0
votes
0answers
28 views

Poisson equation solver with specific boundary condition

I want to solve 2d Poisson equation with this Boundary conditions below $$u(-5,y) = 0 , \\ \frac{\partial u(x,y)}{ \partial x} = 0 \,\,{\rm at}\,\, x = -5\\ u(x,-5) = u(x,5)$$ Now my question is ...
0
votes
0answers
19 views

What could be the use cases of optics in a computer algebra system? [on hold]

I am working on optics module in sympy. As of now I've only implemented Transverse wave, Medium and some functions for ...
1
vote
0answers
39 views

Laplacian in tensor [on hold]

Find $\vec \nabla^2\phi $ when $$ds^{2}=-dt^{2}+a^{2}(t)[dx^{2}+dy^{2}+dz^{2}] $$ or $$g_{ij}=\begin{bmatrix} -1 & 0 &0 &0 \\ 0 &a^{2}(t) &0 &0 \\ 0&0 ...
15
votes
3answers
4k views

How would an X-ray scanner identify a mirror?

A mirror is normally used to reflect Electromagnetic radiation also known as photons (light) and in airport security or medical facilities, they use X-rays to detect anomalies inside objects or bodies ...
2
votes
1answer
22 views

Does Light (EM Signal) undergo accelration during reflection? [duplicate]

Since Average acceleration is defined as, Average acceleration over a period of time is the change in Velocity divided by the Duration of the Period. Does Light (EM Wave) undergo acceleration during ...
2
votes
1answer
28 views

Distance from redshift

I am looking for a exact derivation of a relation between redshift $z$ and distance $d$. What I know is the definition ...
0
votes
2answers
77 views

Does a permanent magnet loose its magnetism?

The question is slightly deceiving however still simple for those academics therefore, here I present my question: If I take a para-magnetic material and put it very close to a homogeneous magnetic ...
0
votes
0answers
37 views

Resources for theory of distributions (Generalized functions) for physicists

I am looking for tutorials, articles or books containing theory of distributions in context of mathematical physics. Please suggest.
-3
votes
1answer
73 views

Does “dark matter” explain how I can have -1 apples? [on hold]

If I have 3 apples and you take 4 of them, that means I have -1 apples... is that apple made of dark matter?
2
votes
3answers
89 views

Where is the potential energy due to internal interactions in total energy?

In thermodynamics the total energy of a system consists of kinetic energy of motion of the system as a whole, potential energy of the system as a whole due to external force fields, and energy ...
1
vote
2answers
34 views

Why does the current increase in an LC circuit while the capacitor is being discharged?

From the maths governing an LC circuit (eg. $E_B=\frac{LI^2}{2}$) we can deduce, that the current through the inductor will have a maximum value, when there's no energy stored in the capacitor, or ...
0
votes
0answers
34 views

Non-unqiue basis sets of reduced density matrix in quantum mechanics/decoherence

In Why decoherence solves the measurement problem by Art Hobson: $|\psi \rangle _{SA} = c_1|s_1 \rangle |a_1 \rangle + c_2 |s_2\rangle |a_2 \rangle$ which is a wavefunction that describes non-local ...
-2
votes
0answers
26 views

Is it possible to record hand neural activity and use it to type? [on hold]

I hate keyboards and typing. But I have learned to type without looking. I know it's possible to detect which muscles are moving in the arm, hand, and finger. When you think about doing some action ...
1
vote
1answer
99 views

Subtlety in derivation of Noether's theorem by Di Francesco

In the book 'Conformal Field Theory' by Di Francesco et al, a derivation of Noether's theorem is demonstrated by imposing that, what I believe is said to be a more elegant approach, the parameter ...
2
votes
1answer
104 views

Why is the inertia ellipsoid of a higher symmetry than the rigid body?

I was always puzzled by this fact. A uniform cube has a sphere-shaped inertia ellipsoid. The sphere has a higher symmetry then the cube. Is there any deep reason or implication behind it?
-2
votes
0answers
24 views

problem: polarized sphere [on hold]

Need some help with a practice exam question: Given a solid sphere with radius R, with polarization density given by $P(\vec{r})) = a(R-r) \hat{z}$ . I need to find the potential inside the sphere, ...
1
vote
1answer
40 views

What force counteracts friction when a block is pulled?

