Questions tagged [photons]

The photon is the quantum of the electromagnetic four-potential, and therefore the massless bosonic particle associated with the electromagnetic force, commonly also called the "particle of light". Use this tag for questions about the quantum-mechanical understanding of light and/or electromagnetic interactions.

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Emissions from a Blackbody and the UV Catastrophe

Recently I found myself becoming confused over a topic that I thought I had previously understood. In a theoretical blackbody which reaches thermal equilibrium the energy absorbed is equal to the ...
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How do photons get into the eyes?

I hope you will understand me correctly because there are some things that I translated. It is known that we see the world around us thanks to photons that are reflected from the surfaces of objects, ...
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Photons - difference

Is there a difference between an observed photon from the sun and an observed photon from the sun that has bounced off the moon? Is there a difference between an observed photon from the sun and an ...
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Are photons absorbed during photolysis?

When photolysis occurs, for example photolysis of an oxygen molecule occurs to form two separate oxygen atoms, is the photon that started the reaction absorbed to provide the energy needed for the ...
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63 views

Direction of emission of Photoelectrons [duplicate]

Where does the information about the direction of the emission of the Photoelectron come from? Does it get it from the incoming Photon? I have seen a picture on wikipedia-page of the photoelectric ...
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Why isn't the chemical potential of photons equal to $\hbar\omega$

I am confused about the chemical of photons. Specifically, I don't understand what's faulty with the following derivation: Consider a black body at equilibrium temperature $T$, and let's focus on a ...
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Is light propagation being slowed down at the media interface?

Read the article and watch the video here: https://phys.org/news/2019-05-ultra-fast-imaging-technology-high.html. If you click the video (especially the second one), it seems that the light was slowed ...
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Dark Matter Wave Particle Duality

CERN is looking for dark photons, and they are seeking to look for interactions with the Higgs boson with the dark photon.See link here. So in other words a dark photon - a mediator for dark matter is ...
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Can a wire having a $610$-$670$ THz (frequency of blue light) AC frequency supply, generate blue light?

We know that when we give alternating current across a wire then it will generate an electromagnetic wave which propagates outward. But if we have a supply which can generate 610 to 670 terahertz of ...
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Single photon interference, state “top” current theory [duplicate]

Is there a simple generally accepted explanation for single photon interference? Does each photon interact with or see both slits?
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What happens to photons that have enough energy to form a Black Hole come together at a point in spacetime?

This answer to a question posed a few days ago made me wonder. I made this comment to the answer: So if we place (as dense as possible) high power lasers on a sphere with a radius of, say, one ...
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Is the electric field arrangement in photon fixed? [closed]

When we measure a photon's electric field (let's take a visible light photon) then do we observe the electric field's direction first, let's say, upwards then downwards? Or is the detection of both ...
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What happens if matter particle and antimatter particle both carry no charge were to collide elastically?

I read that particle carrying charge is able to interact with photon so that when electron and positron collides they may be converted into pure photons, then what about neutron-antineutron collision? ...
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Disagreement about solving density of orbital per unit energy of photon gas in a cavity

A conducting 2-D cavity (of area $L^2$) contains a photon gas that satisfies the dispersion relationship: $$\omega^2 =\frac{4\pi^2c^2}{L^2}(n_x^2+n_y^2)$$ and I wish to find the density of the ...
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Why is photon quantized in vacuum? [duplicate]

Apparition of quantized energy levels in quantum physics is usually explained in analogy with sound waves in a box (like in music instruments): the wave has to satisfy the boundary conditions and ...
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Why does decreasing the wavelength of light while maintaining intensity decrease current in photo electric effect [duplicate]

I understand a photon with a smaller wavelength is more energetic so for a given intensity, less photons are incident on the electrons and so less photo electrons reach the detector per second. ...
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Question about pair production

Pair production can't occur in vaccum because momentum cannot be conserved because the photon does not have a rest frame of reference, that means that the produced pair has a center of mass frame of ...
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Is acceleration of particle by photon a continuous process?

There are a lot of questions, so I assigned a number to each one. Let's assume we have electron which is not moving in some inertial frame of reference. Let this electron be hit by a photon. Since ...
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Pair production problem, how is energy not conserved here?

The problem is asking me to find the minimum photon energy that would produce an electron-positron pair when it collides with a free electron at rest. This is my attempt at trying to conserve both ...
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How do photons encode images?

When light bounces off an object, the light then travels into the eye of an observer who can then reconstruct the image. Do the photons encode the image and how do they do so?
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Do photons bend spacetime or not?

I have read this question: Electromagnetic gravity where Safesphere says in a comment: Actually, photons themselves don't bend spacetime. Intuitively, this is because photons can't emit ...
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What happens if I replace an IR laser diode with CD burner laser diode in green laser pointer [closed]

I was wondering what happens if CD burner photons hit the crystal NdYO4 and KTP 780 nm wave length where original 808 nm IR pumper diode. I am confused with NdYO4 crystal I know that KTP is a ...
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Why is the photon emitted from a bound electron dropping energy levels not exactly equal to the difference in energy levels [duplicate]

In a problem sheet there was a question asking us to guess why a photon released from an electron dropping energy levels does not have the exact difference. My guess is that the electron needs some ...
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Is it possible to manipulate the polarization of unpolarized light within a medium via Electric field?

You see this setup above. There is an unpolarized light source travelling through a transparent dielectric medium. Think of this triangular shaped medium as a capacitor. there are 3 conductive sides ...
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Photons and electromagnetic waves

If an electromagnetic wave is constituted by a continually accelerating charge, then how can a photon be neutral?
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Is the Compton effect observed during regular x-ray diffraction?

