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

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1k views

Why are EM waves transverse?

I was reading Griffiths' Introduction to Electrodynamics, specifically the section on plane waves. I can see that if we want a transverse wave traveling in the $z$ direction that we are only going to ...
3
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2answers
644 views

Who discovered that electromagnetic wave doesn't need a medium?

I have read that physicists in 19 century searching for the aether. They thought that light must have some medium to carry. When did they know that light and other electromagnetic wave doesn't need ...
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1answer
116 views

Electromagnetic interaction physical interpretation [duplicate]

Why do radio waves, X-ray and gamma rays penetrate through matter? Can anyone explain me this in terms of incident energy or wavelength of the photon and the effective cross-section that these photons ...
2
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1answer
311 views

Why is a particular wavelength favored by transmission through a thin film?

A sheet of glass is coated with a $500\text{ nm}$ thick layer of oil ($n=1.42$). For what visible wavelengths of light do the reflected waves interfere a) constructively? b) destructively? ...
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2answers
600 views

What is the difference between xrays and ultra violet rays?

Do they differ in just frequency and wavelenght ? Or there is more about it
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1answer
47 views

A confusion on Radiations emitted from a body [duplicate]

Suppose an atom is accelerated...Now the protons in its nucleus and the electrons in the orbits are also accelerated...So will they emit the electromagnetic radiations? Basically here the electrons ...
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1answer
59 views

How can we derive that an accelerated charge particle will radiate EMWs?

All the properties of the electromagnetic entity is said to be fully described by the four golden rules of Electromagnetism : The Maxwell's Equations.How can we derive that a charged particle will ...
7
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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 ...
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0answers
80 views

Is a smartphone with a radar possible? [closed]

Is any form of radar possible with the sensors in an iPhone 5s ? Could you use the speaker and microphone to do sonar?
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1answer
963 views

When is the displacement current equal to conduction current in case of a parallel plate capacitor being charged?

I came across a text - "Whenever a conduction current is oscillating in time, the displacement current is equal to the conduction current in case of parallel plate capacitor." I am not sure what's ...
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0answers
88 views

What is the highest frequency directly detected?

The Feynman Lectures of Physics states: In fact, although we mentioned many frequencies, no phenomenon directly involving a frequency has yet been detected above approximately $10^{12}$ cycles per ...
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3answers
113 views

Difference between high-level and low-levels of electromagnetic radiation

can someone please explain me what we mean by 'high-level' or 'low-level' in electromagnetic radiation? for example, it is believed that high-level microwave radiation is harmful to human but not the ...
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0answers
89 views

How is Energy Distributed within a Electromagnetic Wave?

Let $$\hat{H}$$ Denote the full energy of the electromagnetic wave. Now is it right to assume that $$\hat{H}=\sqrt{2\hat{H}_y^2+\hat{H}_x^2}=\sqrt{2\hat{H}_z^2+\hat{H}_x^2}$$ If not, what is ...
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2answers
1k views

Can someone explain to me the concept of atmosphere opacity?

On this diagram, why is the atmospheric opacity shaped as it is? If we are able to see lights due to low atmospheric opacity, why can't we see radio waves, when the atmospheric opacity is so low ...
2
votes
1answer
165 views

Electric charge of light? [duplicate]

Light (or any radiation as a matter of fact) is an electromagnetic wave so why doesn't it have a electric charge associated with it? As far as I know only static or flowing electric chargers can ...
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1answer
103 views

Is the photon first a wave, then a particle? [duplicate]

When the 'photon' is emitted, it would reason that the result of the energy fluctuation that creates 'it' rather is created as an energy wave, which when measured by us or a surface, it 'becomes' as a ...
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2answers
122 views

Internal energy and photon absorption

I just wish to confirm whether my understanding is correct. I know that photon absorption/emission brings about quantised changes in electron energy levels. Photons (infrared) also interact with ...
0
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2answers
100 views

How hot particles can get [duplicate]

One way in which an object is affected by temperature rise is that the wavelength of the radiation it emits is gets smaller and smaller. Another way of looking at it is that as an object gets hotter, ...
3
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2answers
100 views

Blackbody radiation through quantum mechanics perspective

While explaining black body radiation, the body is assumed as a cavity radiator and the radiations are due to the oscillating electrons. But we know that the electromagnetic radiation emitted is ...
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2answers
516 views

Is data which rides on the carrier frequency dangerous?

