All Questions
Tagged with classical-mechanics optics
37
questions
18
votes
7
answers
2k
views
When/why does the principle of least action plus boundary conditions not uniquely specify a path?
A few months ago I was telling high school students about Fermat's principle.
You can use it to show that light reflects off a surface at equal angles. To set it up, you put in boundary conditions, ...
- 103k
14
votes
3
answers
2k
views
Is it possible to apply a torque without a moment arm?
In some statics problems, the question may say something like "a torque is applied about Point B". I've always assumed this was a simplification and the torque was created using a force and a moment ...
- 421
12
votes
6
answers
8k
views
Light's inverse square law: Does it require a minimum distance from the source?
Does the inverse square law begin to take effect the moment light leaves its source? For example, does light's intensity decrease, i.e. does the area in which the photons might land increase, at a few ...
- 539
11
votes
3
answers
2k
views
Liouville's theorem and gravitationally deflected lightpaths
It is customary in gravitational lensing problems, to project both the background source and the deflecting mass (e.g. a background quasar, and a foreground galaxy acting as a lens) in a plane.
Then, ...
- 3,755
6
votes
2
answers
1k
views
In geometric optics we treat light as a collection of particles?
I've been reading the book "Geometric Mechancis" by Darryl Holm and the in the first chapter he treats geometric optics. There the author talks about light rays and those light rays looks like ...
- 36.4k
5
votes
3
answers
630
views
Is Principle of Least Action a first principle? [closed]
It is on the basis of Principle of Least Action, that Lagrangian mechanics is built upon, and is responsible for light travelling in a straight line.
Is its the classical equivalent of Schrodinger's ...
4
votes
3
answers
292
views
Lossless beam splitter relations
Wikipedia says that for a beam splitter $$\begin{bmatrix}E_{c}\\
E_{d}
\end{bmatrix}=\begin{bmatrix}r_{ac} & t_{bc}\\
t_{ad} & r_{bd}
\end{bmatrix}\begin{bmatrix}E_{a}\\
E_{b}
\end{bmatrix}$$ ...
- 1,038
3
votes
2
answers
255
views
How is mass defined by special relativity?
I am eagerly interested in all kinds of areas of physics. As the question of mass has been around for a pretty long time, I am interested about what modern physics namely special relativity says about ...
3
votes
1
answer
924
views
Origins of the principle of least time in classical mechanics
Is it possible to derive the principle of least time from the principle of least action in lagrangian or hamiltonian mechanics? Or is Fermat's principle more fundamental than the principle of least ...
- 1,352
3
votes
1
answer
90
views
Reflection coefficient: Acoustics vs Mechanics
I recently tried to derive the reflection coefficient $R$. This is not a complicated task, however after making some literature research I found two derivations which arrive at seemingly different ...
- 469
3
votes
1
answer
238
views
Explaining why rubbing two surfaces together by hand create convex and concave shapes?
From this video (relevant timestamp included in URL):
https://www.youtube.com/watch?time_continue=768&v=ABRysNzcdvw&feature=emb_title
It shows how rubbing two surfaces together by hand with ...
- 799
3
votes
0
answers
46
views
Relating Brachistochrone problem to Fermat's principle of least time [closed]
When I came across the Brachistochrone problem, my teacher said we could relate it to Fermat's principle of least time.
So, we could make many glass slabs of high $\mathrm dx$, and every slab has a ...
- 31
2
votes
1
answer
1k
views
relation between Schrodinger equation and wave equation [duplicate]
I have always been confused by the relationship between the Schrödinger equation and the wave equation.
$$ i\hbar \frac{\partial \psi}{\partial t} = - \frac{\hbar^2}{2m} \nabla^2+ U \psi \hspace{0....
- 778
2
votes
2
answers
39
views
Is this interference or superimposed image?
When you overlay two identical screens a new patterns forms as they offset. See image:
The two screens are not touching or interacting with each other.
Are the different patterns we see as the two ...
- 4,083
1
vote
2
answers
1k
views
$\omega(k)$ and $k(\omega)$ about waves
Wave propagation is characterized by the wavenumber $k$ and the angular frequency $\omega$. Sometimes (like in this answer) the relation $\omega (k)$ is preferred; sometimes instead $k ( \omega)$ is ...
- 767