17
votes
Accepted
Failure of Newton's corpuscular theory and success of photon theory of light
The corpuscular theory was opposed to the wave theory, and was rejected when diffraction experiments confirmed the wave theory. The blackbody spectrum also confirmed the wave theory at low frequencies,...
- 3,239
12
votes
Why is Equation of State of Photon gas different from the Equation of State of Boson gas?
The equation $p = 2u/3$, where $u$ is kinetic energy density, is true for any non-relativistic, non-interacting, point-like particles, whether they be spin 1 bosons or spin 1/2 fermions. Your first ...
- 110k
10
votes
Failure of Newton's corpuscular theory and success of photon theory of light
As an example, when using the corpuscular theory refraction of light and Snell’s Law is predicted using Newtonian Mechanics but a requirement of the theory is that the speed of light in glass is ...
- 77k
9
votes
Accepted
Why is Equation of State of Photon gas different from the Equation of State of Boson gas?
Photons are indeed bosons (spin 1), and from what I can see in the book all the formulas are written for a classical system of bosons. Photons are massless relativistic particles,so when you try to ...
- 118
7
votes
Doubt on photoelectric effect
You are confusing the energy of a single photon with the energy of the light beam.
Increasing the intensity of light (while keeping the frequency $f$ constant) does not increase the energy per photon, ...
- 25.7k
7
votes
What gives particles mass? Also why are particles like photons considered massless when they have energy and momentum?
The idea that a photon is massless is a pedagogic convention, that has not always held sway. When I was taught special relativity in the '70s, there were two kinds of mass that were distinguished. ...
- 2,696
5
votes
Does a photon have a minimum energy level, below which it disappears?
Lorentz invariance implies that a photon can have any amount of energy.
In particular, if a photon has the four-momentum $(E, E, 0, 0)$ (that is, it travels in the direction of the positive x-axis) ...
- 4,595
3
votes
What gives particles mass? Also why are particles like photons considered massless when they have energy and momentum?
Mass is energy that a particle has when it is at rest. Photons are never at rest, and so don't have mass. A related fact is that in the limit that the photon's momentum goes to zero, its energy also ...
- 33.3k
3
votes
Will 'free' photons exert gravitational force
Do photons have gravity according to GR?
A (classical) electromagnetic field has an associated stress-energy tensor all by itself. See wikipedia. The question of whether and how individual photons ...
- 8,398
3
votes
Are gamma rays the limit of the frequency photons can attain, and if yes, why?
Which Universal factor imposes this limit of electromagnetic radiation, and what is it called?
In the table here for the electromagnetic spectrum the energy of a gamma rays is given in megahertz ...
- 221k
2
votes
Accepted
Are gamma rays the limit of the frequency photons can attain, and if yes, why?
Gamma rays doesn't impose any frequency limit as per definition, because gamma rays just means electromagnetic waves which have frequency $\gt 10^{18}~\text{Hz}$. Upper frequency limit is imposed by ...
- 7,202
2
votes
Phonon, photon have chemical potential equal to zero
The number of modes of the phonons is $3N$. However, for each mode, the number of phonons is not conserved.
An analog is that we have $3N$ different harmonic oscillators, and each of them can be in a ...
- 1,446
2
votes
Accepted
How Chadwick concluded that the particles are neutrons but not photons?
The WP article I linked summarizes that
In 1931, Walther Bothe and Herbert Becker found that if alpha particle radiation from polonium fell on beryllium, boron, or lithium, an unusually penetrating ...
- 47.2k
2
votes
Accepted
How do retinal cones see color when the cones pickup photons and not waves?
The interaction between photons and chemistry, eg, via atomic orbitals of single atoms, is a classic tool for understanding quantum mechanics, so there shouldn't be any surprises that the absorbing ...
- 2,735
1
vote
Are photons with different frequency distinguishable?
Let's consider photons in a cubical box (a cavity) with side length $L$. The modes of the electromagnetic field are labeled by:
The integers $\{n_x, n_y, n_z\}$, which are related to the wavenumbers $...
- 33.3k
1
vote
What does it exactly mean when we say that a photon or light is "frozen" at the event horizon?
It doesn't mean a lot.
Event horizons are outward-moving lightlike surfaces, but the curvature is such that usually their overall size doesn't increase (except during black hole formation, accretion ...
- 17.3k
1
vote
Is light's momentum $0$?
If you start with the energy momentum relation
$$
E^2 = \left(m_{0} c^2\right)^2 + \left(pc\right)^2
$$
where $m_{0}$ is the rest/invariant mass, and apply it in the rest frame (where $p = 0$), you ...
- 2,718
1
vote
Reducing the filament voltage has no effect on the maximum photon energy produced by characteristic or Bremsstrahlung radiation. TRUE - why?
The filament voltage controls the filament temperature, which controls the electron current, but not the electron energy. Thus, increasing the filament voltage increases the flux of x-ray photons, but ...
- 3,239
1
vote
Phonon, photon have chemical potential equal to zero
$3N$ is the number of available vibrational modes, where $N$ is the number of atoms in the solid. Each mode can have a non-negative number of phonons, so the total number of phonons is not $3N$. In ...
- 7,257
1
vote
Accepted
How does a single slit produce coherent light?
TL;DR: temporal vs. spatial coherence.
To add to other answers: there exist time coherence (or temporal coherence) and spatial coherence. While the former results from the presence/lack of correlation ...
- 37.2k
1
vote
How does a single slit produce coherent light?
Single slit can have two effects:
It effectively decreases the angular size of the source. Smaller source size results in better time coherence, because there is smaller spread in distances that ...
1
vote
Why Photon gas's Equation of State Diverges?
I couldn't quite follow your calculations for $U$, especially when the bracket appears line $3$. Normally you do a simple integration by parts to get the state equation. You have for non-interacting ...
- 1,145
1
vote
Accepted
Ensemble associated with a system of Photons
The formula looks like a formula in the Canonical Ensemble but is the genuine result of a Grand Canonical Ensemble calculation at the $\mu=0$ condition.
The way to see it is as follows.
The grand ...
- 23.3k
1
vote
Ensemble associated with a system of Photons
There are two perspectives, the first one is to consider this as an effective application of the Grand Canonical Ensemble, with chemical potential $\mu=0$. However, the specific choice the chemical ...
- 1,145
1
vote
Accepted
Is photon drive reaction less propulsion?
It will not violate Newton's third law, since although photons have no mass, they still have momentum given by $$p=\frac Ec$$ where $E$ is energy and $c$ the speed of light.
- 24.8k
1
vote
Why the emitted photon has exactly the same energy,phase and direction as the incident photon in stimulated emission?
the emission is triggered by an incident photon. assumes emission photon has equal energy. Now when electrons fall back to low energy EM wave emitted if we relate this emission due to electron ...
1
vote
How does stimulated emission work, exactly?
I just don't understand one thing, if photons carry energy, shouldn't
the electron be forced to higher excited states?
This typically does not happen because the photon usually considered when ...
- 1,600
1
vote
What are electromagnetic fields made of?
The most fundamental thing in physics, is the way that we conduct phyiscs. And physics will be as good as we are conducting it.
We conduct physics by using 1) logic and 2) the scientific method.
In ...
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Only top scored, non community-wiki answers of a minimum length are eligible