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

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121 views

Energy conservation in plane wave

In plane wave the H and E are in phase. So the pointing vector disappears regularly every pi. How is energy conservation validated ? Is it through the uncertainty of energy and time ?
3
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1answer
114 views

electromagnetic interference

If the atmosphere is filled with electromagnetic waves all oscillating at different wavelengths and speeds how is it that they don’t all interfere with each other? For example turning on your light ...
3
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1answer
1k views

Decay of metastable state: spontaneous vs. stimulated emission.

I have a question about the upper laser level (the metastable level) in a 3-level laser system. I will call the ground level of the 3-level laser system by "g" and the metastable level by "m". The ...
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3answers
6k views

2 ways to generate electromagnetic wave

According to Maxwell's equations, accelerating charges emit electromagnetic radiation. According to Quantum physics, heating causes electromagnetic radiation too. These 2 radiations, are they ...
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5answers
863 views

Radio antenna producing waves in the visible spectrum

If a radio could produce waves in the visible light spectrum, what would the result be? This is a thought experiment that I've pondered for a few years now. I realize there are a few/many real-world ...
114
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1answer
48k views

Why does NASA use gold foil on equipment and gold-coated visors?

I've read several websites about equipment covered with gold foil and astronaut helmet visors are coated with gold. However, their explanations are devoid of almost all physics content. Can someone ...
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2answers
425 views

Is compton scattering only effective by x rayphotons and gamma ray photons

Can Compton scattering work with any other forms types of photons, and why was the the Compton Scattering experiment only done with x ray photons?
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0answers
493 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 ...
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1answer
113 views

What is the intensity of this light?

I am struggling with a derivation that calculates the cross sections for Mie scattering and since the incident light is considered to be a x-polarized plane wave I thought that we would have $$I_i = ...
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3answers
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If photons carry 1 spin unit, why does visible light seem to have no angular momentum?

Spin 1 silver atoms have a definite spin axis, e.g. up or down along an axis labeled X. This in turn means that they carry angular momentum in an overt, visible fashion. However, spin 1 photons do ...
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1answer
160 views

'Push' in a rigid rod travel at speed of sound or speed of light [duplicate]

Two person, $A$ and $B$, each holding one end of a long solid rod. Now person $A$ pushes the rod on one end. Question: Is it correct that the information that the rod has been pushed will travel ...
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4answers
612 views

Is the electromagnetic spectrum discrete?

I'm just starting to learn physics and I have a question (that is probably stupid.) I learned that energy levels that the bound electron can have are discrete. I also learned that when an electron ...
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1answer
272 views

Is there a way to increase photon energy by decreasing its wavelength?

Can I decrease a photon's wavelength by a medium or a vacuum? Are there other ways of decreasing the wavelength?
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2answers
292 views

What type of electromagnetic radiation strikes the Earth's surface the most?

If you can could you lists the types of light from the greatest amount to the least amount (Ex: Visible, Infrared, Violet).
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2answers
56 views

Where the extra power comes from?

Suppose we have two radio waveforms each has amplitude of 1, then the total power is 2. Suppose these two waveforms add up some where constructively, then the amplitude become 2, and the total power ...
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2answers
133 views

Does $E$ cause $B$ or does $B$ cause $E$ in Maxwell's equations?

From the Maxwell's equations we get $$\frac{\partial E}{\partial x} = -\frac{\partial B}{\partial t}$$ and $$\frac{\partial B}{\partial x} = -\mu_0\epsilon_0\frac{\partial E}{\partial t}$$ ...
4
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2answers
129 views

Applicability of the concept of voltage in electrodynamic circuits

In electrostatics, we have $$\nabla \times \vec{E} = 0$$. Hence, we can define a scalar potential $V$, where $$\vec{E} = -\nabla V$$. We know from Faraday's law that $$\nabla \times \vec{E} = ...
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2answers
599 views

The Quantization of Photon Energies [duplicate]

Despite Planck's constant being in $E=hf$, it would appear to me that energy is still not discrete, as frequency can be an fraction of a Hertz that one wants. How does this imply that electromagnetic ...
3
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2answers
140 views

Colors of light

White light is always said to contain all the different wavelengths of light. Why, then, can we 'make' new colors simply by adding wavelengths? Is it just a matter of our perception, that, when two ...
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2answers
911 views

Gravitational slingshot of light using a black hole/massive object

Wikipedia has this page on gravity assists using planets. In some cases this effect was used to accelerate the spacecraft to a higher velocity. This diagram shows this in a very oversimplified manner. ...
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0answers
80 views

Mie Scattering for spheres with constant dipole moment

I was wondering whether there exists a theory that describes Mie Scattering for spheres that have a constant dipole moment. Since there are theories that describe Mie scattering in the case of a ...
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1answer
233 views

Retarded potential in gravitational field?

Is there a retarded potential concept in gravitational field similar to electromagnetic radiation?
5
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1answer
551 views

Could an oscillator at a high enough frequency produce light instead of radio waves?

Considering that light is in the 400-800 THz range, if you had an electrical oscillator that ran at that frequency connected to an aerial of some sort, would the antenna emit visible light, in the ...
4
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1answer
161 views

Light entering in a 0° angle, is there any reflection?

