All Questions
Tagged with electromagnetic-radiation photons
622
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Link between photon helicity and polarization of $A^\mu$ electromagnetic potential
From Wigner theorem we know that the irreducible unitary representation of the Poincarè group for massless and spin 1 particle is labelled by the momentum $p_\mu$ and the two possible helicity $+1,-1$ ...
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1
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Why does radiation of small wavelength interact with small objects?
I was reading chapter 2 from the book 'Diagnostic Radiology Physics : A handbook for Students and Teachers', and came across the following quote
"X rays of energy of a few tens of ...
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3
votes
3
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182
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Photonic black holes
"Can a photon turn into a black hole?" - usually the answer to this question is - it can't, because it has zero rest mass. However, when we derive the Schwarzchild Metric initially the $2M$ ...
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How many photons pass through us every second?
I just read this answer https://physics.stackexchange.com/a/229374, which says that, when a magnet rotates, photons are emitted with wavelength $λ=c/f$, where $f$ is the frequency of rotation. And ...
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Is luminescence from impact of fast neutral atoms/molecules on a suitable substance known?
Cathodoluminescence is emission of photons by electrons impacting on a luminescent material.
The Rutherford scattering experiments detected impacting helium nuclei on a phosphor screen.
Many other ...
- 1,421
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answer
87
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What is light? how is it connected to electromagnetic radiation?
I am trying to understand how light works and electromagnetic radiation, from what I understand charges cause disturbances in electric fields, which triggers a magnetic field, and then the back and ...
2
votes
1
answer
54
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Is energy contained in/transferred by light really discrete or is it continuous? [duplicate]
I don't really understand the wave-particle duality of light.I don't really understand the idea of photon, The idea of photon that is generally taught is that it is a fundamental unit of light with ...
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2
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112
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Single photon detection
Consider a thought experiment where we have a source emitting a single photon, like an atom/molecule going from an excited energy state to its ground state.
We have an infinite number of point ...
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1
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If helicity of photons is +1 then the light is right- or left-circularly polarized?
In particle physics, we say: a particle has +1 helicity (right-handed) if its momentum and spin are parallel, or it has -1 helicity (left-handed) if its momentum and spin are antiparellel.
Now, if we ...
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97
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How does a photon look like in QFT? [closed]
It is very well known that in QFT the particles are excitations of the field. But how exactly is a free photon looking like in spacetime? What is it shape in free space? And what is in fact in the ...
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1
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84
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Photon propagation paradox, what am I missing? [closed]
I've seen photons and EM waves be described like so "Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields."
So if we have a ...
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31
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Behavior of a single emitted photon [duplicate]
Suppose you have a transmitter sending out a single photon. If you think about this photon as a wave, you will see a circular wave moving away from the transmitter. Over millennia, this wave spreads ...
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1
answer
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What fraction of the universe's energy is contained in photons?
From each point in the universe, the light of billions of stars, galaxies, supernovae etc. can be detected. So there seems to be a lot of energy/momentum "in flight".
Is it possible to ...
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0
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32
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What is the speed of light during reflection? [duplicate]
What is the speed of light in a vacuum when the light reflects off of a mirror?
- 331
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1
answer
53
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Photons and Bremsstrahlung radiation
When fast electrons goes into a target, part of their kinetic energy is converted into electromagnetic radiation, that we call Bremsstrahlung radiation, as they change their velocity. The energy ...
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3
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1
answer
109
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How is it possible that photons already move at the speed of light the moment they pop into existence? [duplicate]
This is a thought experiment and I might be horribly wrong. If we have an electron-positron annihilation a photon pops into existence. This photon is then supposedly moving at speed of light at the ...
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2
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143
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Analogy between the Electromagnetic Field and the Schrodinger Equation
In this answer my2cts says "The electromagnetic field is to photons what the Schrödinger or Klein-Gordon wave function is to electrons." Could someone expand on this further? Is this just a ...
