Photons are electromagnetic waves. They exhibit particle-like qualities in many situations and have zero rest mass.
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If time stops at the speed of light is a photon 'everywhere' at once? [duplicate]
I am not a physicist so excuse my question if it's paticularly stupid. As a particle gets closer to the speed of light time slows down as for that particle as compared to a reference from the ...
4
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2answers
126 views
Why is the photon emitted in the same direction as incoming radiation in Laser?
When an atom “lases” it always gives up its energy in the same direction and phase as the incoming light. Why does this happen? How can this be explained?
How does the photon generated because of ...
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55 views
Magnitude of a photon?
I encountered the following sentence in my textbook, which I don't quite understand, and after an unfruitful google search, I still can't figure out what they mean by magnitude in this context:
...
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0answers
13 views
How does optical phase modulation produce photons with different frequencies?
The classical description of electro-optic modulators is an index of refraction that depends on the applied voltage. For example, for a sine modulation $\sin(\Omega t)$, a monochromatic laser of ...
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1answer
55 views
Why is the Heisenberg Uncertainty Principle not obvious give the conservation of mass- energy?
A photons energy is given by $E=h *f$ and momentum $p=E/c$ (spin?) but the photon has no (rest) mass! Therefore it is the ultimate probing tool for looking at any mass position and velocity because ...
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1answer
29 views
Can we build a synthetic event horizon?
If we imagine ourselves to be a civilization capable of manipulating very heavy masses in arbitrary spatial and momentum configurations (because we have access to large amounts of motive force, for ...
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1answer
43 views
How do particles become entangled?
A person asked me this and I'm just a lowly physical chemist.
I used a classical analogy (how good or bad is this and how to fix?)
Basically, light has a net angular momentum of zero, insofar as ...
4
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1answer
102 views
Mass gap for photons
I am puzzled by the answers to the question:
What is a mass gap?
There, Ron Maimon's answer gives a clear-cut definition, which I suppose applies to any quantum field theory with Hamiltonian $H$, ...
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0answers
34 views
Contact electricity and photoelectric effect
Most universities provide an experiment about the photoelectric effect to determine $h$ by measuring the stop voltage against the light frequency and calculating the slope $h/e$.
But mostly they also ...
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5answers
3k views
Why doesn't light kill me?
I was attending my philosophy class and in the middle of student presentations, I found myself mentally wondering off and thinking about light. After a few minutes of trying to piece together how the ...
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0answers
20 views
Does quantum mechanics depend solely on electromagnetic waves? [duplicate]
I am beginning to learn quantum mechanics. Since determining the position of an object involves probing by electromagnetic waves and since i have read a simple derivation of Heisenberg's uncertainty ...
4
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3answers
117 views
Precision of Coulomb's law
Up to which precision has the coulomb law proven to be true?
I.e. if you have two electrons in a vacuum chamber, 5 meters appart, have the third order terms been ruled out? Are there any theoretical ...
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1answer
75 views
How can we detect X-rays?
I know that X-rays can be detected by various ways, like ionizing of air particles.
Is there a way to detect X-rays,which are photons, by detecting ? Can something absorb the energy of the X-rays and ...
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1answer
94 views
Photons, where do they come from? [closed]
Photons, where do they come from?
What exactly is a photon?
I've certainly heard how they get produced, but it doesn't seem to make sense that some sort of particle should need to be produced just ...
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1answer
50 views
Is the de Broglie wavelength of a photon equal to the EM wavelength of the radiation?
Is the de Broglie (matter) wavelength $\lambda=\frac{h}{p}$ of a photon equal to the electromagnetic wavelength of the radiation?
I guess yes, but how come that photons have both a matter wave and an ...
2
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1answer
67 views
Difference between electromagnetic radiation (EMR) and Electromagnetic Field?
I'm a freshly graduated electrical engineer. One course that I really struggled with was Field Theory, because it was a lovely assortment of vector calculus and things that were explained to me well ...