Here we have the standard set up to observe the compton effect. From what I understand, due to the particle like nature of light, when the x ray photons collide with the electrons in the scatterer ...
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What experiment would confirm De Broglie equation on photons?

If we want to check experimentally that, for a photon: λ=h/p (De Broglie equation) Has such experiment been carried out? What is/would be the experimental setup? Wikipedia doesnt show such protocol ...
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Four-velocity vector of light

Please note that my question is not a duplicate, it is not about the speed of light, my question is only technical about the four velocity vector for light, its definedeness, value and constantness. ...
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How do electrons ever receive the amount of energy needed to move up energy levels?

Suppose there is a (blackbody) electromagnetic radiation source. It should emit a finite amount of photons every second with an intensity against frequency graph looking similar to a Maxwell Boltzmann ...
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Does optical density depend upon concentration of a solution?

Does optical density vary upon the amount of salts dissolved in water?
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Why can't we have a massive photon in the Standard Model of Particle Physics

I've heard that in the Standard Model of Particle Physics you can´t have a massive photon whatever you do but I'm having a few problems showing that. I understand that the trick to make this work is ...
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How do I measure the (near) infra-red radiation intensity?

I need to measure how much of the radiation is absorbed by a specific fabric (as in "what percentage of photons is absorbed"). I am interested in 2 LEDs: 650nm (red) and 800nm (infra-red). The ...
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Can Compton scattering increase a photon's energy?

I've read (in Hagai Netzer's book The Physics and Evolution of Active Galactic Nuclei) that "Comptonization in the [black hole's accretion] disk atmosphere can increase the energy of some photons..." [...
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Would an observer going faster than the speed of light in a vacuum be able to observe photons that they emit? [closed]

If I could exceed the speed of light in a vacuum, would I be able to see photons that I previously emitted? Would this be theoretically possible?
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Spatial wave-function of a single photon and its measurement

In the last decade there were several papers claiming that they've measured a "transverse quantum state" / "quantum wave-function" / "spatial Wigner function" of a single photon: Measurement of the ...
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In what sense do photons exist?

In a photon's frame of reference travel is instantaneous, so presumably a photon cannot exist in its own frame of reference. I am not aware that a "beam" of photons interacts via gravity despite ...
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Why can we parameterize a null geodesic such that its velocity is four-momentum? [duplicate]

One principle in general relativity is that the wordlines of massless particles are null geodesics. It also seem to be a commonly stated fact (for instance see eq. (3.62) in Section 3.4 of Carroll's ...
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Photons’ Speed (light speed) in vacuum [duplicate]

In a vacuum, are photons always traveling at 100% light speed? Can photons go any slower in a vacuum? They have no mass which means they can go at 100% light speed, but do they have to?
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Why do we assume the photon has lost all its energy to the electron in the photo electric effect but not the Compton effect?

I was just revising the Compton effect for my exam and was wondering why in the case of the Compton effect we consider the photon as having collided with the electrons and only partially losing its ...
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1answer
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Black hole gravity and light [duplicate]

When an object is squeezed to its Schwarzschild radius it becomes a black hole (made by density) and its mass does not change (its gravity doesn’t change), but if its mass doesn’t change (its gravity ...
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Quantum mechanics of refraction and reflection? [duplicate]

I learnt that light bends when passing through different mediums is due to the epsilon which is how much the strength of electric and magnetic field in the direction of travel changes in the material, ...
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When do we need fully quantum mechanically treatment of photon?

I'm wondering when do we need fully quantum mechanically treatment of photon.(i.e. quantized photon and quantum matter.) I kind of know that for sub-Poisson(photon statistics) light, fully quantum ...
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Question about field quantization

I'm reading a paper by Rubin, Klyshko, Shih and Sergienko titled "Theory of two-photon entanglement in type_II optical parametric down-conversion", 1994 (link to the paper). I'm stumped by equation ...
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When an electron around an atom drops to a lower state, is 100% of the energy converted to a photon?

Let's say we have an electron around atom. Let's say the electron drops into a lower electron shell. Is 100% of the energy difference converted to a photon? Does the atom recoil at all? Is the any of ...
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1answer
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Question about Homodyne detection

In this Review of modern physics, section "II. A.", optical homodyne detection is briefly reviewed. In equation (9), it is stated that the fields after the beam splitter are $$E_{1}=\frac{E_\text{L}+...
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Atomic model - absorption [duplicate]

I have a question regarding the absorption of light in e.g. hydrogen atoms: I didn't quite understand how the electron knows that it can only absorb photons of the right energy. I thought that when ...
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Are photons “born” travelling at the speed of light? In what manner do they propagate through space? [closed]

When an electron jumps from a high to a lower energy level and a photon is created, can the photon be detected from all vantage points or only from a discrete position? Does the atom nucleus cast a ...
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Why is the magnitude of a photons 4 momentum vector 0 if it has momentum?

I've just started studying 4 vectors. I understand because a photon has 0 rest mass and travels at c, you can not define a 4 velocity for it, and as momentum 4 vector = mass x velocity 4 vector, it ...
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How does the electron know to “release” the photon at the same angle at which it got absorbed? [duplicate]

This is a quote from Wikipedia: In classical electrodynamics, light is considered as an electromagnetic wave, which is described by Maxwell's equations. Light waves incident on a material induce ...
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What happens after barium sulphate absorbs gamma rays?

BaSO4 will happily absorb gamma-rays, presumably bumping electrons up into outer orbitals. What happens next? I assume fluoresence as electrons drop back. Will the BaSO4 be safe to handle immediately ...