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2
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Are EM waves telling us the probability of finding a photon?
I feel like I've been frequently presented with an interpretation of EM waves that goes something like this:
Light is an oscillating electromagnetic field. Because changes in the electric field ...
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2
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84
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Emission of a single photon
When a single photon is emitted as a result of an electronic transition, it will have a defined energy and wavelength. However, its amplitude is not constant over infinite space and time; instead, it ...
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3
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What is the difference between photons and electromagnetic waves?
Electromagnetic waves are generated by accelerating electric charges.
Photons on the other hand, tend to describe something different, specifically the particle nature of electromagnetic waves as ...
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2
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63
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Which factors determines whether a photon is absorbed? [duplicate]
After some research, I figured out that all EM waves/photons are absorbed by atoms by exciting an electron from an orbital to an other. However, atoms emit only certain EM waves with specific ...
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1
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87
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Why does there need to be a particle representation of light?
Why does there need to be a particle representation of light? Doesn't light as a wave explained the observations of the photoelectric perfectly? When the frequency of light is increased, the speed of ...
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2
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162
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Electromagnetic field affect on hydrogen atom energy levels
If hydrogen atom is in the ground energy state it must be hitted by photon with energy higher than electron proton energy binding which is 13,6 eV according quantum mechanics. Proton have positive ...
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2
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How does a photon "cheat" its way past a neutron?
I learnt here Is a neutron deflected sideways by a laser beam? that a photon beam has no influence on the motion of a free neutron in the first and second approximation. Now I'm interested in what ...
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Tunnel ionisation and how to interpret changes in potential curve
I have been doing some literature review on species ionisation to understand a particular mechanism that occurs when a high-intensity femtosecond laser interacts with molecular nitrogen to produce ...
-1
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1
answer
70
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Does this explanation of wave-particle duality correspond with any existing formal explanation?
Imagine a tsunami wave. Out at sea, it slowly raises the water level not more than a few inches or feet, and passes by standing boats with barely any resultant turbulence. It moves very fast, but it's ...
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How does the current flow in the Hertz expermiment when reverse voltage is applied and the polarity of the electrodes is reversed?
In the Hertz experiment, when light falls on the anode, electrons are emitted and they move towards the cathode and thus flow through the circuit.
However, when reverse voltage is applied and the ...
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27
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How do the forces involved in EMR continue to occilate past emmision of a photon
If electric fields are created by an accelerated charged particle, such as an electron, and magnetic fields are generated by electric fields in motion, what are the individual fields that make up ...
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2
answers
87
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Photons don't wiggle perpendicular to their direction of travel do they?
Every 3D visual explaining a photon shows the photon moving through space (let's say on Z axis), with electric component wiggling up and down on the Y axis, and magnetic component wiggling left and ...
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1
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77
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Photon emission rate frequency dependency
I am puzzling over the dependence of the energy flux of electromagnetic radiation on the frequency of the source.
The power radiated in any direction or solid angle from a charged particle ...
- 1,030
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1
answer
176
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How to understand the Orbital angular momentum of a photon that is not an integer？
How to understand the topological charge that is not an integer, how would the signal OAM crosstalk if one were to model its transport in turbulence, for example, if the beam carries a topological ...
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2
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1k
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Does a running motor generate photons?
Since a motor consists of electric field generated through AC current and a fixed magnetic field (permanent magnets), does it generate photons?
2
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4
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294
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How does an antenna emit photons at a specific frequency if the antenna is made up a specific metal (Al) for example?
My base assumptions...
An antenna emits energy over long distances in the form of photons.
A photon is emitted when an electron changes energy state from higher to lower levels.
A photon's "...
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2
answers
408
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If photons are massless, how are they reflected and blocked by something that has mass? Shouldn't they pass right through any object?
If photons are massless, how do they get reflected, blocked when something comes in its way? Shouldn't the particle just pass right through any object?
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3
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Why does light interact with normal matter but not with other light?