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1answer
116 views
Why does Lorentz factor not hold for relativistic mass when we apply it to photons? [duplicate]
We know that the photon itself is massless particle $m_0=0$. But we also know, that the mass of the objects does increase with their energy. And we know that under certain circumstances (gravity, ...
2
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1answer
57 views
In solar cells, do photons break apart electron-hole pairs, or create them?
Some sources say that when a photon hits the PV cell, it breaks apart electron-hole pairs. Other sources say that photons create electron-hole pairs. Can anyone explain which one is right? I've read ...
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0answers
23 views
Energy needed to raise energy level of an atom? [duplicate]
Suppose I have an atom at rest which is at energy level $E_i$. Would it be possible to raise it to the next higher level $E_{i+1}$ by shooting a photon of energy $E_{i+1}-E_i$ at it?
I ask because ...
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1answer
59 views
Where is the amplitude of electromagnetic waves in the equation of energy of e/m waves?
Does the amplitude of the photon oscillations always stay constant and if it is not - what are the physical differences between the photon with higher amplitude in comparison to the one with the less ...
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1answer
47 views
EM Waves Energy Loss
Where does the energy go when two photons interfere destructively at a point on a screen in Young's double slit experiment ?
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33 views
Physical significance of effective wave function
In Yanhua Shih's book on quantum optics, the coherence functions are expressed in terms of effective wave function. Here are the expressions for single photon wave packets.
To derive the coherence ...
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1answer
507 views
Neutrinos vs. Photons: Who wins the race across the galaxy?
Inspired by the wording of this answer, a thought occurred to me. If a photon and a neutrino were to race along a significant stretch of our actual galaxy, which would win the race?
Now, neutrinos ...
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3answers
37 views
Interaction photons-matter and dimensional analysis
I know that when photons pass through matter, the law that describes the intensity in function of the thickness is:
$$I(x)=I_0 e^{-\mu x}$$
where $\mu = \rho \frac{N_a}{A} \sigma$ and ...
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2answers
89 views
Do photons have mass? [duplicate]
As a student in a highschool physics class, my teacher has repeatedly told me that photons are massless. Yet, I have also heard from other sources that photons have momentum. If photons were to have ...
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0answers
49 views
How does QED deal with wavelength of quanta [duplicate]
Since QED treats photons as individual units (quanta) how does it treat the concept of the "wavelength" associated with the photon?
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1answer
58 views
Finding the maximum kinetic energy of any photoelectrons?
An incident photon, $f=5.5\times 10^{14}\ Hz$, hits a metal with a work function of $2.8\ eV$.
Find the maximum kinetic energy of any photo-electrons (in Joules).
I'm confused exactly how to do ...
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1answer
35 views
Color of a Metal's Threshold Wavelength?
How do I find the color of the threshold wavelength if the metal has a threshold wavelength of $\mathrm{6.5\times 10^{-7}m}$? I know that converts down to $\mathrm{650\ nm}$, but can I still use the ...
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1answer
27 views
Color of an incident photon?
If the incident light at 360nm causes photoemission of electrons, wouldn't the color be ultraviolet? I know that really isn't a color, but that's what my chart of the light spectrum says.
Unless I ...
8
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1answer
155 views
How the inverse square law in electrodynamics is related to photon mass?
I have read somewhere that one of the tests of the inverse square law is to assume nonzero mass for photon and then, by finding a maximum limit for it , determine a maximum possible error in ...
2
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3answers
72 views
What is the cause the light is affected by gravity? [duplicate]
I know that photons have no mass and that a photons exist only moving at the speed of light. So what is the cause that a massive astronomical object can bend a ray of light?
I have two thoughts, but I ...
3
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2answers
74 views
Transfer of electron energy to atoms (heating up of matter by absorption of photons)
If an electron absorbs a photon to get exited to a higher energy level, it should either come back to same state or any other lower state by emitting the required photon. How then can there be a net ...
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2answers
98 views
What is the mass of a photon moving at the speed of light? [duplicate]
What is the mass of a photon moving at the speed of light?
And if it does not have mass, how is it affected by gravity?
Also why does Einstein's general relativity support that a gravitational wave ...
