# Tagged Questions

Photons are electromagnetic waves. They exhibit particle-like qualities in many situations and have zero rest mass.

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### Speed of Light in a Medium [duplicate]

For light travelling in a medium with refractive index greater than one: The "average" speed of light is slower than the speed of light in a vacuum. As far as I know, the instantaneous speed of light ...
1answer
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### Life of a photon [duplicate]

I am a student of class 12th and as far as i know when anything reaches about 99.99% of the speed of light it starts traveling in time or time for it slows down so that it don't breaks the speed ...
1answer
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### Two-photon scattering: colours

Is there a particular conservation principle that necessitates that the outcoming photon pair has the same frequencies as the incoming photon pair? I'm thinking in particular of these Feynman-like ...
1answer
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### Quantum Mechanics proved incorrect. Bohr - Einstein debates concluded?

"Photons act like they go through two paths, even when we know which they took". Please refer the above link and its conclusion. I am an Engineer. What I infer from this is :- This proves ERP. ...
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### Photons interact with themselves

We know that photons are the antiparticles of themselves and if they interact with each other through higher order process do they annihilate and again produce photons? Here is the Phys.SE question ...
4answers
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### Collision of two photons

Could someone explain me how will be look like collision of two photons? Will they behave like: Electromagnetic waves, they will interpher with each other and keep they wave nature Particles and ...
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### How to make DIY flight detector for double slit experiment?

I want to reproduce double slit experiment. So, is it possible to build flight detector (situated near one slit) at home? Is it possible to buy it somewhere?
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### Thermionic emission and delayed emission

I want to understand the concepts behind the thermionic emission. In thermionic emission, the energy randomization occurs and the energy may be split to electronic or roto-vibrational states. If this ...
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### How does a photon experience space and time?

To an an external observer it appears that time has stopped for photon. But this relation is reflexive, so for an observer travelling with the photon it appears the universe has stopped everywhere. ...
1answer
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### Frequency Of Light

I am confused on few topics... What is meant by "Frequency of Light"? Does the Photon(s) vibrate, that is known as its frequency? If the Photons vibrate, then they have a specific frequency, then ...
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### What is a photon's speed inside a dieletric?

We know that EM waves are slowed down in a dielectric. But at what speed does the photons that make up the wave travel? Do they always travel at the speed $c$, but colliding/being absorbed and ...
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### How fat is Feynman’s photon?

According to my calculations, it is a lot skinnier than Airy’s photon, but still a whole lot fatter than a straight line. So, how does a photon get from point A to Point B? The ray optics ...
5answers
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### Confusion regarding photons?

I'm still in high school, and while I can't complain about the quality of my teachers (all of them have done at least a bachelor, some a masters) I usually am cautious to believe what they say ...
3answers
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### Redshifted photons

When a photon is emitted from a far away source and then measured by an observer, there is a loss of energy or redshift which takes place. Why does this happen? I have read this similar post, however ...
1answer
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### Does photon have size measurement because of its particle nature

Does photon have size measurement because of its particle nature like electron's 3.86*10^-13m etc..
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### Is there a maximum amount of photons that can exist in a certain amount of space?

If you have a set amount of space, lets say 10 cubic centimeters, and you would be able to trap photons in there. If you would then add more and more photons to that space, could you then go on ...
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### How photons move along with EM wave?

So the wave moves like. a wave, it moves up and down, up and down. But how do photons move? Do they follow the same path or do they just go straight forward without oscillating?
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### Does the electromagnetic field “spin”?

Due to electron "spin", a small magnetic field is produced. Maxwell's equations imply that magnetic fields are due to changes in electric fields. Is the magnetic field produced then because the ...
1answer
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### Any suggestions for units conversion? [duplicate]

Possible Duplicate: Photometer: measured Irradiance L converted to photon rate I am conducting a experiment where stimulus output of $470\ nm$ is measured by a radiometer at \$30\ \mu W\ ...
3answers
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### Compton Scattering

Compton Scattering essentially states that when a photon of a given wavelength hits an electron the energy level of the electron changes and the photon has its wavelength changed. This seems to be ...
1answer
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### Graviton and photons interaction

If one believes in the theory of gravitons then by viewing a black hole you see gravitons affect photons. This in turn leads to the conclusion that force carrier's mass equivalences allow them to be ...
1answer
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### Specific electron energy gap values $E_{i+1}-E_i$ vs. photons with arbitrary energy $\hbar \omega$

The energy levels of electrons in an atom are quantized $E_i$. A photon of a specific momentum $\vec p$ and energy $$\omega=(E_{i+1}-E_i)/\hbar$$ hits an atom and gets absorbed. Okay now say the ...
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### Photons emitted by radioactive source

Can we calculate the number of photons emitted per second by a radioactive source (gamma) ? we can take 100g of barium-133 as an example
1answer
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### Speed of light and lorentzian factors [duplicate]

Possible Duplicate: How can a photon have no mass and still travel at the speed of light? If light travels at the speed of light, and anything with rest mass will experience relativistic ...
2answers
157 views

### statistics for photon counts in photomultiplier

It seems that a common statistical model for the count numbers of a photomultiplier is a Poisson distribution whose parameter $\lambda$ equals to the square-root of the number of counts.(e.g. ...
1answer
125 views

### Confused about fire?

Im confused about fire. The way I see it : Heat creates (kinetic) energy in mass and this creates stronger vibrations of atoms. When those vibrations are strong enough the electrons interact ...
1answer
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### Gravitational redshift derivation

When we derive gravitational potential it is dependant only on (rest) mass $m$, but i have seen a derivation of gravitational redshift equation placing relativistic mass $\widetilde{m}$ instead of ...
2answers
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### 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 ...
2answers
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### Photons in a gravitational field

I have been really staring for a while in a MP-Beiser book and I totally disagree with a statement he does there. On a page 85 he states that photons act as they have a mass $m$. He derives this by ...
1answer
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### How can the 5-photon absorption coefficient be estimated?