My understanding of broadcasting data via electromagnetic radition is, that the data "rides" on a carrier frequency on which it is radiated. I am aware of the fact, that those carrier frequencies are ...
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1answer
85 views

Can we multiply an electromagnetic field?

can we multiply light by a sequence of reflections in a closed vessel? also, is light a part of EM wave? can we multiply the radio wave or EM wave from a transformer?
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0answers
28 views

Can various wavelengths participate in C/D Interference?

My question is can multiple wavelengths or at least two different wavelengths interfere with one another? I know that they usually have to be the 'same' wavelength, but you'd think they can vary a bit ...
0
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1answer
2k views

If sound travels through matter what medium does light travel through? [duplicate]

So sound is a wave and is basically just vibrations, an atom vibrates causing another next to it vibrate and so on until it finally reaches our ears to become sound. If that's normally how waves ...
0
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2answers
250 views

Parallel electric and magnetic field in traveling wave

Can we have elctromagnetic waves which are characterized by parallel electric and magnetic field $\vec{E} || \vec{B}$ ? I am not talking here about free space, but maybe some kind of materials or ...
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2answers
190 views

Why group velocity represents energy or information transmission? What relation between phase velocity and special relativity

I have two question, why group velocity represents energy or information transmission? what is the relation between phase velocity and Special relativity: why can it exceed C without violation of ...
2
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1answer
836 views

Dark matter a medium for light propagation

Is dark matter a candidate to fill void left by luminiferous ether as a medium for light travel?
3
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1answer
128 views

What does a supernova look like at its peak luminosity?

I know that in some types of supernovae, the cause of the increased luminosity is the radioactive decay of certain elements ejected during the explosion, so a question came to my mind. If the ejected ...
6
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1answer
3k views

What is the meaning of this “let there be light” joke?

Someone across the restaurant is wearing this shirt, and I certainly don't get it. Update Related: What does this quote about the four dimensional divergence of an antisymmetric tensor mean?
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1answer
536 views

How to calculate the differential scattering cross section?

I am doing some simulations with the Meep code to study some properties of a metal nanoparticle. The situation is this: an incident electromagnetic wave on a metal nanoparticle. By now I know how to ...
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1answer
145 views

What would a laser beam's E-M waves actually look like if you zoomed in?

I am trying to understand how a real world beam of laser actually reflects the physics description of oscillating electromagnetic waves. So say we are looking side on at a vertically polarized laser ...
3
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1answer
341 views

Why would a rotating charged sphere not have time varying electric field?

I have seen Gauss Law being used for a uniformly charged hollow sphere rotating with $\omega$. How is that valid to use Gauss law since it is an electrostatic law and if it is valid, why do we get a ...
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1answer
58 views

The difference between EMR and lone Electric and Magnetic fields

I fail to understand the true difference between EMR and electric and magnetic fields. When current flows, there is an electric field due to the electron flow and a magnetic field, however no EMR ...
2
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2answers
203 views

Why does the second Weyl scalar describe electromagnetic radiation?

