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

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105 views

If photons have mass then how can they travel at speed of light? [closed]

Anything that has mass must be slower than speed of light. If they are travelling at speed of light they must contain infinite energy which should be able to destroy everything, clearly thats not ...
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0answers
32 views

Confusion about radioactivity

The following question is from General Problems on Physics by I.E Irodov 6.220. Find the decay constant and the mean lifetime of $^{55}\operatorname{Co}$ radionuclide if its activity is known to ...
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2answers
109 views

Can wifi signal reception be improved by opening a door? [closed]

Use Case A wifi user is in a different room than the router. The computer is having a hard time connecting and receiving the wifi signal. Engineering Question Can the wifi signal from the router to ...
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0answers
80 views

Can TE and TM modes propagate together in a waveguide?

I recently came to understand the TE and TM modes. As it is defined that E=0 for transverse electric and vice-versa. I have a few basic questions in mind which I thought to ask in one thread only. Q....
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3answers
109 views

FWHM increase with energy (gamma spectra)

Below I have two plots from a gamma spectrum which I've been analyzing. The first plot is between a low energy range, the second between a significantly higher energy range. It is clear that the FWHMs ...
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2answers
110 views

How is frequency related to kinetic energy?

Does producing higher frequency waves require more energy than their low frequency counterparts with same amplitudes? For example, in electronics, would a 500 kHz wave require higher voltage to ...
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1answer
37 views

Why aren't EM waves directionless?

I've seen some descriptions of electromagnetic waves of late, almost comparing the wiggling an electron (or any charge) to the disturbing of a water surface, and as a result waves are formed that ...
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2answers
133 views

Why don't objects radiate off all of their heat energy?

Imagine a solid box in deep space. Solids are as far as I know constructed by positive nuclei in some sort of coherent structure, with electrons orbiting nearby too. Both the nuclei and the ...
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2answers
71 views

What is electromagnetic radiation exactly? [closed]

What exactly is electromagnetic radiation? Other than the maths involved I'm not able to understand it at an intuitive level, can somebody please explain what it is?
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13 views

How do i calculate the “attenuation effect” that of a perforated aluminum sheet?

I am conducting an experiment test different configuration of perforated aluminum sheets. I am working with radio waves but i am having am hard time finding any equations or properties for this ...
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0answers
41 views

Poynting of EM field and group velocity

Could anyone please show me mathematically how the poynting vector of an EM field is always parallel to its group velocity? I do understand the physical reason why it has to be the case, but showing ...
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3answers
66 views

Emission of EM radiation from an electron

I have read about an electron making a transition between two energy levels and electromagnatic radiation will be emitted. The problem is how and why e.m radiation is emitted.
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1answer
72 views

Why do physicists use a positive sign for the Fourier kernel / outward propagating waves? [closed]

I am not a physicist but rather an engineer / mathematician, so I've always wondered why is it that physicists use the positive sign convention in the forward Fourier transform. That is, in all of my ...
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0answers
58 views

Index of refraction for travelling EM wave problem

Let $n_1$ be the index of refraction of the first medium and $n_2$ be the index of the second medium. When $n_2>n_1$, then for an incident angle of $90^{\circ}$ we get a refracted light at a ...
3
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1answer
238 views

Refraction: Energy flow, tunneling and Evanescent EM waves

In the full internal reflection case where we have a refracted evanescent wave, If another object is nearby, then we could have wave tunneling phenomenon(frustrated total internal reflection). I am ...
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0answers
37 views

Gaussian beam with its waist lying on medium boundary

For $z<0$ the medium is air and for $z<0$ the medium has refractive index $n$ The waist lies on the $z=0$ plane with radius $W_0$. What is the solution in the medium? I take the distribution ...
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2answers
47 views

Photons reflecting off matter

When photons reflect off matter, do they always lose momentum to the object? If they lose momentum to the object, that means they lose energy, and so their frequency should decrease. However, when we ...
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1answer
61 views

Emission of Characteristic X Rays

X-rays are emitted when high velocity electrons in an X-ray tube collide with a metal target. Some high velocity electrons on collision with the metal atoms cause an inner electron of an atom to be ...
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2answers
2k views

Is it (practically) possible for a large building to be a Faraday cage?