Is there any reflection of light that enters a new medium at a 0° angle, if the electric field is such, that it is completely in the plane of the double layer?
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1answer
189 views

Reflection, transmission, absorption…how to calculate them?

I was wondering whether there is an equation that enables me to calculate the reflection, transmission, absorption and polarization, when the electric field everywhere is given? Consider this: You ...
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1answer
60 views

What are the properties of the Electromagnetic wave $E=E_0e^{-i\omega t}$

My question is, whether this definition $E=E_0e^{-i\omega t}$ includes that it is a plane wave, since I am confused by the fact that we do not have any dependence on the position. So about what kind ...
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1answer
589 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 ...
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4answers
738 views

Can a wave be two dimensional?

I am having a hard time picturing waves, the image that comes to mind is a bobbing device submerged in still water which generates pulses in all directions (similarly in air). Then how can a wave be ...
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1answer
449 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 ...
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2answers
434 views

Electromagnetic Momentum

My book says : The fact that electromagnetic radiation of energy carried momentum was known from classical theory and from the experiments of Nichols and Hull in 1903. This relation is also consistent ...
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2answers
151 views

Interaction of coherent X-rays with matter

If we could irradiate a metal or a plasma with a coherent beam of hard X-rays, would the main effect be an ordered oscillation of the electrons like with a classical EM wave, or "compton-style" ...
2
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1answer
68 views

Radiation interactions: how is the transition from the “electric” regimen to “particle-like” regimen?

When we study the interaction of the electromagnetic radiation with free electrons we can find two different approaches in the literature: for low frequency (RF, light...) a classical view is used and ...
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3answers
962 views

Why does a dielectric have a frequency dependent resistivity?

This question has come about because of my discussion with Steve B in the link below. Related: Why is glass much more transparent than water? For conductors, I can clearly see how resistivity ...
3
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1answer
124 views

Does magnetism affect corrosion?

Supposing there is an iron nail that is left to rust, if we compare the time it takes to rust with that of a magnetized iron nail, will there be any difference in the time of corrosion (assuming other ...
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3answers
235 views

Can visible light be emitted from a non-thermal source?

I was reading about thermal and non-thermal radiation and I was wondering if visible light can be emitted from a non-thermal source?
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2answers
802 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 ...
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0answers
149 views

Charge above a conductor; effects due to Lorentz force law for moving charges

Currently working through a practice preliminary examination problem. I have your standard charge situated a distance d from a infinite conductor(lets say in the $\hat{z}$ direction and neglecting ...
3
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1answer
91 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 ...
10
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1answer
252 views

Why aren't superconductors shiny? [duplicate]

Superconductors are really good at conducting electricity. Should they not reflect light very well too?
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3answers
306 views

Can I call additional conditions on potentials a Gauge choice?

Let's say I have an electromagnetics problem in a spatially varying medium. After I impose Maxwell's equations, the Lorenz gauge choice, boundary conditions, and the Sommerfeld radiation condition, I ...
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4answers
400 views

Why is laser light a cone?

What about the production of laser light disallows it to be perfectly straight as opposed to a cone? I feel like it should be a plane wave, not a very tight cone.
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4answers
4k views

Does a constantly accelerating charged particle emit em radiation or not?

The Abraham-Lorentz force gives the recoil force, $\mathbf{F_{rad}}$, back on a charged particle $q$ when it emits electromagnetic radiation. It is given by: $$\mathbf{F_{rad}} = \frac{q^2}{6\pi ...
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3answers
221 views

How “things” radiate electromagnetic radiation? [closed]

How things radiate electromagnetic radiation? I don't ask why they radiate (higher temperature than 0K) but how they radiate this electromagnetic waves?
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338 views

An Electromagnetic Paradox?

The above diagram represents an isolated system with two masses $M$, at position $X$, and $m$, at position $x$, connected together by an extended spring. Each mass is connected by rigid rods to ...
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1answer
270 views

home made atom destruction unit [closed]

Today we learnt at school that atoms can be destructed. I believe Physics is a great science to do experiment and I would like to try it at home. Could you tell me what I need to do it? and is it ...
21
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1answer
582 views

How do we know that these radio bursts are from billions of light-years away?

NASA just announced that they detected the first radio bursts from outside of our galaxy. Astronomers, including a team member from NASA's Jet Propulsion Laboratory in Pasadena, Calif., have ...
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1answer
611 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, ...
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3answers
1k views

Why electrons can't radiate in their atoms' orbits?

It's an old-new question (I found only one similar question with unsatisfactory (for me) answer: Where did Schrödinger solve the radiating problem of Bohr's model?) It's strange for me how all books ...
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3answers
939 views

Are Electromagnetic Waves The Only Means of Transmitting Information?

We've been using EMF to transmit energy (information) for over a century. I was wondering is there any other way to send a message on long distances, even faster than EMF waves can travel? For example ...
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1answer
309 views

How do individual photons make up an EM wave?

I'm trying to understand the connection between the wave model and the particle model for light. It's understood that the energy of a photon is given by E=hf, but from my understanding of fourier ...