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Questions tagged [electromagnetic-radiation]

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

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Laser and Xray Wavelength

Calculate the wavelength of the xray emitted from a molybdenum target (z=42) when an electron moves from the L shell(n=2) to the K shell(n=1)
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Can a light absorbing bulb-like thing be made?

A bulb emits light. So can a bulb-like thing or anything be made such that it absorbs all/most of the light when turned on? For example, when room is dark we switch on bulb and it spreads light. Let ...
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77 views

What happens when the wavelength of light becomes as large as the observable universe? [on hold]

Say the wavelength of a photon became so large that it approached the size of the observational universe. Does something unexpected happen?
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18 views

What happens when a photon hits a particle (radiative heat transfer, photoelectric effect)?

By relating temperature to particle motion, the kinetic theory of gases gives an intuitive explanation of conductive heat transfer; faster particles collide with slower ones to transfer kinetic energy....
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26 views

Quantum Derivation of Electric Susceptibility

I've spent quite a while looking into classical models for electric susceptibility, including some semi-classical extensions to the idea, based around concepts such as effective electron mass. However,...
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29 views

Why alternating current produces electromagnetic waves? [duplicate]

So my question is: why alternating current produces electromagnetic waves? There are plenty of answers on google that state it as fact, but none answer why. I mean what is it about accelerating ...
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1answer
53 views

Why do the wavelengths of lights oscillate wrt atmospheric penetration?

Funnily enough, I was reading about Jungian Archetypes when I happened upon this diagram: I had not previously seen this and I couldn't find much information on it nor why it is occurring, I'd ...
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Emissivity and absorptivity relation question

This question is related to another discussion here about emissivity of bodies. What interested me is to verify what extend the wavelength between emissivity and absorption is conserved at thermal ...
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Gauge Invariance of Spin Angular Momentum of EM waves [closed]

How can I prove, the Spin Angular Momentum of Electromagnetic Wave to be not Gauge Invariant?
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81 views

How does an antenna capture the energy of EM radiation?

I am having trouble reconciling the descriptions I have read of how antennas work to recieve and transmit radiation. My simple understanding is that in recieveing the oscilating electric field of an ...
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How to find the fringe width of an interference pattern created by a spherical and a plane wave?

If we have two equations of a spherical and a plane wave (given that the plane wave is propagating along the $z$ direction), how do we find the fringe width of the interference pattern that would be ...
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3answers
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Why do we assume the reflected and transmitted waves are sinusoidal in the derivation of Fresnel's equations?

In the derivation of Fresnel equations, I often see the first step as writing down the equations of the incident, reflected and transmitted waves as sinusoidal. I understand why we do not lose ...
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Does superposition of all possible plane waves represent complete solution of Maxwell's equations in free space?

Consider the set of all possible superpositions of all possible "plane waves that satisfy Maxwell's equations in free space". Does this set represent all possible solutions of Maxwell's equations in ...
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Polarization on a spherical electromagnetic wave in free space using classical electromagnetism

The polarization of a plane wave traveling in free space is well defined and traverse to the direction of propagation from classical electromagnetic theory. Spherical waves are another type of ...
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1answer
45 views

What is the material property that controls the amplitude of the magnetic field oscillation? [closed]

What is the material property that controls the amplitude of the magnetic field oscillation in an EM Wave and how is it different than the material property for electric fields oscillation?
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5answers
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Does glass emit ultraviolet light?

I'm fully aware that glass absorbs light in the ultraviolet band. Moreover, glass does not absorb any light which has a longer wavelength than that of the UV light, making it transparent. This ...
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3answers
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Solution to Maxwell's equations in free space that are not plane waves [closed]

Are there solution to Maxwell's equations in free space that are not plane waves? I think there aren't. (Save trivial ones, i.e. E=const , B=const ) But i am not able to prove it. Please help. I would ...
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Electromagnetic wave in a prism

Imagine an electromagnetic plane wave entering perpendicular to one of the faces of a prism with the form of a triangle rectangle, which is made of a certain material of refraction index $n$. The wave ...
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2answers
58 views

Is it possible to create EM radiation moving in an opposite direction to that from an accelerated charge?