Firstly, I understand and apologize that this is more of a physics question than a math question. I noticed that when I pulled a book out from under a pack of gum, the gum stayed largely in place (it ...
-1
votes
0answers
19 views

Preventing a train from derailing during turning by applying breaks from back to front [on hold]

My understanding regarding the derailing of trains during turning is that it occurs due to brakes being applied, from front to back, before the full length of the train has completed the turn which ...
4
votes
1answer
127 views

Does any lower frequency electromagnetic radiation naturally reach us from the Sun?

I am not sure whether the sun originally emits everything in the electromagnetic spectrum, (whatever the relative strengths of each portion might be), but I do read that many waves, including gamma / ...
-1
votes
0answers
24 views

Trying to calculate the average speed from this question [on hold]

I already checked the average speed question that was posted before and tried applying the methods to my question but nothing seemed to work. I would like to know if anyone can explain to me how to ...
-1
votes
3answers
65 views

Differences between wavefunction, probability and probability density?

I am trying to understand the differences between wavefunction, probability and probability density. There are different definitions on the internet. For example: ...
2
votes
2answers
81 views

Interpretation of a density matrix as an observable

In quantum mechanics, any density matrix (or density operator) is Hermitian. Observables are also represented by Hermitian operators. So it follows that a density matrix can also be interpreted as ...
2
votes
2answers
60 views

First-order and second-order wave equations, versus the uncertainty principle

In classical physics, we have second-order equations like Newton's laws, so we need to specify both position (zeroth order) and velocity (first order) of a particle as initial conditions, in order to ...
0
votes
0answers
16 views

Heat engine efficiency, compression ratio vs temperatures

I want to understand the role or even existence of a cold reservoir in the Otto cycle gasoline engine. The efficiency of the Otto engine is given as a function of compression ratio $$ ...
20
votes
3answers
1k views

The physical definition of work seems paradoxical

So this is possibly a misunderstanding of the meaning of work, but all the Physics texts, sites, and wiki that I've read don't clear this up for me: In the simplest case with the simplest statement, ...
-3
votes
0answers
39 views

What are quasars?

I was taught that apart from stars, the other self illuminating objects in the universe are quasars. What are quasars? It seems the definition of a quasar is an active galaxy? What is that and how ...
0
votes
0answers
19 views

Is it possible to go to graduate school in physics with a different undergrad degree? [on hold]

Specifically, a major in mathematics or applied math, while self studying the undergraduate physics curriculum, as I also want to major in computational biology. A triple major would make it difficult ...
1
vote
1answer
86 views

Why does a minor vertical vibration cause my coffee to spill?

When I walk my kid sometimes I put a cut of coffee in a cupholder attached to the stroller. When I push the stroller over a brick pavement it seems to vibrate vertically. That is enough for the coffee ...
1
vote
2answers
81 views

Action and Action integral: Different kinds of variational principles

What are the difference between: the action $\int_{t_{1}}^{t_{2}}(L+H) dt$ that we use in the principle of least action, and the action integral $\int_{t_{1}}^{t_{2}}L dt$ that we use in ...
1
vote
3answers
53 views

Basics of Current Electricity

I have certain questions which confuse me a great deal. I want to have a very basic and clear idea about some concepts. Here it goes: 1) I am really confused on how a battery actually works. The very ...
3
votes
0answers
46 views

Introductory derivations of Heisenberg uncertainty principle

I'm not an expert when it comes to quantum mechanics, so correct me wherever I'm wrong, but: I've always been a little bit bothered by introductory derivations of the Heisenberg uncertainty relations ...
3
votes
2answers
98 views

Why does blowing on hot coffee cool it down?

And will it cool off faster if you blow across the top of the cup or directly into the coffee? Does it have to do with the fact that when you blow across the top of the cup the velocity of the air ...
0
votes
0answers
9 views

How to survive a lightning strike [migrated]

Is this really a plausible way to survive a lightning strike ?
0
votes
0answers
21 views

Calculate Power requred to rotate a certain disk at a specific RPM in different conditions [on hold]

I have two acrylic disks with $x$ radius and $y$ thickness. I want to rotate that disk at certain RPM using a Motor. I know the weight of the disk. the weight of the Disks are virtually uniformly ...
5
votes
1answer
124 views
+50

Coleman-Weinberg potential: resum at 2 loops?