I've been reading about the null tetrad, the Weyl tensor, and the Newman-Penrose identities, and so I found out about the Weyl scalars. While the zeroth, first, third, and fourth scalars describe ...
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2answers
177 views

Angular momentum of light

Can someone explain the classical angular momentum in electromagnetic theory of light? If I shine elliptically polarised em wave on a black disc it rotates. I would like to know how to calculate ...
0
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3answers
623 views

Visualisation of formation of electromagnetic waves [duplicate]

Recently I am studying electromagnetic waves, and I am wondering why it is formed by acceleration of electric charges? Can the EM waves be formed by other movements of electric charges, such as at a ...
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5answers
245 views

Sequence of E and B field in radio waves and in single photons

In antenna technology we distinguish between nearfield and widefield. In the nearfield the electric and the magnetic fields are shifted by 90°. If you look closer you can see that there are two ...
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0answers
100 views

Poynting Vector Volume Integral Inside a Cavity

Given an electromagnetic wave in resonance mode in a vacuum cavity inside a perfect conductor, on the boundary, the parallel component of $E$ field vanishes, and the perpendicular of component of $B$ ...
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3answers
325 views

Which electromagnetic radiation is faster in water, microwaves or light?

Well I've been asked this question, but I haven't been able to come with an answer yet using books and some web searches. The point is as the title says, to answer the question with the whole ...
2
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1answer
63 views

Accelerating masses lose energy?

If I understand this correctly, accelerating charges lose energy in the form of EM waves because they change the electric and magnetic fields, which "costs" energy. Does that mean that accelerating ...
0
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0answers
40 views

Band-limited double-step Fresnel diffraction for images with radio waves?

Is it possible to use band-limited double-step Fresnel diffraction to assemble a holographic image with radio waves? If not is there a simular principle?
2
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2answers
149 views

Why do the electron in Bohr's principal quantum levels or ground state do not emit radiation? [duplicate]

Bohr said that only certain orbits of definite energy are allowed inside the atom. He said that the electrons in their ground state do not emit radiation and that they will emit radiation when they ...
2
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3answers
377 views

What exactly is Electromagnetic Radiation?

I don't understand how and why the electric and magnetic fields oscillate in the electromagnetic radiation wave, and any way where do these fields originate from, for there are no charged particles in ...
3
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3answers
315 views

Why does $\nabla \to ik$ when you Fourier transform?

I am reading a text that describes the scattering of light by a particle with dielectric constant $\epsilon$ After a bit of maths starting from Maxwell's equations they obtain: $$\nabla (\nabla ...
4
votes
2answers
327 views

Finding the cosmological redshift of a galaxy in the expanding Universe

Firstly, I understand what the Doppler effect is when it comes to sound or light waves. From everything that I've read, we are told that the universe is constantly expanding since the all the ...
2
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1answer
64 views

Electromagnetic fields and human behaviour

To what extent does electromagnetic fields and/or radiation from space have influence on human behaviour and/or physiology?
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1answer
91 views

Is it possible that matter/antimatter collisions emit resonance frequencies of H/He?

Is it possible that matter/antimatter collisions emit resonance frequencies of H/He? I am researching a high energy phenomenon that occurs between the frequencies of 1200-1580 MHz. This come from a ...
8
votes
3answers
1k views

Why can't light penetrate solid objects?

Light is combination of perpendicular electric and magnetic fields, since electric fields penetrate a conductor, why can't light travel in them? I think my argument does sound stupid, but I can't ...
2
votes
1answer
481 views

Why does the speed of the Electromagnetic wave in the material depend on the frequency of the wave where as they are constant in vacuum (freespace)? [duplicate]

I am confused on why would the propagation speed of any EM waves at ANY frequency is constant in the free space (vacuum) but they seem to disperse in any other materials as the propagation speed of EM ...
2
votes
3answers
2k views

How does the movement of electrons produce radio waves?

I'm mostly wondering about radio frequencies. I understand that voltage is the movement of electrons, and that the antenna acts as a light bulb, emitting at radio frequencies, following the reverse ...
17
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2answers
925 views

Why is Huygens' principle only valid in an odd number of spatial dimensions?

Apparently Huygens' principle is only valid in an odd number of spatial dimensions: http://mathoverflow.net/a/5396/21349 Huygen's principle in curved spacetimes Why is this? [EDIT] This is ...