The Lienard-Wiechert retarded solution to Maxwell's equations has the radiation fields diverging and propagating away from an accelerating charge; the advanced solution has radiation fields converging ...
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Maxwell's equation in free space from wave equations of electric and magnetic field

How to go from the wave equations of electric and magnetic field and $$ \boldsymbol{\nabla}\cdot \mathbf E = 0 \quad \text{ and } \quad \ 0 = \boldsymbol{\nabla}\cdot\mathbf B, $$ to the remaining ...
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Velocity vectors during the propagation of photon in elastic scattering question [duplicate]

I have been trouble with the concept of energy of the photon during propagation in random scattered or random continuum medias. E = hf, where E is the energy of the photon in Joules; h is Planck's ...
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1answer
37 views

Question about quanta and $E=h\nu$

It is my understanding that Planck's major breakthrough was that energy comes in the forms of 'packets' called quanta, each of which has the energy of $6.62e-34$ of one Joule. By looking at Planck's ...
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2answers
60 views

What is the reason for the emission of electromagnetic waves from the sun? [duplicate]

What is the reason for the emission of electromagnetic waves from the sun and why curve its in about the visible light is maximum?
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37 views

Cavity optomechanics Hamiltonian

In cavity optomechanics the radiation pressure exerted by light moves a mirror in a cavity. Because of that the resonance frequency of the cavity changes due to change in length of the cavity (cavity ...
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2answers
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How do we get a expression for speed of light $\frac{1}{\sqrt{\mu\epsilon}}$ using Maxwell's equation? [duplicate]

I am a $12^{th}$ class student in India. I am quite new to these interesting concepts. And, I think I've learnt about electrostatics, magnetism, Maxwell's equations very thoroughly. But, my books ...
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What are common materials that absorb near infrared radiation?

I am running an experiment in my university lab where I want to compare with a sensor how much IR radiation gets transmitted in different scenarios. I need some (preferably common) materials that ...
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3answers
177 views

Can radio waves be harmful to us?

I was studying about Microwaves and their action on water molecules in heating up the food. This all is probably due to Microwaves have wavelength such that it can be absorbed by water molecules (am i ...
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2answers
276 views

Superposition of light waves of different colors

Can someone please assist? My question is regarding visible light. If, for example, red light and blue light are waves of different wavelengths and frequencies then how do they combine with all the ...
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What actually causes blackbody radiation? [duplicate]

I've spent a fair bit of time reading up on answers detailing exactly how blackbody radiation is created but I have seen two different explanations for how it is created. The Kinetic Energy (KE) of ...
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2answers
28 views

Why do we take the derivative of the number of modes with respect to frequency (Rayleigh-Jeans)

Source: http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/rayj.html We arrive at this result: $$N(\nu)=\frac{4}{3}\frac{\pi L^3\nu^3}{c^3}.$$ So now we have a function representing the number of ...
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30 views

Intensive and extensive properties

Is electromagnetic radiation flux (measured in watts per square metre) an extensive or intensive property? Can the fluxes from two sources be somehow combined at a target and what are the rules?
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2answers
64 views

Questions on derivation of Rayleigh-Jeans equation

So it starts by assuming a cube cavity with length $L$ that acts approximately as a black body. [note: the cube length is $a$ but I'm using $L$ instead] Standing waves are formed inside the cavity, ...
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1answer
48 views

Energy-frequency dependency of a photon and its medium of propagation

Is the equation relating a photon's energy to its frequency the same regardless of its medium of propagation? And for the equation relating its momentum to wavelength as well?
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33 views

