# Tagged Questions

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1answer
62 views

### Infinite reflection of light and the conservation of energy / momentum

First off, I confess I'm no physicist, but I have been asking people with a more extensive knowledge this one question, without a definitive answer so far. Basically, I'm playing around with the idea ...
1answer
58 views

### Single photon's effect on conservation of momentum?

When your looking at basic Compton theory you find that if you shoot a stream of photons at a particle (usually atoms or electrons), then you have the basic laws of conservation of momentum. The ...
3answers
122 views

### If photons can be absorbed by electrons, wouldn't that mean light has a charge? [duplicate]

I am a biochemistry and molecular biology major. If photons can be absorbed by electrons, wouldn't that mean light has a charge? Electrons only attract positive charges. Isn't it?
2answers
85 views

### Does performing a measurement on a system change its internal energy?

I'm studying Quantum Mechanics in my spare time from a general point of view (no technical details) so some fundamental question came into my mind: How is it possible to detect a single photon ...
0answers
31 views

### How does a photon leave trace of its polarization state in a photon detector but not trace of which direction it came in?

Some quantum erasure experiments involve polarization of photons. In one such experiment with a double slit, a horizontal polarizer is used in front of one slit, and a vertical polarizer is used for ...
4answers
107 views

### the temperature of photon and its energy

Do photons have temperature? If not, does it mean that photon lose energy while travelling through space? As the planets farther away from the sun are comparatively cooler than the one that are ...
1answer
152 views

### Single photon interference experiment

In short: the question is, does the length of the path affect the outcome of detecting a photon? Consider the single photon beam splitter experiment. Does the probability of detecting the photon ...
3answers
150 views

### Does light really “travel”?

From what I've so far understood about light, a photon is emitted somewhere and after some time it's absorbed somewhere else. Have we had experiments that confirm the path taken or something akin to ...
4answers
271 views

### Why does a photon colliding with an atomic nucleus cause pair production?

I understand that the photon needs to have enough energy to produce a lepton and it's antimatter partner, and that all of the properties are conserved, but why does the photon do this in the first ...
0answers
42 views

### If photons don't have mass then why do we calculate their momenum? [duplicate]

As much I know photon do not have any mass. But while studying my course book saw a topic which included calculation of momentum of photons. I was wondering why was that. Please clear my confusion?
0answers
54 views

### How many orders of magnitude in energy spans the domain of validity of the Standard Model?

I am wondering if it makes sense to state that the upper limit is roughly 1012 eV (up to know the physics probed by the LHC seems to be pretty consistent with the SM) and the lower one is ... the ...
1answer
99 views

### Photons, no energy? [duplicate]

I am only 14, so I don't know much about physics, and I would appreciate help on this topic. A photon, is said to have 0 mass. However, they carry energy, as electromagnetic radiation. Albert ...
2answers
196 views

### Kinetic energy of a photon and Schwarzschild radius

I have read here, that $\frac{1}{2}mv^2$ must not be applied on a photon ever. If i want to calculate escape velocity $v_e$ i need to use $\frac{1}{2}mv^2$ because we say that kinetic energy ...
3answers
711 views

### Amplitude of an electromagnetic wave containing a single photon

Given a light pulse in vacuum containing a single photon with an energy $E=h\nu$, what is the peak value of the electric / magnetic field?
2answers
228 views

### Photon energy - momentum in matter

$E = h\nu$ and $P = h\nu/c$ in vacuum. If a photon enters water, it's frequency $\nu$ doesn't change. What are its energy and momentum : $h\nu$ ? and $h\nu/c$ ? Since part of it's energy and momentum ...
0answers
34 views

### Why, in EXAFS spectrum, does the absorption coefficient monotonically decrease with increasing photon energy?

It is common knowledge that following the absorption edge, where the photon energy equals the binding energy of a core electron, a monotonic decrease in the absorption coefficient with increasing ...
1answer
159 views

### Does the Photino have mass or is it mass-less like the photon

Does the photino in super-symmetry have a mass, Or is this different in different super symmetric models?
0answers
100 views

### Why angular momentum applies to emitted photons, and how it affects the emitting atom's quantized system

From what I've read, photons have spin of 1 (I guess possible by their relativistic mass), and when a photon is emitted from an atom, the production of this spin affects the balance of the atom's ...
1answer
145 views

### Why photons are emitted because of changes to electron behavior

Explanations I have read of why photons are emitted from atoms mention electrons being 'excited' to another energy level, and then returning to their base level, releasing a photon. I have also seen ...
3answers
260 views

### What is the massless limit of massive electromagnetism?

Consider electromagnetism, an abelian gauge theory, with a massive photon. Is the massless limit equal to electromagnetism? What does it happen at the quantum level with the extra degree of freedom? ...
2answers
598 views

### How many photons can an electron absorb and why?

How many photons can an electron absorb and why? Can all fundamental particles that can absorb photons absorb the same amount of photons and why? If we increase the velocity of a fundamental ...
0answers
76 views

### Is there any optical experiment that can not be explained by photon model defined in QED?

Some author(in the paper of Evolution of the modern photon) mentioned that photon cannot account for the zero intensity through two crossed polarizators by 90 degree. Why so?
0answers
65 views

