# Tagged Questions

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

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4answers
2k 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 ...
0answers
19 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 ...
1answer
22 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 ...
1answer
68 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 ...
1answer
40 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 ...
2answers
72 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 ...
2answers
35 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?
0answers
39 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 ...
1answer
45 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 ...
1answer
66 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 ...
2answers
78 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?
1answer
52 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 ...
1answer
70 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" ...
1answer
27 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 $V^+$ ...
1answer
46 views

### Where is the amplitude of electromagnetic waves in the equation of energy of e/m waves?

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 ...
1answer
68 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 ...
2answers
51 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 ...
0answers
43 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 ...
1answer
24 views

### Charge gained due to photoelectric effect [closed]

Here I think, one beam will knock out just one electron. So, I am not able to even understand what the question says. Please someone give a hint as to what the question asks... As source of the ...
0answers
28 views

### Why is Electromagnetic Spectrum Bounded? [closed]

The Electromagnetic Waves having frequencies between $10^{4}Hz$ and $10^{20}Hz$, is called as an electromagnetic spectrum. Why these limits? What is the reason for spectrum to have boundaries? We can ...
0answers
34 views

### Difficulty in obtaining the Lorentzian lineshape for natural broadening [migrated]

Not sure if this maybe belongs more in the maths section, but since it comes from a physics problem i'll post here. when calculating the natural broadening lineshape for a laser we have to take the ...
1answer
49 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 ...
3answers
83 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 ...
1answer
45 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 ...
1answer
85 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 ...
0answers
54 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. ...
2answers
63 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...
0answers
46 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 ...
1answer
71 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 ...
1answer
76 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 ...
3answers
75 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 .
0answers
38 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 ...
0answers
132 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 ...
3answers
120 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?
1answer
41 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 ...
0answers
36 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 ...
2answers
186 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 ...
1answer
66 views

### Why do CD's shatter in a microwave?

Why have I heard that eggs and CD's and DVD's explode when microwaved?
4answers
180 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 ...
1answer
138 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 ...
1answer
30 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 ...
3answers
96 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 ...
2answers
61 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 ...
1answer
64 views

### What is longitudinal relaxation time and transverse relaxation time？

How do we define the longitudinal relaxation time and transverse relaxation time?
0answers
233 views

### Do EM waves transmit spin polarization?

Suppose you have a normal dipole antennae (transmitter and receiver) . Spin polarized current (as opposed to normal current) is sent into the transmitter, it emits an EM wave and the Receiver receives ...
2answers
189 views

### How do you calculate power at the focal point of a mirror?

I'm a Mechanical Engineering student and I'm working on my senior project, so I need help. My project is about designing a solar dish having a diameter of 1.5 meters and a focal length of 60cm. so at ...
2answers
158 views

### A charged sphere with pulsing radius

Radius increases and decreases periodically (as a pulse).And so does the charges on the surface of sphere. I can't get what is gonna happen.the EM waves are produced perpendicularly to motion of ...
2answers
177 views

### How photons represent colors that you see?

Right now, my understanding is that, a mixture of photons of many different frequencies is perceived as white by your eye. While no photons at all, is perceived as black. And photons with the blue ...
6answers
597 views

### What are the various physical mechanisms for energy transfer to the photon during blackbody emission?

By conservation of energy, the solid is left in a lower energy state following emission of a photon. Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium ...
1answer
84 views

### The length of an antenna is twice the amplitude of the wave

I have seen it remarked in some problem sets that if you have an electromagnetic wave traveling in the $x$-direction with it's $y$-coordinate given as $y(x,t)=y_0\sin (\omega t +kx)$ and you want a ...
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