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 (1)

2
votes
2answers
1k views

How much better is salt water at letting through microwaves than pure water?

Radio Wave Attenuation There are two general types of matter (substances) in the universe that affect electromagnetic waves, conductors and insulators which are called dielectrics by ...
1
vote
0answers
27 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 ...
1
vote
0answers
45 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. ...
0
votes
2answers
81 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 ...
0
votes
1answer
33 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 ...
1
vote
0answers
51 views

What does matter wave oscillate? [closed]

We know by Maxwell equation, light is an Electro-magnetic wave, the light is oscillating the magnetic field and electric field and propagate Sound will oscillate the air, water, or whatever and ...
3
votes
1answer
171 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 ...
0
votes
2answers
118 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 ...
11
votes
3answers
17k views

Why do lightbulbs continue to glow after the light is turned off?

I've noticed that whenever I turn the lamp off in my room at night, the lightbulb seems to continue to glow for a minute or so after that. It's not bright though; the only way I even notice it is if ...
0
votes
2answers
54 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?
1
vote
1answer
63 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 ...
2
votes
5answers
2k views

Why do photons travel?

Photons travel at the speed of light. Is there a known explanation of this phenomenon, and if yes, what is it? Edit: To be clearer, my question is why do photons travel at all. Why do they have a ...
3
votes
1answer
482 views

AM vs FM radio under bridges

I know what the difference between AM (Amplitude Modulation) and FM (Frequency Modulation) radios is. However, I noticed that when I drive under a bridge while listening to a station on AM, it just ...
-3
votes
2answers
67 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?
0
votes
0answers
11 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 ...
1
vote
0answers
38 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 ...
0
votes
3answers
33 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.
5
votes
3answers
5k views

Why do electromagnetic waves oscillate?

I've been considering this question, and found many people asking the same (or something similar) online, but none of the answers seemed to address the core point or at least I wasn't able to make ...
0
votes
0answers
45 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 ...
11
votes
5answers
816 views

What direction does the evanescent wave point?

On wikipedia they say that the evanescent wave has a magnitude of: $$E=E_0 e^{\alpha y-j\beta x}$$ Where $j=\sqrt{-1}$, but what direction does this vector point in and why? (let us say the boundary ...
0
votes
0answers
26 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 ...
5
votes
1answer
181 views

Why is the wave equation so pervasive?

The homogenous wave equation can be expressed in covariant form as $$ \Box^2 \varphi = 0 $$ where $\Box^2$ is the D'Alembert operator and $\varphi$ is some physical field. The acoustic wave ...
0
votes
2answers
39 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 ...
18
votes
2answers
4k views

How do microwaves heat moisture-free items?

Today I learnt that microwaves heat food by blasting electromagnetic waves through the water molecules found in the food. Does that mean food with 0% moisture (if such a thing exists - dried spices?) ...
0
votes
0answers
33 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 ...
2
votes
5answers
275 views

Why is diffraction related to wavelength, not amplitude?

For diffraction, the wavelength of the incident beam should be in range magnitude of the slit length, but why the isn't the amplitude related to the length of the slit?
4
votes
4answers
2k views

Do Electromagnetic Waves really propagate through continuous Induction?

I've often seen it said that in an Electromagnetic Wave the changing Electric Field component creates the Magnetic Field Component and the changing Magnetic Field Component in turn creates an Electric ...
23
votes
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 ...
3
votes
1answer
6k views

Intensity of unpolarized light through polarizer

When unpolarized light is polarized with two polarizers, the intensity becomes $I=I_ocos^2(θ)$ (Malus's law). But when unpolarized light is polarized with only one polarizer, the intensity is reduced ...
0
votes
0answers
25 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 ...
0
votes
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.
1
vote
2answers
146 views

Gamma Ray Bursts

What is the maximum frequency of the Gamma Rays produced during supernovae? And how are these detected by telescopes without getting some serious damage done?
7
votes
0answers
121 views

Experimentally diminishing random errors for low wavelength UV observations

Part of the work that I do involves observations of solar low wavelength UV observations, specifically UV-B and UV-A II (up to 340nm). I have noticed that when I observe responses on a CCD or CMOS ...
7
votes
1answer
349 views

Orbital angular momentum of photon

People talk about orbital angular momentum (OAM) of photons. Is there some physical example that cannot be explained without assuming that photons have non-zero OAM? Does different photons have ...
2
votes
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 ...
4
votes
2answers
1k views

Linear vs. quadratic dispersion relation

In wave mechanics the dispersion relation between frequency $\omega$ and wave number $k$ is linear: $$\omega_n=c k_n$$ But in quantum mechanics, based on Schrödinger's equation, one can show that we ...
2
votes
1answer
347 views

Would there be EMF induced in our body due to electromagnetic radiations?

The experiments of innovative Faraday and Joseph Henry in USA, conducted around 1830, demonstrated conclusively that electric currents were induced in closed coils when subjected to changing magnetic ...
2
votes
1answer
23 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 ...
0
votes
2answers
63 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 ...
1
vote
1answer
98 views

Is it possible to create arbitrary shapes of magnetic fields?

I've been reading about Transcranial Magnetic Stimulation (TMS) which can activate neurons using a magnetic field, which got me thinking... what if we can pick and choose exactly which neurons to ...
4
votes
2answers
2k views

Make a semi transparent mirror with copper

The question: How would you make a semi transparent mirror (50% reflection, 50% transmission) with glass with a layer of copper. For light $\lambda$ = 500nm Try to be as realistic as possible What ...
2
votes
0answers
37 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 ...
1
vote
1answer
51 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 ...
0
votes
0answers
32 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 ...
17
votes
1answer
204 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 ...
7
votes
2answers
707 views

Does light really “travel”?

From what I've so far understood about light, a photon is emitted somewhere and after some time it's absorbed somewhere else. Have we had experiments that confirm the path taken or something akin to ...
0
votes
1answer
39 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 ...
1
vote
1answer
32 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 ...
1
vote
1answer
49 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 ...
2
votes
1answer
1k views

Why does friction produce heat?

What causes two objects sliding against each other to produce heat? Why don't they generate visible light or something else?