Photon Definition and 1000 Threads

Hi Guys and Gal's In answering a question in general physics I came across the following which explains at a reasonably basic level what a photon is, spontaneous emission etc at the level of basic QM with a bit of math: http://www.physics.usu.edu/torre/3700_Spring_2015/What_is_a_photon.pdf...

Hi there! I wanted to ask you, we know that light, photons have a certain fixed speed generally. Wouldn't this imply, considering Heisenberg's uncertainty principle, that the uncertainty for the speed (momentum) of the photons, should be infinite? But we know for sure, for example, that...

In high energy Z-pinch, lots of X-ray emit. Which direction is the highest density of photon radiation?

When protons, due to their electric charge, interact with photons are the quarks somehow also involved in this same electric interaction? After all, the quarks do have fractional electric charges. Thanks in advance.

Hello Forum, What does the process of two-photon absorption photon entail? That, in general, a molecule or atom (composed of many electrons) that is illuminated by an electromagnetic field can only absorb one photon at a time except in those special cases where two photons can be absorbed...

Photon's rest mass is zero. What's its 'moving' mass? Thanks.

If a accelerated electron 10keV fly through a decelerating electric field that is set by 10KV high voltage, then after exit, the electron all kinetic energy is lost and become 0 velocity. Of course, braking radiation will happen. My question are: 1. what is the direction of radiation photon...

please look at he underligned formula. is it a axiom we have to ake for granted ?

Ok I am no physicist, by any means but a thoughy struck me the otherday. If i where to build a box with a volume of 1 cubic plank length , and the inside of which was a perfect mirror, and i contained within it a photon or multiple photons, how would this affect the speed of light? I believe...

I am trying to better understand the concept of second order coherence G2(τ) (in particular G2(0)) and a few questions have arisen. Note that I am trying to get a physical idea of what is happening so I would appreciate it if your responses can keep the math to the minimum possible. :) How do...

When thinking of sound waves (or more commonly seen waves) the doppler effect is fairly obvious. A car is moving away from you, it's horn's membrane is fluctuating, increasing & reducing air pressure over time. So if it's moving away from you the sound's peak would occur further away...

Hi. In the derivation of the relativistic formula for adding velocities, the Lorentz factor drops out. Mathematically, the formula works for inertial frames with relative velocity c and even gives an answer to Einstein's famous question about what happens if you drive at the speed of light and...

Homework Statement The average wavelength that LED emits is 500nm. The electrical power of the LED is 300mW and the efficiency of turning energy into light is 66%. Number of emitted photons in unit time is? Homework Equations ##E_f=hcf## ##\frac{Pt}{E_f}=number of photons## The Attempt at a...

I have a question that seems to reflect my main concern with QM. Here it is: Consider a series of polarisation-entangled photon pairs that are sent in opposite direction to two measuring devices (e.g. at opposite ends of the universe). The measurement consists of detection of a photon after...

<<Moderator note: Split from thread Photon the smallest particle>> @Orodruin - Let me ask a question. This is an aspect of QFT that has always puzzled me. Suppose we have an RF cavity or a laser cavity with a standing E-M wave. I understand that we can view the field in the cavity as a...

Hi can I ask a question please, is a photon the smallest particle known ? If it is then how do we know there isn't something smaller as the light would blind us from a smaller particle ?.

Hi, I've read some high school "derivations" of ##E=m\cdot c^2## that all considered single photons with momentum ##p=E/c## that are absorbed or emitted from some massive object, changing its mass. So they actually only showed the incremental $$\Delta E=\Delta m\cdot c^2 .$$ Most of those...

Homework Statement I have a question regarding Klauber's Student Friendly Quantum Mechanics, about renormalization in chapters 13 and 15. I have included all relevant equations in the attached document. In equation 15-105 he obtains an expression for the PI_uv(k^2) term used when calculating...

In January 2016, Dr. Attila Krasznahorkay (at the Hungarian Academy of Sciences’s Institute for Nuclear Research in Debrecen, Hungary) and his colleagues published a paper announcing he had found a dark photon by firing protons at lithium-7, which created unstable beryllium-8 nuclei that then...

Hi, Is the energy a photon carries with respect to its frequency the same as that of its momentum energy? My understanding is that it is by the energy relations, $$hf=E$$ $$E^2=p^2c^2+m^2c^4=p^2c^2$$ for a photon with ##m=0##, frequency ##f## and plank constant ##h## . So we have from both...

klotza submitted a new PF Insights post The Interaction of Sound and Light Continue reading the Original PF Insights Post.

Alright, so I'm by no means a trained physicist and most of what I know comes from sporadic readings on the internet, but I had a strange theory the other day. I'm more the type to think in visualizations or analogies rather than cold hard math, so I'll explain it the way the idea came to me...

I know formula ## p=\frac{h}{λ} ## p is photon momentum h is plankc constant λ is EM-wave wavelenght but it is only valid for one wave. How to describe most general EM- field in terms of photons? Is there always discrete number of photons? If EM field is given in terms of a)EM-vectorfield...

Light is an electromagnetic radiation with two wave components that are perpendicular. Between these two perpendicular waves, where is the photon in this system.

So I've heard from multiple sources that one explanation for why light slows down whilst traveling through mediums other than a vacuum is that the light "takes every possible path at the same time" through the medium. Below I've drawn my two possible interpretations of what that means. Can...