Distribution of photons given an EM radiation

Given some EM radiation in vacuum, how can we calculate the probabilities or distribution of photons of different wavelengths? How might the results of the calculation change if the entire radiation's ...
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1answer
44 views

Microwaves in other media

I saw a video on how microwaving grapes make plasma. He said that the refractive index of microwave is about 10 inside the grape. Now, we don't know the wavelength of the microwaves in the grape or ...
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Electric field and particle Vibration

Electromagnetic waves are produced when particles vibrates, then why the direction of electric field is considered normal to the direction of propogation of wave? When electric field vector always ...
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1answer
52 views

Why protons and electrons attract each other? [duplicate]

This YouTube video states that electrons and protons are bonded together by emitting electromagnetic waves and absorbing each other's electromagnetic waves. But isn't because it due to potential ...
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5answers
332 views

Does classical electromagnetism really predict the instability of atoms?

I will try to give a concise summary of what I wrote below. I understand that it is very long and apologize if I am wasting your time. I used the Liénard-Wiechert potential and the Lorentz force ...
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2answers
169 views

Why doesn't there exist a wave function for a photon whereas it exists for an electron?

A photon is an excitation or a particle created in the electromagnetic field whereas an electron is an excitation or a particle created in the "electron" field, according to second-quantization. ...
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Re-Radiation from a ferrite rod antenna: Phase relative to the incoming signal

I am working through a problem involving interactions between multiple closely located ferrite bar antennas. I am seeing energy re-radiated from the various antennas coupling into the other ...
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1answer
59 views

What's the difference between linearly polarised and plane-polarised waves?

To explain polarisation, my book gives an example of a transverse wave in a string, and explains as: Since each point on the string moves on a straight line, the wave is also referred to as a ...
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2answers
75 views

How does Destructive Interference redistribute energy?

I have tried looking at the many other questions on a similar topic, however, they don't provide a definitive answer to my question. What I managed to gather so far, is that if a light wave is super ...
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Is there a chart/list showing the velocities of electrons that produce different types of EM radiation?

Is there a reference guide of sorts showing the voltages of x-ray tubes, radio-wave generators, etc.? That produce waves/photons of a given frequency or eV? Or the velocities of the electrons or ...
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Refraction of a circular polarised wave

I'm trying to derive the expression for the fields $E_{1}$ and $E_{2}$ in terms of $n_{1}$, $n_{2}$ and $E_{0}$. Where: $E_{0}$ Is the incident field amplitude of circular polarised light $E_{1}$ Is ...
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1answer
45 views

Is discharge tube dangerous?

Are those gas discharge tubes dangerous? I found atom spectra interesting, so I booked a 1.5 hour lab session at a local high school. The physics teacher gave me a few hydrogen tubes, helium tubes, ...
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2answers
34 views

Factor of 4 discrepancy between integral of Planck's law vs Stefan-Boltzmann law

Consider an absolutely black sphere with unit surface area and temperature $T$. Planck's law states for the power emitted per unit area of the emitter per unit solid angle of emission per unit ...
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0answers
32 views

How can microwave radiation penetrate through walls but visible light cannot? [duplicate]

Obviously cell phone microwaves can penetrate more than just the walls of the house or an elevator...etc, why can't visible light at any strength penetrate the same objects?
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3answers
105 views

Can High Energy Light Escape a Black Hole after Low Energy Light Cannot

Perhaps there is another way to calculate the escape velocity, or perhaps light always has the same kinetic energy regardless of the energy of the light, but shouldn't the event horizon of a black ...
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Is it possible for electromagnetic waves in the Extreme Low Frequency range to carry HQ video and audio signals? [duplicate]

I had just finished this interesting read on a us navy project and was wondering how Brain computer interfaces are touting in the near future to pick up thoughts that might need the same bit rates as ...
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The rise of BCI

If EEG and MEG are measuring different aspects of neural oscillations, why can't we measure the combined signals as a whole, when we are doing the same for higher frequencies? Why did the us navy ...