Imagine a large bandgap material which is irradiated by an intense laser beam. If the photon energy is only high enough for 1/5 of the bandgap, is there a way to approximate the absorption by 5-photon ...
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### Photoionization equation

I really need help understanding this equation ,i am new to quantum mechanics and i cant understand the math, so i need every single symbol to be explained or given a value if it is a constant , ( ...
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### Why do Photons want to be together?

So I've heard that when a photon flies by a atom excited enough to release a photon there's a good chance it will. Because Photons want to be together and have the same direction etc? Is this true? ...
1answer
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### Does photon possesses no time to cover any arbitrary distance?

Photon travel 8 minutes (with speed $c$) from the sun to reach the earth. Any particle (or space-ship) with velocity $0.99 c$ covers the same distance (93 millions km) within less than 2 minutes ...
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### Why does $\mathcal L = -\frac14 F^{\mu\nu} F_{\mu\nu}$ imply Photons are massless?

The Lagrangian $\mathcal L = -\frac14 F^{\mu\nu} F_{\mu\nu}$ with $F_{\mu\nu} = \partial_\mu A_\nu - \partial_\nu A_\mu$ results in the four-potential's equation of motion  \underbrace{\partial^\mu ...
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### Polarization photon and Stokes parameters

I have the following situation: About the polarization of the photon, I introduce the basis: Horizontal polarization $|\leftrightarrow>=\binom{1}{0}$ Vertical polarization ...
2answers
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### Do photons lose energy while travelling through space? Or why are planets closer to the sun warmer?

My train of thought was the following: The Earth orbiting the Sun is at times 5 million kilometers closer to it than others, but this is almost irrelevant to the seasons. Instead, the temperature ...
2answers
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### How does scattering work?

Why is the sky blue? I was always taught in high school that light with wavelength $\lambda$ acts like a little particle that wiggles up and down through space (in proportion to its magnitude). I was ...
1answer
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### Photons and Relativity

Consider a Photon from Sun and travels with a velocity $c$. Now think we are that photon. For us, it looks like Sun is moving away from us with a velocity $c$. So, why don't we get attracted back ...
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196 views

### What do massive photons have to do with superconductivity?

I keep reading that the idea of massive photons leads to an explanation of the Meissner effect but I fail to see how photons are involved with the repulsion of fields inside a superconductor. How ...
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### Photon pumping in Laser

Let's consider a ring laser where the laser must pass through the gain material before it is sent toward a partially reflective surface $\ R=1-T$. The other mirrors are perfect reflectors with \$\ ...
3answers
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### How many percent of the visible light reaching the Earth are from other stars than the Sun?

How many percent of the whole visible light reaching the Earth are from other stars than the Sun? Is it maybe 0,5 - 1% or is my guess already too much? I am interested mainly in visible light, but ...
4answers
400 views

### Why is the $S_{z} =0$ state forbidden for photons?

If photons are spin-1 bosons, then doesn't quantum mechanics imply that the allowed values for the z-component of spin (in units of $\hbar$) are -1, 0, and 1? Why then in practice do we only use the ...
1answer
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### Photons arriving from the Sun

Given that the Sun is a bit less than 10 light minutes away from Earth, is it correct to assume in principle (I understand actual processes in the core of the Sun make the situation at a photon's ...
2answers
159 views

### What happens to the wavelength/frequency of a photon as it passes through an event horizon?

I've asked a similar question about photons and black holes but wanted to rephrase it more specifically, so here goes... Ever since I learned how a photon's wavelength and frequency are indivisibly ...
1answer
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### Where can you get a photon detector?

Say I'm doing the double-slit experiment with photons as the particle and want to add a detector just behind each slit to eliminate the interference pattern. Where would I get a detector like that?
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### Ejected Electrons with 0 KE?

So I was taught that: Kinetic Energy (of electron) = Energy (of photon) - Ionization Energy If E(photon) = IE, then KE=0 of the electron. What does this physically/theoretically mean? My current ...
3answers
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### Mechanism for the gravitational field generated by photons

This question follows from a schooling I received in this thread. I figured that photons do not interact with gravity, except when they've spontaneously converted into a particle-antiparticle pair. ...
1answer
211 views

### What really is Planck's constant and what are its origins?

In the physics texts I have read and other info online, they says Planck's constant is the quantum of action or that it is a constant of the ratio of the energy of a particle to its frequency. Im ...
1answer
107 views

### How to relate photon's higher frequency to time dilation?

The usual explanation for photon's higher frequency in lower altitudes (higher gravity), when the photon is going downward towards a massive body, is that gravitational potential energy is converted ...
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### Modeling the probability of a photodiode measuring photons targets at a neighbor

In current digital cameras, sensors are arrays of photodiodes which "transform" photons energy to electrons. I am aware that the probability of a photon to generate an electron is modeled by a Poisson ...
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