Why does light interact with normal matter but not with other light?
Assumptions:
Light does not interact with other light at all.
Light does interact with other matter, i.e reflection/refraction.
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50
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Left-handed antiphotons in negative-index material?
Do “left-handed” antiphotons propagate in negative-index metamaterials?
https://pubs.aip.org/physicstoday/article/57/6/37/914849/Reversing-Light-With-Negative-RefractionMaterials
Some quotes from the ...
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1
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170
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Why is UV radiation below 200nm strongly absorbed by Oxygen?
According to https://en.wikipedia.org/wiki/Ultraviolet#Subtypes Ultraviolet radiation below $200$ nm is considered to be Vacuum Ultraviolet, due to being strongly absorbed by atmospheric Oxygen.
...
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3
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837
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"Artificially" time dilated photons
If you bang on the table you create a single thump, but if you keep doing so with shorter and shorter intervals, eventually it'll start to sound like a note with a particular pitch.
Now, if I used a ...
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3
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QED photon path (direction of photon emission)
In QED we look at all possible path a photon could go from S to P, and I understand the most significant contributions to the final arrow are the few near straight paths connecting S and P while other ...
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1
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130
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Light wave/photon doppler effect
So I understand the explanation/derivation of doppler effect from the perspective of wave crests emission being stretched out as the source moves. But how does this work from the photon point of view?
...
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2
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587
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Compton scattering with free electron
When the photon is incident on free electron, we say that compton happens. Though, we require that photon is x-ray or gamma ray. I wonder why at least x-ray is required.
I have my own observation and ...
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1
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55
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How to calculate the change of the density of photons in different frames?
I have a problem in getting the transformation of the intensity of light.
1>> Using the transformation of the energy-momentum tensor $T^{ik}$, we can obtain
We have used the fact that $T^{00}=W$...
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2
answers
195
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What happen to the electromagnetic waves when a photon's "wave function" collapses?
We interpret the electron's wave function as a probabilistic wave function. During a measurement, it has the probability to collapse to any of the eigenstates of the measurement operator based on the ...
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2
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152
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Max Planck - what does 'per wavelength' mean?
Planck says
$$B_\nu(T)=\frac{2hc^2}{λ^5}\,\frac{1}{\mathrm{e}^{hc/λk_BT}-1}.$$
It's defined as energy emitted per unit volume per wavelength. I'm not sure if this includes per solid angle, but I ...
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1
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110
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Max Planck - what's the $B$?
Planck says
$$B_\nu(T)=\frac{2\nu^2}{c^2}\,\frac{h\nu}{\mathrm{e}^{h\nu/k_BT}-1}.$$
It is power emitted per unit area per unit angle per unit frequency. This is what I'm curious now.
Let's say we ...
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3
answers
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Photons: Why not wave only? [duplicate]
It seems that Einstein's 1905 paper "Concerning an Heuristic Point of View Toward the Emission and Transformation of Light" notes the discrete quanta of light energy, an idea that leads to ...
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2
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110
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How do scientists focus high energy electromagnetic waves onto a target?
For visible light, we are able to use mirrors to focus on what we want.
However, gamma rays' wavelengths are too short and can't see solid objects.
So how do scientists focus high-energy ...
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0
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46
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Does a plasma with plasma frequency $\omega_p$ generate photons of the same frequency?
I know that photon emission in plasma results in a change of energy level of the electrons from excited or ionised atoms. However, I saw that photons of 13eV were created in a helium plasma, but this ...
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1
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166
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De Broglie wavelength of a photon
The de Broglie wavelength of a photon and the wavelength of its corresponding electromagnetic wave are numerically the same. Is this just a coincidence and the two waves are different or is the de ...
- 128
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3
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132
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Pressure due to a single photon
I'm interested in the pressure exerted on a material when a single photon is absorbed.
I have written the following expression for pressure:
$$
P = \frac{hf}{cA\Delta t},
$$
where $A$ is the area over ...
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