 views

Problem with understanding boundary conditions in electromagnetism

In some books on electrodynamics they stress that electric current won't radiate if it is placed on a perfect electrical conductor (PEC), citing image theory: exactly opposite current will appear and ...
2
votes
2answers
175 views

Momentum around an accelerated electron

Assume that an electron is accelerated along the +x-axis. The electron will radiate electromagnetic energy and momentum in every direction. But it seems to me that the EM momentum it radiates in ...
6
votes
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?
3
votes
1answer
42 views

How much ionizing (carcinogenic) radiation is one exposed to on a commercial flight, what are the sources, and how could exposure be minimized? [closed]

I don't know if this is the best place to ask this question, but I figure a physics-based answer would be the most satisfying. I'd be happy to be convinced I'm being paranoid about protecting an ...
0
votes
0answers
43 views

Gradient of Greens function

This question is about Jackson's equation (10.75) and (10.77) I don't know the step in between these two equations.I'm not sure what our unit vector $n'$ will be here and how can we take gradient of ...
0
votes
0answers
17 views

Why the angular distribution of the X-rays from Roentgen tube is not along the decelaration of electrons? [duplicate]

As I understand the X-ray generation from Roentgen tube, is a result from the bremsstralung (and also characteristic lines): from decelerating electrons in the presence of the potential of heavy ...
1
vote
0answers
43 views

Can 2 photons make up the same colour as another photon?

So, my question deals with the excited electron shown above. (1st diagram) This electron can return to its ground state by either of two ways. One of the ways involves the emission of 2 photons. ...
1
vote
1answer
21 views

Mie theory: Interpretation in terms of intensity

I'm trying to understand Mie theory. For this I'm reading the book "Absorption and Scattering of Light by Small Particles" by Bohren and Huffman. The derivation of the formulas is fine, but I'm stuck ...
0
votes
0answers
27 views

Detecting position of electrons [duplicate]

To detect particles like electrons, why would the accuracy of the position determined be affected by the wavelength of EM wave used?
2
votes
2answers
3k views

Young's Double Slit experiment question

Q-A beam of light consisting of two wavelenghts 600 nm and 450 nm is used to obtain interference in Young's Double Slit experiment (YDSE). Find the least distance from the central maximum where the ...
0
votes
2answers
47 views

Definition of a ray?

The typical definition of a ray and the one that I was initially taught was that a ray was a line perpendicular to the wave front. However, when reading up on birefringence it seems as though there ...
0
votes
1answer
26 views

Reflection coefficient of surface with sources

While solving the maxwell equation for surface where both surface charge and current density are present to calculate its reflection coefficient, i.e. $$\nabla \times E=-\frac{\partial}{\partial ...
2
votes
1answer
149 views

polarization of a transverse wave travelling in ionosphere with polarization direction perpendicular to earths magnetic field

Assume a transverse electromagnetic wave entering ionosphere such that its Electric field of wave is perpendicular to earths magnetic field. Now, i read that as it will enter plasma, the wave will ...
3
votes
1answer
41 views

Relation between the electromagnetic wave and quantum wavefunction

I have been thinking about this for a while. I think I misunderstood something about the basics of quantum waves. Let's look at light diffracted in conditions similar to the double slit experiment. ...
0
votes
1answer
54 views

Interference of light waves question

We were recently asked to solve a question in class which goes as follows: In a modified Young's double slit experiment, a monochromatic uniform and parallel light beam of wavelength $6000$ ...
1
vote
2answers
69 views

Are wave fronts in double-slit experiments moving forward? [closed]

I ask a question about "What is a wavefront?" which follows the question "What makes the radiation behind a slit coherent". For the wavefront it was answered, that "In electromagnetics ...(that are) ...
0
votes
0answers
22 views

Intensity of interfering light waves

I had a conceptual question above light wave interference. Suppose that two light beams, each of an irradiance $I$ interfering on an area $A$ of a screen, such that all of the light from each beam ...
2
votes
1answer
67 views

What causes electromagnetic waves to propagate in free space?

In free space, $\rho=0$ and $J=0$, so there are no electromagnetic sources/sinks. Maxwell's equations thus reduce to: $\nabla\cdot E = 0$ $\nabla\cdot B = 0$ $\nabla\times E = -\frac{\partial ...
0
votes
0answers
19 views

What does relative permitivity of medium mean and what does it depend on?

Does relative permitivity have someting to do with the polarization of medium , like for example how in inside the capacitor magnitude of electric field would be less due to a smaller opposing field ...
0
votes
0answers
16 views

the inner self-inductance of coaxial cable using integration

I'm trying to calculate the inner inductance of a coaxial cable using integration knowing that the answer is : $L=μl/8π$ i get the same answer when i take a cylindrical shell of thickness $dr$ but the ...
0
votes
1answer
36 views

Photoelectric effect on charged plate

As far as I know, to observe the photoelectric effect, one has to expose a metal surface to high-energy radiation. But what happens if the surface has a surplus of electrons? What is the energy needed ...
1
vote
1answer
73 views

Why is glass green?

When I look at a glass block at an angle the edges appear green, but when I look at the edge sideways, so that is directly in front of my eyes it appears transparent. Why?
8
votes
4answers
144 views

Why do the edges of glass blocks create a shadow?

I have always observed that the shadow of glass blocks becomes darker as the glass is moved away from the surface where the shadow falls. And I know this is because refracted light rays from the glass ...
-2
votes
2answers
68 views

Speed of RF waves and IR waves is same as 3 * 10 ^8 m/s?

In space,if we want to measure the speed of RF waves and IR waves it will be roughly 3 * 10^8 m/s ( SPEED OF RF WAVES = SPEED OF IR WAVES = 3* 10^8 M/S ) is this correct ? The different in the ...
15
votes
1answer
914 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 ...
0
votes
1answer
41 views

Speed of light in vacuum in special relativity

In special relativity, the speed of visible light is defined as a constant. But visible light is only a small part of the electromagnetism field. So why?