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 ...

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Electron-positron annihilation [duplicate]

Photon pair production in electron-positron annihilation is necessary to conserve the linear momentum. In such discussions the electron-positron pair collide with equal and opposite momentum, if they ...
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Effects of gravity on light on the surface of the Earth [closed]

I read over the question and answers on the effects of gravity on light. I would like to ask a more specific question about gravity and light. What is the effect of gravity on light on the surface ...
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1answer
58 views

How do you detect a photon without consuming it?

In double slit experiment, they say they can put a detector after the slit so they know exactly which slit the photon has passed. But if you successfully detect a photon, isn't the photon also ...
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1answer
55 views

By what mechanism is a photon emitted or absorbed in atomic electron state transitions?

I understand atomic emission and absorption spectra well - photons of a specific energy can be emitted or absorbed by atoms, if that energy corresponds perfectly to the energy difference between two ...
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90 views

Can photons be seen with naked eye? [closed]

Whenever I observe the light very carefully I observe many tiny circles of light . I guess these're photons .I'm I right ? If these were photons then it means that they are relatively larger then ...
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0answers
20 views

Is photon massless? [duplicate]

if photon is massless then in E2=m2c4+p2c2 is m=0 ? and p=mv1-mv2 shouldnt be zero too. if both the statements are true then does photon has no energy?
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What determines the sharpness of a shadow?

What are the factors that affect the sharpness of a shadow? I would think that the distance between the light source and the object, the distance between the object and the shadow, and the size of ...
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3answers
42 views

Can light from the same source interfere with itself without utilizing n-slit screens?

I was wondering - can a source produce light which travels in such a configuration that part of it travels a longer distance (i.e., is out of phase with its other part) thus exhibiting an interference ...
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1answer
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Annihilation process and photons [closed]

Why should two photons produced by the annihilation process move in opposite direction? I know you would say for the conservation of momentum but why can't they move in the same direction, I want to ...
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4answers
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Free electron can't absorb a photon [duplicate]

Why can't a free electron absorb a photon? But a one attached to an atom can.. Can you explain to me logically and by easy equations? Thank you..
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1answer
61 views

What is the trajectory of a photon moving through a vacuum?

Since electromagnetic energy is carried by photons and moves in forms of waves, does it mean that a single photon when propagating through space doesn't follow the straight path but instead always ...
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0answers
26 views

Single Photon Counting Module [closed]

I have a single photon counting module from Picoquant (tau-SPAD) . When it is powered on, the TTL output has a constant value of around 4 volts (as opposed to occasional TTL spikes indicating photon ...
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3answers
89 views

Energy in one wavelength

I know that the energy of one photon equals $E=hf$ and that concept of photons came from the photoelectric effect. My question here can we assume that a photon equals one wavelength for example if we ...
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Do light particles come in different sizes? [duplicate]

Do light particles come in different sizes if it makes sense to even think about them that way?
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184 views

How in detail the rotation of the electric field component of light during transition through a polarizer takes place?

I ask "After a slit, are photons polarized?" and later found two answers for the question "Why does the electric field dominate in light?". From this two answers I have concluded or summarized, that ...
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1answer
22 views

Radiation weighting factor photons

I'm wondering about the equivalent dose and the radiation weighting factor of photons (according to ICRP 103). Why is the weighting factor independent from the energy of the photons?
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3answers
188 views

If mass is not conserved but instead energy is conserved, is it right to say that the fundamental particles are photons? [closed]

If mass is not conserved but instead energy is conserved, so is it right to say that the fundamental particle of the Universe is photon instead of protons, neutrons, electrons, leptons, etc and all ...
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2answers
89 views

Does the attached figure show how particles produce wave?

I have always been trying to understand and visualize what wave is and how it's been produced. I guess what ordinary people know about wave is just a particle moving up and down but last week I came ...
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0answers
32 views

Nature of Particle waves [closed]

My question relates to the properties of a single particle (for example purposes lets use a photon) Forgive me if this subject has already been answered by science, i am not aware that it has been ...
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0answers
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How can I estimate the number of X-Ray photons generated from a x ray tube?

I have this problem. I have an x ray tube of which I know the specific (kV, mA, anode material) and I have to estimate the number of X ray photons hitting the sensor after passing through air and ...
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4answers
74 views

If a silver atom scatters light isotropically, what happens if only a single photon is scattered?

From this question :Why is the light reflected at the same angle from mirror? and this part of the answer: The starting point it that a single silver atom is far smaller than the wavelength of light, ...
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3answers
70 views

Can a single photon be elliptically polarised?

Can a single photon be elliptically polarised ? or is elliptically polarised EM-radiation a mixture of circular and linear polarised ?
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1answer
25 views

Photon absorption and Sight [closed]

If light is made by emitting photons and photons are absorbed by our eyes to see light then i have this question: if there is one person in the room and he looks at a light source (L) with x photons ...
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1answer
88 views

Application of Heisenberg's uncertainty principle on photons

While I was hobby-reading about quantum mechanics I came across Heisenberg's theory. But while I was trying to understand it I thought of this: if the speed of light (as well as the momentum of a ...
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1answer
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Do photon inside event horizon exceeds speed of light?

