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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Photon - gas molecule collision and conservation of energy?

I thought up a scenario and I'm having trouble working it out. Imagine a single greenhouse gas molecule with it's direction towards the ground. And a single photon leaving the ground hitting the ...
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Energy conservation in reflection of light from a perfect mirror

So I came across a question where a light source is shined on a mirror attached to a spring which is attached to a rigid support. Now, in the solution the question has been solved by equating the ...
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What exactly is meant by the wavelength of a photon?

I've been thinking about this for quite some time, and from looking online I haven't found a satisfying answer. Lots of photons, such as visible-light photons have very small wavelength (which from ...
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Why is the state equation of a circularly polarised photon as such?

$\newcommand{\bra}[1]{\left< #1 \right|} \newcommand{\ket}[1]{\left| #1 \right>}\renewcommand{\vec}{\boldsymbol}$This question can be regarded as a follow up of this question. In this lecture ...
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Frequency plot with photoelectric current and anode potential

Keep your eyes near 0V anode potential - here you can see that the light with maximum frequency has more photoelectric current and that the light with minimum frequency has less photoelectric current ...
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Properties of the photon: Electric and Magnetic field components

Consider an electromagnetic wave of frequency $\nu$ interacting with a stationary charge placed at point $x$. My question concerns the consistency of two equally valid quantum-mechanical descriptions ...
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Does photon electromagnetic field “shake” charged particles and atoms?

Lets theoreticaly imagine completly stationary particle,like electron for example.Can photon,or photons shake it,or oscillate its position? By that I dont necesarily mean the center position must ...
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Is the wobbly rope depiction of a radio wave inherently wrong? And how do vectors of parallel waves align with each other?

I don't have a scientific education, yet I'm scientifically curious. Among other things, I'm struggling to understand the nature of electromagnetic waves. What I have recently realized is that the ...
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How is magnetic flux viewed in QED?

I know that QED is formulated in terms of Lagrangian density. So when we solve for a physical system we ultimately ends up finding $\psi$ and $A_{\mu}$. I'm not interested in $\psi$ for now. Since I ...
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What is the connection between the Poynting vector (EM transverse wave) and the description of photons with $E=h*f$ and $c=f*\lambda$?

I think for radio antenna transmitters, if the AC current's frequency is at the frequency of radiowaves, EM waves in the radio frequency will be emitted? Then the frequency has something to do with ...
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Would the nightsky be bright (filled with starlight) without accelerating space expansion?

As I currently understand, if a photon was emitted from a far away point in the Universe, beyond the event/particle horizon, so that the space inbetween the emitter and us is expanding faster then ...
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Does light have gravity or Gravitomagnetism?

We all agree that light has no mass yet it is affected by gravity. According to accepted theories I have seen light itself is also said to bend space meaning that it causes gravitation. This would ...
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Is the photon velocity regarding a point in a expanding universe constant?

Could be a photon moving in an expanding universe be thought of as an ant moving along an elastic rope fixed at the upper end on a cieling that is streching due to a constant mass at its bottom end. ...
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In double slit experiment, It's the wave function who represent particles, travelling?

I saw some videos that tend to show traveling waves to represent the photon/electron in a double slit experiment. Is it right? Because the space between the electron gun and the screen where these ...
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Why cannot we see back of our head? [duplicate]

Suppose we are watching a star at night, we are able to see that star because the photons from that star reach our eyes, now since the photons emitted by that star will reach earth and if we ...
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Why can't a gas of photons reach a Bose-Einstein condensate?

I have read in many places that as the gas of photons has a chemical potential $\mu=0$ it can't reach a Bose-Einstein condensate (BEC), but I don't understand why. I am reading Greiner's "...
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In diffraction When wavelength is less than slit width then does the scattered light gets absorbed & emitted from the wall or just rebound?

I know that when the slit width is less than that of wavelength then the slit will act as a point source and scatter the light in all directions. But my question is that during the scattering of ...
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What is the most common photon wavelength in our observable universe (not including the Sun)?

Ignoring the Sun, what is the most common wavelength of a photon that is received by us on average? (I am not asking what is the average wavelength, but rather what is the most common wavelength ...
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Plus and minus in the four bell states [closed]

I'm currently working on a project about Bell's inequality and have done an experiment using photons to debunk the hidden variable theory. However, I'm having trouble understanding the four Bell ...
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Electrons emitting photons. Real life example?

In highschool we are taught about Bohr's atom model and how electrons emit light/ photons when transitioning from a higher energy orbit to a lower energy orbit. First question Where does this ...
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Entanglement thought experiment with redshift

Thought experiment: 2 entangled photons, one escape from galaxy to galaxy without hitting an electron and another one got caught between 2 perfect mirrors. Would the redshift (wavelength becomes ...
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Does photon has wavelength or energy corresponding to it has wavelength?

We know that c/lambda is frequency of photon. Now, my question is, we are considering photon as a particle, so how come it has wavelength which is the characteristic property of wave? Here,Light is ...
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Can emission and absorption be separated lightlike, spacelike, timelike?

I have read this question, where I take the definition of spacelike, lightlike and timelike from: What spacelike, timelike and lightlike spacetime interval really mean? Now in this question, Willo's ...
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Why is the force exerted by a light beam on a spherical object independent of the amount of light reflected or absorbed?