In my sophomore year of high school, my P.E. teachers kept on complaining about how phones didn't have a network connection in our gym, regardless of model, service provider, etc. A couple of feet ...
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0answers
26 views

How long does it take for space dust to stop irradiating energy?

I heard that space dust is detectable because it irradiates on the infrared part of the spectrum? Does this happen forever? Won't it stop after some millions of years? Does it have to irradiate until ...
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0answers
30 views

What is the pure form of energy? [duplicate]

What is the pure form of energy? Einstein in his energy mass equation derivation said that electromagnetic radiation is pure form of energy.
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1answer
27 views

Understanding hollow waveguides. What is $\lambda_g$ on the figure?

I am trying to understand the field distribution in waveguides. On the figure is $HE_{12}$ mode of hollow fiber. What is the $\lambda_g$ ? Is it $\lambda_g$ = $\lambda_0$ / $n_{eff}$. Does the z ...
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3answers
1k views

If UV radiation 1 cm away from the halogen bulb is equal to Sun's radiation, what is the level of radiation 1 meter away?

Halogen light bulbs emit some amount of UV radiation, and some sources consider them dangerous. Here it is written, that UV radiation (of certain types) from a particular halogen bulb was equal to the ...
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0answers
40 views

Electromagnetic wave and intrinsic impedence [closed]

The electric field vector of an EM wave in free space is given by $$\bar E= \hat y [A\cos{\omega (t- \frac{z}{c}})]$$ where $ \hat y$ is the unit vector along the Y direction. What will be the ...
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2answers
65 views

Why wasn't the theory that light's velocity depended on its source very popular?

Before special relativity, it was believed that light having a specific velocity meant it had to travel through something. My question is, why wasn't the idea that light depended on its source very ...
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1answer
74 views

Electric field vector in visualization of polarization of EM wave

When we were taught polarization at the high school level, we were told that during polarization, we should consider the EM wave being axially or planarly filtered (e.g. by a polarizing sheet with ...
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2answers
58 views

Defining charateristic of light wave?

"Light is refracted when it travels from one medium to another." Does the sentence show that light is a wave?
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41 views

EM wave frequency and photon energy

We know that a quanta of light of frequency f has energy hf. But when I consider a single photon there is no concept of "frequency of a wave" because there is no EM wave associated with it which would'...
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1answer
34 views

Can we use a photon to use it as a changing field in an electric generator? [closed]

In an electric generator we use a changing magnetic field to create electricity. But what if we use a photon's oscillation of EM waves to generate electricity in a metal wire as we do in an electric ...
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1answer
93 views

Black Body radiation and Uv, x and gamma rays [closed]

Is the reason why UV, x-rays and gamma rays are non-existent on the blackbody radiation spectrum is because instead of the atoms present in the walls of the blackbody absorbing the energy, the energy ...
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1answer
51 views

What happens when the receiver of a parabolic antenna is covered by a metallic layer?

Out of curiosity I decided to conduct a small experiment and covered the receiver of the parabolic TV antenna with a metallic cylindrical food container without touching the receiver. It blocked the ...
20
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1answer
286 views

Should a superconductor act as a perfect mirror?

I have been told that metals are good reflectors because they are good conductors. Since Electric fields in conductors cause the electrons to move until they cancel out the field, there really can't ...
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2answers
202 views

Is there one all encompassing electromagnetic field? Or are electromagnetic fields separate and individually generated?

Many people have been using very confusing and sometimes contradictory language when describing electromagnetic fields and electromagnetic radiation. It's going to be hard to word this question so ...
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4answers
156 views

Why the electromagnetic waves propagate and do not stand still?

