New answers tagged electromagnetic-radiation
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Why does the kink has the following vector direction?
Electric field associated with moving charge shows what happens when a charge starts at rest and suddenly jerks to a new position and stops. This isn't very realistic, but it is easier to understand ...
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How do EM waves interact with one another?
EM waves pass through each other. When they reach a solid surface they can interfere constructively (the waves add together) or destructively (the waves cancel out).
This is easiest to see with two ...
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How do EM waves interact with one another?
A crucial characteristic of electromagnetic waves is that in everyday circumstances they can pass right through one another without any disturbance. This means that light sources from all the lit-up ...
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Light wave/photon doppler effect
In the photon picture, the Doppler effect manifests itself in two ways. Assuming the source and observer are moving away from each other,
The rate at which the photons arrive is reduced. This happens ...
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SETI: Are there holes in the EM spectrum that are quiet enough to communicate at decently large distances?
Most of the spectrum is similar to that of a blackbody.
The quietest portion is up in energy, in the soft x-rays and up. And the low energies (radio waves) are comparably quiet compared to ...
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Experiment to determine if a photon is emitted in one direction
Most nuclear physics experiments deal with precisely the kind of experiment you’re proposing. They have an array of photon detectors around the sample and they look at the angular distribution of ...
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Interference of polarized light
There are plenty good answers already but I want to point out something that most other answers have missed and something Vladimir Kalitvianski was alluding to in their answer. If you want to skip to ...
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Speed of EM Waves
The gold (or whatever) atoms/ions experience the radiation as an oscillating electric field.
The atomic electrons oscillate in response. The size (and phase) of their response depends on the detail of ...
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Speed of EM Waves
Feynman chapter 23 Refractive Index of Dense Materials in his Lectures Volume 2 explains the fact that the permittivity of a material is frequency dependent (and can be imaginary!) as is its ...
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Why is the direction of polarization of EM wave is the direction of Electric field?
It is a natural choice because the $B$ field is not a vector in the usual sense, but rather it is a bi-vector representing a plane of action coincident with the polarization vector of the $E$ field. ...
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Why is the direction of polarization of EM wave is the direction of Electric field?
It's a semi-arbitrary choice. Not completely arbitrary since, in practice, we more commonly sense EM waves by their electric fields rather than their magnetic fields.
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How can things around us have different colours if they have specific emission spectra?
Atomic hydrogen gas does glow with a particular colour, as long as it is at sufficient temperature to excite some of its atoms into excited levels. Here is an example:
First an RGB image taken with ...
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How can things around us have different colours if they have specific emission spectra?
H absorbs very specific wavelengths, leaving almost all wavelengths undisturbed. Also the excited atoms then decay, producing the same wavelengths that were just absorbed.
Those wavelengths are the ...
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Radiation in an ideal LC circuit
You are correct. There is indeed loss of energy in an LC circuit due to exactly the process you mentioned. However, I would say this loss of energy tends to be negligible in most common situations, so ...
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Derivation of the Eddington limit
Looking at a small bandwidth $\delta\nu$, the integral captures:
$$ \frac{L_{\nu}\delta\nu}{h\nu} $$
The numerator is total power radiated in this bandwidth, and the denominator normalizes that to a ...
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The Classical Theory of Fields: Surface Integral of Poynting Vector Vanishes at Infinity on page 76
Indeed, the if-then statement is incorrect in general. The surface integral can be non-zero in infinity, and it can also be zero at infinity. We can't check this directly so we should not claim it is ...
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The Classical Theory of Fields: Surface Integral of Poynting Vector Vanishes at Infinity on page 76
You are right! In the case of radiating sources in the finite both $\mathbf E$ and $\mathbf H$ are $\mathcal O(R^{-1})$ and the integral $\oint \mathbf E \times \mathbf H \cdot d\mathbf f$ is finite ...
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Do electromagnetic antennas transmit (unintentionally scatter) when they receive?
If you could recreate the full electromagnetic field of a matched antenna that it creates when in transmit mode than it would not scatter in its receive mode, this is reciprocity. Note the emphasis on ...
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Do electromagnetic antennas transmit (unintentionally scatter) when they receive?
Free electrons in the antenna are made to oscillate by the oscillating electric field in the incident wave. The oscillating (and therefore usually accelerating) electrons emit electromagnetic waves. ...
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What are the average wavelengths and brightnesses of sunlight across the stages of twilight?
There are illuminance data per half-degree of solar elevation at twilight available on Paul Schlyter's page, but nothing on colour spectrum. Computer graphics researchers (Bruneton & Neyret) have ...
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5G networks and health concerns
Technically speaking, there is very little to be concerned about 5G if you compare to all other radiations that are around us, including wireless bluetooth headphones and pre-5G technology. In the ...
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How do surfaces absorb and reflect light at the atomic level, and what does that have to do with color?
Light is an wave in the electromagnetic field. It's useful to model light as being made up of many little superposed waves, each with a particular specific energy amount. The energy amount of each ...