### What about the photons that make you see ? [duplicate]

Possible Duplicate: What determines color — wavelength or frequency? Explanation about black color, and hence color I understand that what we see are the reflected light from other ...
1answer
197 views

### What is the difference between infrared heat and “regular” heat?

In Feynman's terms temperature is the speed at which atoms are 'jiggling'. Now, let's suppose I've just eaten a sizable dinner, and my body temperature just got a tad up. Am I emitting more photons in ...
3answers
272 views

### Why do photons travel?

Photons travel at the speed of light. Is there a known explanation of this phenomenon, and if yes, what is it? Edit: To be clearer, my question is why do photons travel at all. Why do they have a ...
1answer
162 views

### Expression for the (relativistic) mass of the photon [closed]

I started learning a bit ahead from an old physics book, and they were discussing the photoelectric effect and after that Planck's hypotheses and energy quantas. The book said that the mass of a ...
3answers
274 views

### If electromagnetic fields give charge to particles, do photons carry charge?

As I understand these two statements: An electromagnetic field gives particles charge A photon is a quantum of electromagnetic field It must mean that a photon carries charge. But I guess it isn't ...
0answers
64 views

### polarization - quantum point of view

polarization could be easily imagined in classical model: direction of E vector. is there any simple image for polarization of single photon?
0answers
97 views

### Does this photon emission problem even make sense?

I came across this question in an introductory physics course awhile back and I never got over it: "A hydrogen atom has an electron in the n=5 orbit, what is the maximum number of photons that might ...
4answers
346 views

### Does $p=mc$ hold for photons?

Known that $E=hf$, $p=hf/c=h/\lambda$, then if $p=mc$, where $m$ is the (relativistic) mass, then $E=mc^2$ follows directly as an algebraic fact. Is this the case?
0answers
68 views

### Trajectory of a photon due to a constant/uniform gravitational force [closed]

I have a small problem of physics linked to a basic ray tracing algorithm. My problem is the following : At $t = 0$, a photon at the position $(x_0 = x_\text{min},y_0 = y_\text{min})$ with the ...
1answer
66 views

### Computing gravitational deflection of light knowing $\phi$ and $-\nabla \phi$?

I have a 3D cartesian grid an in each grid I know the gravitational potential $\phi$ and the 3D gravitational field $-\nabla \phi$ (with a Newtonian approach). How to compute the path of a photon in ...
1answer
94 views

### Exist some relationship between irradiance units and wavelenght of the incident sunlight?

Exist some relationship between irradiance units and wavelength of the incident sunlight? What about irradiance? I want to establish a relationship between wavelength and irradiance, because I would ...
1answer
161 views

### Will photon's energy be exactly same after million years?

If photon will travel for million years without collisions, what subtle effects can be accumulated ? Gravity fields affect trajectory, but is energy completely intact after fly by ? Photon has its ...
2answers
97 views

### Massless particle as a result of annihilation of “heavy” particles

How can a massless particle such a photon be the result of electron-positron annihilation? What about the law of conservation of energy? Is a valid explanation that the pair's energy transforms itself ...
0answers
86 views

### Does the passage of time effect a photons entanglement with another?

I recently read an article about "Delayed-choice entanglement swapping". Here is an excerpt from the article: Delayed-choice entanglement swapping consists of the following steps. (I use the ...
2answers
585 views

### Does a photon exert a gravitational pull?

I know a photon has zero rest mass, but it does have plenty of energy. Since energy and mass are equivalent does this mean that a photon (or more practically, a light beam) exerts a gravitational pull ...
2answers
188 views

### Wavelength of photon changes as it rises from a planet's surface(acc. to this equation)?

The setup assumes a large mass(Earth?) an a photon launched from its surface initially. The wavelength of the photon on launch is known. Then the new energy of the photon is compared with energy it ...
1answer
132 views

### True or false? Particle physics [closed]

It is not possible to prove the point of origin of a photon It is not possible to prove the point of origin of a free electron It is not possible to prove that protons or neutrons exist inside a ...
3answers
475 views

### Can a photon be emitted with a wavelength > 299,792,458 meters, and would this violate c?

Just curious if the possibility exists (not necessarily spontaneously) for a photon with a wavelength greater than the distance component of c to be emitted, and would this inherently violate the ...
1answer
380 views

### Photon spin projection to arbitrary axis

For photons (and any massless particle) we consider only a spin projection into the direction of motion (helicity). Why it's meaningless to talk about projection of photon's spin into some arbitrary ...
1answer
205 views

### What is the mass of a photon in non-empty spaces?

It is a well known result of the special theory of relativity that the photon has no rest mass, because for a particle to attain the speed of light, it must have zero rest-mass. I will not dig into ...
3answers
769 views

### Conservation of energy and Doppler effect?

From what I understand, the frequency of light coming from the source moving towards an observer increases. From $E=hv$ , this implies increase in energy of photon. What really is confusing, is ...
2answers
779 views

### Wave / particle duality question for sound and light

Sound is usually referred to as just "sound waves" - we do not talk about a "sound particle" and only as a wave or "matter wave." Could something similar apply to light i.e. that there really is no ...
3answers
1k views

### Scattering of light by light: experimental status

Scattering of light by light does not occur in the solutions of Maxwell's equations (since they are linear and EM waves obey superposition), but it is a prediction of QED (the most significant Feynman ...
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