When a sphere of radius $r$ is placed in the path of a parallel beam of light of intensity $I$, the force exerted by the beam on the sphere is given by: $$F=\frac{\pi r^2 I}{c}$$ I derived the ...
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How does amplitude affect photon's intensity as a particle?

Considering the scenario were a photon acts as a particle, how does amplitude affect the photon? Does it increase its intensity? How do you visualise this?
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Unnecessary constraint in quantum statistics

In deriving Bose-Einstein or Fermi-Dirac distribution, if $N_n$ is no. of entities with energy $E_n$, then two the constraints for a system with N particles and total energy E are: $\sum_{n=1}^{\...
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Conduction band energy level under illumination

I am new to the field and my apologies if its trivial question. Consider a semiconductor having valence and conduction band at certain energy level. When it is illuminated with photons having ...
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If a fluorescent atom absorbs UV and emits visible light, then how is energy conserved?

Light has a lower frequency than UV, so unless energy is also released in other forms, how can energy be conserved? What other forms is energy released as for fluorescence?
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How do we know not all photons are absorbed? Only those of specific energies?

When a photon hits an electron in an atom, its energy has to be equal to the difference in energy between the current shell and a shell with a higher energy level, otherwise it is not absorbed at all. ...
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In double-slit experiments, path detection makes interference fringes disappear. How comes the detection screen does not?

One observes that the fact of detecting the location of a particle path (which slit the particle went through) entails a collapse of the particle field (interference fringes disappear on the detection ...
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What effect does amplitude have on EM waves?

There have been previous questions like this regarding light/photons specifically. My question is what the effect of the amplitude is on, say, a gamma wave? It would change its energy, as $E = h f$. ...
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Single photon interferometry

I am always surprised by the subtleties that are embedded in the wave/particle dualism. That is why I read again and again the paragraph in the Dirac's classical text dealing with the single photon ...
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Should light travelling post-double slit between an elongated single slit formed from two razor blades still interfere?

I am continuing to experiment with Young's double slit experiment at home. As before I have used a small pen laser and shone the light through double slits formed from very fine wire and black masking ...
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How do the electrons absorb energy in an discharge tube that is used for produce an emission spectrum?

When there's hydrogen in a discharged tube it produces an emission spectrum, emitting energy(photons). (Eg:-When an electron jumps from 3rd energy level to 1st energy level, the electron emits a ...
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What is the origin of optical force?

In photoelectric effect a photon transfers its energy to an electron. Thus it does some work on an electron and work is always done via some force which in this case called optical force. I want to ...
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Pair production mass

I’ve read other questions on here, but I still don’t have the answer that I need. In pair production, where does the mass come from that’s found in the electron-positron pair? I’m extremely novice and ...
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What is the origin of photons in supernova explosion?

How and where (the ejecta or the core) are the photons (that we are receiving on earth) are produced in supernova explosions? What I understand is that the kinetic energy is converted to thermal ...
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The photon traveling at the speed of light [duplicate]

As other people have posted as answers time and distance distortion according to relativity and the Lorentz equations does mean that there is no time and no distance which would infer that sine we are ...
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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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Intuition of spin of photon [closed]

I read that intrinsic spin is a quantum property aka just a number, charged particle such as electron has magnetic dipole moment which can be detected using magnetic field like the Stern–Gerlach ...
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Magnetism and Photons

Knowing that magnetic field is made from photons. Where does a magnet gets it's photons from to create a magnetic field. Are the photons created within the magnet, or does the magnet capture photons ...
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Photons, Gravity and Higgs field [closed]

(a) A photon's path bends towards a large mass, so we say it has gravitational attraction (or that the large mass bends spacetime so that the photon's path curves towards it). But if the photon feels ...
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How can an electromagnetic wave behave as a particle?

Light is an electromagnetic wave and it possess both properties of a particle and wave. Looking at the image I can imagine how it behaves like a wave. However, I'm not sure how it can behave like ...
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What is zero-order transmission spectrum?

In the paper The extraordinary optical transmission through subwavelength hole arrays by T. W. Ebbesen it is shown at particular wavelength there is a peak observed in zero order transmission spectrum....
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How do you get max kinetic energy from photons hitting electrons?

I read if you increase the frequency then you can get the max kinetic energy and if you decrease the wavelengths you can get enough energy to knock the electron out of its atom of a gas. Is this true? ...
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Can a photon be frozen (relatively stationary) in space? [closed]

There are a lot of questions on this site about photon speed, none of them answer my question: Why and how is the speed of light in vacuum constant, i.e., independent of reference frame? If ...
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Multiple observers watching a light source

Every time I think I understand something about QED some very basic things just trip me up again. So, I realise a photon can be thought of as an observation that carries two parameters, its wave ...
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Why doesn't Rayleigh scattering happen at low altitude in air?

An answer I found online was: At high altitude where molecules are far apart, scattered photons can travel without interfering with each other, thus they fill the sky with blue light. But at low ...
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What is the connection between the Planck-Einstein Relationship and the Average Intensity of an electromagnetic wave?

This is probably a silly question, and likely reflects a poor understanding, in general, of electromagnetic radiation, but here goes anyway: I have encountered two equations that I am struggling to ...
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How do materials absorb light?

I've seen a lot of different different answers online so I just want a clarification. Electrons can absorb photons in 2 ways. The first way involves the electron cloud oscillating with the photon but ...

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