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Why can a beam of electron and not scatter with a proton to form a H atom?
Consider the center of momentum frame. In this frame, the electrons with mass $m_{e}$ have energy $E_{e}$ and momentum $\mathbf{k}$. The proton has mass $m_{p}$, energy $E_{p}$, and momentum $-\mathbf{...
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Why not use Bose-Einstein Statistics to derive the Planck's blackbody radiation law?
Planck's Law is the first place BE statistics shows up, and so it is necessary to have some way to derive BE statistics.
It is not just that we are treating each QHO separately, but that we are also ...
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Doubt in the definition of intensity
Like I indicated in a comment, that is not how radiant intensity is defined, nor does it have the correct units for radiant intensity (it should be $\text{W/sr}$). But you seem to be talking about ...
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Hidden momentum
In general "hidden momentum" is simply the statement that electric charges induce a extra momentum for the electromagnetic field. So when considering momentum conservation one has to take ...
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Refractive index of EM waves travelling though a gas of neutral particles
The oscillating EM fields that cancel the vacuum speed wave, can be originated by neutral particles that are polarised, like neutral atoms. Read about the Ewald–Oseen extinction theorem.
The charge ...
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Understanding blackbody radiation
Here is a more correct and hopefully easier way to visualize the process.
What is wrong here is the basic idea that the walls of the cavity are perfect reflectors of EM radiation. They are not. They ...
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Understanding blackbody radiation
Perfectly reflecting cavity is not a blackbody. However, if inside the cavity there is some piece of absorbing matter, then a small hole in the cavity will behave as black body. The piece of matter ...
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Would dipole antenna work in the following case?
I guess you mean a periodic voltage pulse sequence, say $$s(t)=A \text{ when } 0<t<dT_p, \\p(t+T_p)=p(t) \\\text { and } p(t)= 0\text{ otherwise}$$ and $0<d<1$. This can be expanded in a ...
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What causes the Faraday effect, on a material level?
I think you want to look into what happens to paramagnetic impurities in something like flint glass, or if it a gas in optical cell, the paramagnetism of the gas.
If there is an unpaired electron, ...
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What is the physical significance of crest and trough in an electromagnetic wave?
Let's start with mechanical waves. Wave Machine Demonstration. This Jelly Baby wave machine shows that if you move one Jelly Baby up and down, you create a wave that moves away. The crest and trough ...
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Electric field of dipole antenna
In the farfield where the E-field is propagating as a transverse EM wave, it will interact with your charged particle causing the particle to move in the direction of the E-field. Because of this, the ...
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Do blackbodies emit gravitational waves?
Recall the essential steps that allow statistical mechanics to derive things such as black-body radiation and other thermodynamic phenomena:
There is an idealized system known as the microcanonical ...
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Why does redshift happen?
Would you agree with me that this is the reason and correct logic why redshift happens?
Yes.
It's just that redshift means the change factor, not the change.
One nano-meters change is a large change ...
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Compton scattering with free electron
The "low energy limit" of Compton scattering is called Thomson scattering, which occurs when the energy of the photon $E_\gamma \ll m_ec^2$. Since $m_e c^2 = 511$ keV, then this condition is ...
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Compton scattering with free electron
If everything is correct above, could we assume that even visible light photon could cause the compton, it's just we don't care if it does as the difference in wavelength is so small, we neglect it?
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Compton Scattering Notion
The terminology is a bit murky. We call the interaction of photons with free electrons "Thomson" scattering if the electron recoil is small enough to be neglected. This is true for visible ...
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How does inner Bremsstrahlung work?
By definition, inner bremsstrahlung is arises from the creation of the electron and its loss of energy (due to the strong electric field in the region of the nucleus undergoing decay) as it leaves the ...
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What are the underlying concepts of the wavelength?
Recently I was doing my homework and I found out that in the electromagnetic spectrum, $f = c / \lambda$, where $f$ is the frequency, $\lambda$ is the wavelength, and $c$ is the speed of light.
Why ...
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What are the underlying concepts of the wavelength?
By definition, the frequency of oscillations is the inverse of the oscillation period:
$$ f = \frac 1T \tag 1$$
Multiplying the numerator and denominator by the speed of light, we get:
$$ f = \frac {c}...
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How to calculate the change of the density of photons in different frames?
In the second frame, the volume you are measuring is Lorentz-contracted compared to the first. This means that the number density of the photons changes. In other words, the change in the energy ...
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What happen to the electromagnetic waves when a photon's "wave function" collapses?
Let's say we have one EM-wave sending antenna and two identical receiving antennas.
When it happens that for one millisecond one antenna receives no energy and the other antenna receives double the ...
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Is light dark energy?
Leon mitchell's suspicion is correct. Space is simply light pressure, a spherical explosion of overlapping propagating electromagnetic waves. There is a direct correlation between the amount of EM ...
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