Say we want to compute the Coleman-Weinberg potential at 2 loops. The general strategy as we know is to expand the field $\phi$ around some background classical field $\phi \rightarrow \phi_b + ...
0
votes
0answers
24 views

Polarizable molecule in E-field

If we have a linear molecule with a dipole moment $\mu$ in a static electric field $E$, the potential is given by $V = - \langle \mu,E \rangle$. What is the appropriate equation for the potential if ...
1
vote
0answers
18 views

Energy conversion efficiency of Q-switched laser?

This is kind of an elementary question, but since i cannot find a reliable source on this i wanted to ask what is the formula for energy conversion efficiency? I know efficiency is calculated as ...
-1
votes
0answers
21 views

States that Wave-length, Pressure and Temperature describe [on hold]

I have two doubts : 1 - Can wave-length of light emited by some light-source ( like a black-body ) take arbitrary distance values ( any value in the set of real numbers ) ? 2 - Pressure is the name ...
1
vote
0answers
40 views

Confusion on entropy in the universe [on hold]

I was researching about the heat-death of the universe, and I was wondering if my understanding of it so far is factual to the theory? However, the 3rd Law of Thermodynamics prevents the universe’s ...
2
votes
2answers
38 views

Sound Wave out of phase

I connected my speakers to my sound system switching the +ve and -ve one of the speakers I can notice them beating out of phase but how come I don't hear any difference and at what position will it ...
1
vote
0answers
42 views

Are there any known (closed form even if approximate) solutions to problems in relativistic elasticity?

There are several useful known solutions to the EFE with relatively simple / trivial stress-energy-momentum tensor, such as the Schwarzschild solution. Despite the idealizations made therein they are ...
1
vote
0answers
74 views

Mathematical model that allows the existence of an infinite number of smallest, but different particles

Does there exist a mathematical formalism (model) in particle physics that assumes the existence of an infinite number of different, yet smallest particles (building blocks)?
13
votes
2answers
173 views

Physics of “boing” sound in raquetball courts?

While playing raquetball, I frequently hear a very prominent "boing" sound (or more formally, a chirp). For example, you can hear it in this video when the ball hits the front wall. Does anyone know ...
2
votes
1answer
55 views

Invariance of canonical Hamiltonian equation when adding the total time derivative of a function of $q_i$ and $t$ to the Lagrangian

The following is exercise 8.2 in 3rd edition (and exercise 8.19 in 2nd edition) of Goldstein's Classical Mechanics. Adding the total time derivative of a function of $q_i$ and t to the Lagrangian ...
0
votes
0answers
44 views

Mathematical formalism to include wave and particle perspectives of light

Does the exist any mathematical formalism (model) describing the behavior of light and incorporating its particle character (divisibility, quantization) and wave character? (i.e. quantized wave model) ...
0
votes
1answer
66 views

What exactly is a gauge anomaly?

In lots of papers I read about gauge anomalies. For example, avoiding gauge anamolies in the MSSM is the reason for introducing an extra Higgs doublet. Gauge anamolies in the Standard Model are ...
0
votes
3answers
35 views

Magnetic declination [on hold]

i couldnt just figure out when i got to know that declination can be zero also. How can true and magnetic north ever align themselves in a straight line in any place? Also if a compass aligns in the ...
-1
votes
1answer
14 views

Work to pump water through a hole in a trapezoidal prism

So I don't want to give the full details of the problem I'm working on, since I want to solve it myself. But I'm not sure which physical principles I'm supposed to use, since this is a Calc 2 ...
1
vote
1answer
29 views

Peaks and dips position in the Planck CMB

I am currently looking for the values of the firsts peaks and dips (at least the first 3) in terms of l and angular size for the CMB angular power spectrum measured from Planck. But the only thing I ...
2
votes
3answers
73 views

Is thermodynamic free energy and potential energy the same thing?

The equation for free energy $F$ and potential energy $E_{pot}$ are: $$ F=U-TS \\ E_{pot} = E_{tot} -E_{kin} $$ But the temperature $T$ is proportional to the average kinetic energy of a system. So ...

15 30 50 per page