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0answers
62 views
Conservation of Angular Momentum: atomic transitions vs exciton decay
I have a question about the role of photon angular momentum in two different sets of selection rules:
In atomic transitions within the dipole approximation, I've seen the selection rule as:
$\Delta ...
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2answers
103 views
Seeing colors: photons vs waves
As an atmospheric physics major I am familiar with electromagnetic radiation in the atmosphere and what dictates what wavelength objects will emit at. When observing radiation in the atmosphere it is ...
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3answers
218 views
Does a photon have mass? [duplicate]
I have seen questions assume photons have no mass. But I have not seen any questions that directly ask whether or not photons have mass.
If photons have no mass, then how do they occupy space? How ...
3
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0answers
100 views
Quantum Electrodynamics
I was wondering if anyone could give a simple explanation of how light interacts with matter. From what I have read in QED, electrons will repel each other because of their ability to emit and ...
4
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2answers
177 views
Are there “gaps” in light, or will it hit everywhere?
Not sure how to word my question.
Picture a light source in vacuum, so nothing disturbs the light (or similar conditions), 2d.
If I move very, very far away, will it happen that some of the light ...
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1answer
39 views
hurdles in creating (close to) infinite images
Let's put an object(hypothetical superman) inside a "well sealed" box containing only mirrors. Is it possible to create number of images that will be close to infinity, assuming that resolution of our ...
4
votes
1answer
119 views
Are there 2 kinds of photons, one that mediate the electromagnetic interaction and the other the quanta of light?
It is usually said that photons are the force carriers or the mediators of the electromagnetic forces between electric charges. At the same time we know also that electromagnetic waves on the quantum ...
4
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2answers
183 views
How photons represent colors that you see?
Right now, my understanding is that, a mixture of photons of many different frequencies is perceived as white by your eye. While no photons at all, is perceived as black. And photons with the blue ...
4
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2answers
167 views
Do protons exchange photons with electrons?
I'm sorry for this question but, I just don't get it. According to the electromagnetic field theory, electrons repel each other by exchanging photons. How do protons attract electrons, by photon ...
9
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1answer
101 views
If light is linearly polarized, does it have some spatial extent?
If light (a photon) is linearly polarized, say vertically, does it have some vertical spatial extent (perhaps in amplitude)?
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3answers
114 views
Couldn't we measure electrons with good enough technology? [duplicate]
I am a bit confused about the Heisenberg's Uncertainty Principle - just read about it in How to Teach Physics to Your Dog, by Chad Orzel. He states that the reason electrons can't be measured is ...
3
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1answer
86 views
How can photons exert gravity if they are wave-like?
As a reference, see this question: Does a photon exert a gravitational pull?
It turns out the answer is "Yes" -- but this does not seem consistent with light being wave-like.
I am imagining a ...
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1answer
76 views
Is this mental picture of photon correct?
What is exactly meant by a statement like "there are about 400 photons per cubic cm in certain region"? Should I mentally picture this as 400 discrete photons enclosed in that volume, each moving at ...
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0answers
24 views
Why photons can't escape black hole? [duplicate]
Photons do not have (rest) mass. Then why are they attracted by the black hole? And is it possible that a photon crossing a black hole from a little distance could get accelerated due to the force?
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0answers
39 views
Photon detection rate for pure / mixed states coming from single mode point source
Let the pure states be in superposition of horizontal and vertically polarized basis states. They are arriving at the point detector one at a time. So, a pure state is $|\Psi\rangle = \alpha|V\rangle ...
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2answers
155 views
Why does Quantum Electrodynamics Allow a Photon to Exist Temporarily as a Positron and an Electron?
In this question...
Why does a photon colliding with an atomic nucleus cause pair production?
...I asked why a photon colliding with a atomic nucleus can become an electron and a positron. The ...
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1answer
62 views
Absorption cross section for direct dissociation and predissociation - Photoelectric absorption
Why the absorption cross section in direct dissociation process is wide and structureless while the absorption cross section in the predissociation process is structured and containing lines which are ...