Event horizon is a region of space whereby nothing with information can escape, so I imagine that a photon falls into this region of space does it accelerates toward the singularity if it exists? Do ...
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Photo's vector characteristic

In Frank Close's infinity puzzle, it says that to maintain the invariance for electric charge requires some means to transmit information about the local charge of gauge to electric charges elsewhere. ...
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3answers
105 views

About quantization of EM energy for amplitude-modulated wave

Consider an electromagnetic monochromatic plane wave at frequency $f$ and E-field amplitude $E_0$ in vacuum. From the quantum electrodynamics point of view, we could say that the energy that EM wave ...
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3answers
373 views

Can an electron gain energy by another electron?

Is it possible for an electron to gain energy from another electron which is jumping from higher energy level to lower energy level, and shifts to higher energy level?
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1answer
71 views

What is the physical nature of electromagnetic waves?

I've been trying to work out what the physical nature of electromagnetic waves is, since I reasoned that given electromagnetic waves have wavelengths that are given in distance units, rather than ...
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2answers
74 views

After a slit, are photons polarized?

It seems clear that a photon stream as well as single photons behind a well designed slit - the right slit width for a given wavelength - are polarized. Means, the electric fields of such photons are ...
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1answer
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Can we accelerate photons to travel at speed of $1.5c$? Or any $xc$ when $x > 1$? [closed]

Can we move photons to travel at speed greater than speed of light in vacuum? If no then why? For example: I want to send some photons at 1.5c. Is that possible? How a photon of light can go from 0 ...
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Photon absorption and emission in 2nd quantization

I am looking for models which describe the interaction of matter (lets take a 1D chain of atoms) with photons, especially the emission and absorption. I would love to see the derivation of models in ...
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2answers
90 views

Why does number of photons fluctuate?

When counting photons (with, e.g., a CCD), there is the so-called ''photon noise'' (important at low photon numbers). What is the explanation in the framework of QED, QFT? Is it the Heisenberg ...
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0answers
17 views

Concerning Thomson scattering

In https://en.wikipedia.org/wiki/Thomson_scattering, the intensity of the scattered light is diminished by the factor $\cos^2(χ)$. Can this angular dependence also be derived with quantum mechanics ...
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2answers
62 views

Can light have zero wavelength?

As you increase the energy of a photon it's wavelength shortens. Is it theoretically posible for light to not have a wavelength? Like a still pond?
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Compton effect in photo-electric?

In photo-electric effect Einstein said that photons incidents on material and gives their energy which will gives kinetic energy to electrons. But i also want to know that why Compton's effect not ...
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2answers
73 views

Why does the critical angle for refraction exist?

When light moves from a medium with a high refraction index to a medium with a low refractory index (water to vacuum), that there exists a "critical angle" at which no more refraction occurs. What is ...
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69 views

how to analyze the collision of two photons with four-momentum vector? [closed]

Q: If two photons with energies $E_1$ and $E_2$ collide, with their trajectories making an angle $\theta$. Is the following right about individual initial 4-momentums and total initial 4-momentum? and ...
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1answer
35 views

Accelerating electric charge

We know that massive bodies attract gas clouds that become ionized and the resulting acceleration can emit very high energy photons. In a case where a proton for example is undergoing prolonged ...
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Photon behaviour [duplicate]

What happens when a photon hits a mirror? Does the photon decelerate instantaneously to zero and then accelerates instantaneously to the velocity of light when it is reflected from the mirror? How do ...
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2answers
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How can photons cause charges to attract? [duplicate]

Photons are the force carrier of the electromagnetic force. I do not see how this could result in a transfer of momentum that attracts objects together. I am primarily interested in an intuitive ...
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1answer
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If photons have mass then how can they travel at speed of light? [closed]

Anything that has mass must be slower than speed of light. If they are travelling at speed of light they must contain infinite energy which should be able to destroy everything, clearly thats not ...
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0answers
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Will the flash light accelerate in space? [duplicate]

As we know from school physics course light has pressure. So my question is will flash light accelerate in space in the direction opposite to light emission? If not, then will flash light with ...
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1answer
52 views

Difference between photon upconversion and two photon absorption?

One can find in the wikipedia the following assertion: Upconversion should be distinguished from two-photon absorption However, it is difficult to tell the difference between both processes by ...
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3answers
49 views

Interference of two identical laser source

Do two identical but separate laser sources cancel out each other when point on the same spot? By the way both light will be coming from same direction. And of course, they will have a phase ...
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0answers
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In a photovoltaic effect, when the electron absorbes the photon, is the electron's energy displaced?

I'm a super amateur wannabe physicist, and I'm trying to learn the fundamental workings of the photovoltaic effect. I haven't been able to understand "how" or "what" is displaced/transmitted in the ...
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1answer
58 views

Help me understand Pound and Rebka's experiment

I am a second year undergrad physics student and up until now have done some classical mechanics and some electrodynamics. For some reason I have always been really interested in light. A couple of ...
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Is it possible to select a single carrier type in a photodiode?

I have been reading about avalanche photodiodes and understand that they work via the impact ionization process to produce internal gain in the diode before the signal is read. It appears that ...
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0answers
17 views

Directional propagator for Gaussian single photon emitters

I am generating photons along a vertical line in 2D space (say along the x=0 line) at spatial coordinates $x = (x_1, x_2, ..., x_n)$ by the following means $\hat{a}^\dagger(x_1)\hat{a}^\dagger(x_2) ...
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21 views

Radiative transfer in a two dimensional slab

I am trying to implement some radiative transfer to a hydrodynamics code. However, all texts that deal with multidimensional radiative transfer assume spherical coordinates, however the hydro code is ...