I know that the electromagnetic waves are alternating electric and magnetic fields. But I don't get why they can't stand still and alternate at the same point. I would like a logical and verbal ...
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1answer
58 views

What mechanism can we use to convert waves energy?

In term of renewable energy, can we use waves as another energy that can be stored and used instead of solar, wind and etc ? What I mean here is not sea waves but another kind of waves such as radio ...
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1answer
82 views

What role does wavelength play in the identity of a photon? [duplicate]

According to this question: What determines color -- wavelength or frequency? It is the energy, and thus the frequency of a photon $E=hf$, that determines where it lies in the electromagnetic ...
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4answers
145 views

reproducing double-slit experiment with sunlight

Is it possible to reproduce Double-slit experiment at home with sunlight probably in a larger scale? Thanks for all the answers (and special thanks to Chris for the effort),so i understand that it ...
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2answers
123 views

Maxwell equations and quantized electromagnetic field

When the electromagnetic field is quatized for a single mode, we first take Maxwell equations and proceed to write the electric and magnetic field as a stationary wave, since we consider the ...
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0answers
29 views

How does a dynamic electric field change a semiconductors carrier mobility?

Can an electric field that is spatially and/or temporally dynamic affect the carrier mobility in or on a semiconductor and, if so, how and to what degree? I appreciate any help or thoughts you have ...
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2answers
131 views

Why bremsstrahlung occurs only with the nuclei? Why not with the electrons?

In many books I read that bremsstrahlung effect (for e+) only occur when the electron goes near the atomic nuclei. Why is not possible when cross near an atomic electron? Thanks,
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1answer
42 views

magnetising the material using coil

I studied that when alternating current is passed through the coil ,the coil produce magnetic field (primary) as shown in figure,when any conducting material placed near to that field, eddy current ...
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1answer
132 views

how do photons move with respect to EM (I'd like to picture wave magnitudes frame by frame) [duplicate]

(I'm aware treating photon as particle and talking about its position is not exactly, conceptually right but I think it makes sense, at least in the point of view of a beginner. Please just assume ...
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1answer
41 views

Power and frequency of photons and its relationship with biological safety

I understand that x-rays are more dangerous than radio waves because they are of higher energy, since they have higher frequency. However, it’s less dangerous to stand near a radio station with a ...
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1answer
87 views

Can one make a propagating field along a waveguide only have longitudinal/transverse components?

We know that in free space, a propagating electromagnetic wave is always transverse. However, along a dielectric waveguide, the propagating wave can have longitudinal components. The exist of the ...
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1answer
98 views

Finding the range of frequencies to which a receiver should be set

I'm working on a study guide for a test for my Modern Physics class, and ran across a question I'm having trouble with. A radar transmitter emits a pulse of EM radiation with $\lambda=0.225\,\...
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1answer
46 views

Interactions of light with the air

This is an interesting thought which I had when driving home today looking in my wing mirrors. If you are driving a car and looking in your, say, right wing mirror, you see an image of the car ...
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40 views

Could there be ways to form hypergiant stars, quasars or supermassive black holes at the beginning of the Dark Ages?

Original title: Heat loss in collapsing parcels of gas or weak plasma at the beginning (not the end) of the cosmological dark ages Star formation from collapsing parcels of primordial gas in the late ...
2
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4answers
88 views

the relation between frequancy and energy of EM waves

In quantum theory, $$E=\hbar w$$ In classical theory, we have the Poynting vector: $$\vec{S_\space}=\frac{1}{\mu_0}\vec{E_0}\times\vec{B_0}{\cos}^2(kr-wt)$$ given S is energy flux density (the ...
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0answers
29 views

How to mathematically model a realistic aperture illumination?

I want to know a mathematical expression that I can use to model a realistic aperture illumination to produce the primary beam of an antenna so that the radial distribution of this aperture ...
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1answer
32 views

Rotation of polarization through optical activity

When a vertically polarized beam of light is incident on an optically active substance and rotated through some angle $\theta$, how is the degree of rotation related to the length of the path through ...