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

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31
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8k 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 ...
7
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2answers
3k 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 ...
0
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0answers
123 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 ...
18
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2answers
22k views

How and 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 ...
9
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2answers
1k 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 (...
9
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4answers
5k 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 ...
37
votes
5answers
6k views

Why doesn't light kill me?

Why does each individual photon have such a low amount of energy? I am hit by photons all day and I find it amazing that I am not vaporized. Am I simply too physically big for the photons to harm me ...
1
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0answers
30 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
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1answer
290 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 ...
2
votes
4answers
10k 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 ...
2
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2answers
135 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 ...
2
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1answer
126 views

Trying to understand EM wave and photon

When electrical fields and magnetic fields couple together, it forms electromagnetic waves. And we can "quantized" it and see each "package" of it as photon. So can electrical fields and magnetic ...
5
votes
2answers
254 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 ...
3
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2answers
1k 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
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0answers
387 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 ...
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 ...
4
votes
4answers
995 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 ...
4
votes
2answers
1k 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
276 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 ...
2
votes
1answer
506 views

Uncertainty-principle and the Maxwell formalism of electromagnetic waves

An electromagnetic wave (like a propagating photon) is known to carry it's electric and magnetic field-vectors perpendicular and each depending on the differential change of the other thus "creating" ...
0
votes
1answer
75 views

Phasor representation of voltage in frequency domain

In a text on application of electromagnetism in transmission line, there introduces a phasor for the voltage (in frequency domain) $$\tilde{V}(x) = V^+e^{-i\beta x} + V^-e^{i\beta x.}$$ Here $V^+$ ...
3
votes
1answer
7k 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 ...
3
votes
1answer
1k views

What properties make a good barrier for microwave (oven) radiation?

Suppose I have plenty of food I want to heat (which will provide load) in the microwave, and one item I don't want to heat. What properties would make a material a a good shield, to reduce or prevent ...
3
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2answers
280 views

What materials focus EM radiation in the 2.4GHz range

If glass and similar materials refract visible light effectively, what materials would be best for focusing lower frequencies of EM radiation, if any? If not, what other methods exist for focusing ...
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0answers
126 views

Longitudinal EMAG wave?

I'm reading about optical waveguide analysis, and often come across the terms "transverse electric mode" vs. "transverse magnetic mode". As I unerstand, it means that the electric/magnetic field has ...
0
votes
1answer
196 views

Fundamentals of electrostatics

Suppose I have a Gold Leaf Electroscope and the leaves are observed to diverge by a certain amount. Now if I send a beam of X-rays and allow it to fall upon the electroscope for a very short period of ...
0
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3answers
833 views

Why doesn't a stationary electron lose energy by radiating electric field (as per coulomb's law)?

If an electron in a universe constantly generates an electric field why does it not get annihilated ? I am confused because I read that an accelerating charge radiates and loses energy. So, why won't ...
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1answer
149 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 ...
4
votes
1answer
8k views

What is the difference between Radiation and Electromagnetic Radiation

Are the two equivalent or is Electromagnetic Radiation a subset of Radiation. I am further confused by the fact that electromagnetic radiation includes both ionizing and non ionizing types of ...
0
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0answers
107 views

Curie's principle in electromagnetic field theory

I am looking for some explanation and if possible also some references about the applications of Curie's principle in electromagnetic field Theory, precisely in the computation of magnetic (resp. ...
0
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2answers
677 views

Bremsstrahlung: why is electron slowed/stopped by the positive nucleus?