Consider a fully entangled pair of polarized photons, A and B, fired at two detectors with polarisation filters in front of them. I have to get a little philosophical to understand the way the interpretations of this experiment play out. My knowledge is still very basic but I'm working on it...

In my education of QM, I've heard countless times how energy is quantized by Planck's Constant, and how radiation is only emitted and absorbed in these discrete steps. Recently I've heard that that's not the full picture of energy, and I was hoping you could draw some clarity for me. In...

Is it possible to build an apparatus that could do the following (at least ideally in principle)? If so, what would it be like? A fairly localized light wave packet (with a corresponding spread in momentum) reaches the origin of our coordinate system from any direction in the XY plane (taking 2...

Just watched many times (specifically @ 20:13 - 25:04) Ron Garret's 'Google Tech Talk' All was going well - the 2 photon experiment & concept visualised - only that the finality of comprehension wasn't delivered... perhaps because Ron was merely using this for his own purpose. This seems a...

Does measuring a polarized photon after it passed a polarization filter put the measurement apparatus in a superposition of detected/not-deteced (the photon)? Does this depend on whether the photon is part of an entangled pair?

If we measure, say, the polarisation of a photon, the polarisation state of the photon collapses along the eigenvector of the observable corresponding to the measurement. This may seem as a loss of information of the original polarisation (for it is now collapsed into another value). However...

Homework Statement Consider Comton scattering of a photon by a moving electron. Before the collision the photon has wave length λ and is moving in the +x direction, and the electron is moving in the -x direction with total energy E. The photon and electron collide head-on. After the collision...

Dear PF Forum, Yesterday (on Sunday) my friend texted me, "the mass of a photon is 10-18 Ev/c2## If my number is correct. And I also I check it in Wiki, and it's true. Now what I want to ask is this first. I Understand, my wording is confusing. Now, I'll rearrange my question for a new question...

I am trying to calculate the Lyman-alpha wavelengths of photons emitted from different hydrogen-like atoms such as deuterium and positive helium ion 4He+, using the relation 1/λ = R*|1/ni^2 - 1/nf^2|, where R is the Rydberg constant and ni and nf are integer numbers corresponding to the initial...

I understand that the photon energies given by the Planck-Einstein relation, though highly precise, are approximations. But have they been confirmed at all experimentally or in practice? If so, across the board or just some of them?

Planck length is ~ 1.6\times 10^{-35} meters. Does this mean that this may be a lower limit on meaningful wavelength and therefore upper limit on energy?

Equation of matter particles are Schrodinger,Klein-Gordon and Dirac equation.But the state of photons can not be represented by positions,then what is quantum equation of a single photon?Also what is the equation of single gluon? (quantum equation means the evolving of the state in time)

Can anyone suggest me a book on quantum electrodynamics for beginners? Thanks in advance

I have a basic question about the trajectory of a photon. As can be seen in the figure above, let's suppose there is a stationary frame F and a cylinder sealed with two sided mirror is located at the origin of F. Then let's consider two cases; First is the velocity of cylinder is 0 with...

Suppose we have a photon fired at a half-silvered mirror. There is a 50% chance that the photon reflects, and a 50% chance it passes through, right? Suppose there are two detectors, one that only detects reflected photons and one that detects only passed photons. So my question is: does the...

The mass of a photon is zero but why does it have a momentum and an energy (E=mc^2=hv) ?

I understand that this determines a probability, but of what exactly for a single photon? The probability that the photon will be detected on a surface where the photon is pumped, e.g. where on the surface the laser is aimed?

My question is about the experiment in which detectors are used behind the slits to determine which slit the photon goes through. Specifically, it's about the detectors themselves. What I found is that these detectors are some kind of photoelectric detectors. My question is this. During the...

A beam of electron in vacuum with velocity v enter a region of spa e with a electric field E. The field is such the electrons circle with radius r. The electrons are now accelerating at constant tangential speed. Because this is not an atomic orbital then by classical physics the electrons...

Although mass-less, a photon, like any other quantum particle, has a frequency/wavelength associated with its energy/momentum. If we have a group of photons all with the same specific energy, then each photon can be represented by a little, complex-valued plane wave. Photons are also EM waves...

I picked up a book titled "Physics in Nuclear Medicine" that, while a slightly outdated edition, will presumably still have a bunch of valid fundamental information inside. One thing I noticed in it talking about EM radiation behaving as packets of energy was that it states: "The energy of the...

Hi! I'm not studying physics and what I know about light is mostly what I've read on the internet and what I've learn thinking and observing the nature. I come to realize that the space is full of light. When I look at the black space, I don't see light but I know that is light everywhere up...

This question has been bugging me quite some time now. I'll start presenting my background for the problem: Fact: Photons are time-dependent oscillations of electric and magnetic fields as described by Maxwell's equations. Now, I've heard a lot of people, including professors saying that a...

I don't know where I'm going wrong with this problem - I was so sure I had it right but the online grader tells me otherwise :oldfrown: Homework Statement An electron in a one-dimensional box has ground-state energy 2.60 eV. What is the wavelength of the photon absorbed when the electron...

Hi everyone, Anybody knows if the photon energy (frequency * Planck's constant) can be derived from more basic physical principles or this formula was "invented" to explain the photo-electric effect or black body radiation? If you know a way to derive it, please share. Thanks a lot !