I can't understand why the electron is slowed/stopped by the nucleus. The electron is a negative charge and the nucleus is positive... they should attract each other...
2
votes
0answers
232 views

Fourier Transform of ribbon's beam Electric Field

I have a monochromatic ribbon beam with $E(x)e^{i(kz-\omega t)}$ being the electric field's amplitude. I want to show that the lowest order approximation in terms of plane waves is $\mathbf{E}(x,z,t)=...
1
vote
1answer
1k views

Power radiated by the Sun at different locations [closed]

I am wondering can someone help to solve second part which extends first part; The power radiated by the Sun is ${3.9*10^{26}}_{watt}$. The earth orbits the sun in a nearly circular orbit of radius $...
3
votes
1answer
182 views

Can you “fold” EM or light waves? (i.e) long wave that is reflected by mirror in fragments - like in the game “Snake”

So, I was reading about the Casimir effect. Two mirrors facing each other attract to each other in a vacuum. The reason is due to pressure exerted on those mirrors from the multitude of EM waves (like ...
5
votes
2answers
8k views

What are coherent and incoherent radiation?

What are coherent and incoherent radiation? I am a mathematician who is self-learning physics. In reading Jackson's electrodynamics and other books, I often hear that radiation is incoherent or ...
2
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3answers
826 views

Producing electricity from all wavelengths of electromagnetic spectrum

Is it possible to produce electricity from all wavelengths of electromagnetic spectrum beside visible light ?Like using gamma rays or x-rays .
2
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0answers
326 views

Analytical solution of two level system driving by a sinusoidal potential beyond rotating wave approximation

A quantum mechanical two-level system driving by a constant sinusoidal external potential is very useful in varies areas of physics. Although the wildly used rotating-wave approximation(RWA) is very ...
3
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3answers
3k views

Is there any example where electric and magnetic fields are not perpendicular?

Perpendicular electric and magnetic field creates light or other electromagnetic waves. Is it a necessary property to have a perpendicular fields? If not what would happen when the fields are not ...
2
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3answers
4k views

If photons can be absorbed by electrons, wouldn't that mean light has a charge? [duplicate]

I am a biochemistry and molecular biology major. If photons can be absorbed by electrons, wouldn't that mean light has a charge? Electrons only attract positive charges. Isn't it?
1
vote
1answer
110 views

What happens to the $2\pi$ factor when calculating Raman-shifts in units of wavenumbers?

So from the classical theory, you find a formula for a dipole in a planar electromagnetic wave, where there will be two cosine terms with a frequency (actually angular velocity in $[rad/s]$, as the ...
2
votes
1answer
535 views

How to calculate beam spread of a non-point light source via an aspheric lens

I need to determine the angle, or rate of divergence of light from a single aspheric lens when I place a non-point light source (e.g. LED array) at a given distance from the lens which is less than ...
0
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0answers
65 views

Time reversed laser

Recently, I read an article on time reversed laser. I don't know why they call it a time reversed. I have a doubt that why they use two laser in the device. And what is an anti-laser? The device ...
0
votes
2answers
715 views

New infrared laser weapon made by the USA - How does it work? [closed]

I have seen this post: New infrared laser weapon, the Laser Weapons System, could shoot down drones or disable ships: US Navy You can watch the video as well. that exhibits a laser weapon which can ...
1
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1answer
396 views

Why do CD's shatter in a microwave?

Why have I heard that eggs and CD's and DVD's explode when microwaved?
4
votes
4answers
397 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
1answer
759 views

Photon Absorption and Emission: Conductors v. Semiconductors

I'm having a hard time understanding how photon absorption and emission in metals (conductors) compares to semiconductors. Obviously, in SCs, absorbed photons lead to electron-hole pairs and emitted ...
1
vote
1answer
260 views

william herschel discovering infrared problem

when william herschel conducted the experiment of separating white light with a prism and measuring the different colors, he put a thermometer past the red color as a control finding it to pick up the ...
1
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5answers
3k views

The rule breaker, emissivity + reflectivity = 1

If emissivity and reflectivity are inversely proportionate, why does glass have a high emissivity of around 0.95-0.97 as well as being very reflective for IR Radiation? normally it works but not with ...
0
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3answers
605 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 ...
-1
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1answer
1k views

What is longitudinal relaxation time and transverse relaxation time? [closed]

How do we define the longitudinal relaxation time and transverse relaxation time?