All Questions
219,789
questions
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26
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Magnetic field strength beyond wire [closed]
If there is a point beyond a semi-infinite wire at a perpendicular distance r from it then what will be the magnetic field strength at the given point and what will be its direction?
0
votes
0
answers
10
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Mott dengerate semiconductor as absorber in solar cell
Does dengerate semiconductor—which met the Mott criterion—serve any purpose as an absorber for the photovoltaic effect in solar cell applications?
- 121
2
votes
0
answers
26
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Does a plasma with plasma frequency $\omega_p$ generate photons of the same frequency?
I know that photon emission in plasma results in a change of energy level of the electrons from excited or ionised atoms. However, I saw that photons of 13eV were created in a helium plasma, but this ...
- 21
0
votes
0
answers
68
views
How do you determine the electromotive force when the negative plate of the capacitor is connected to the positive terminal?
$\newcommand{\d}{\mathrm{d}}$We have a square wave source with period $T$ and voltage $V_0$ connected to a circuit which is has a resistor of resistance $R$ in series with an uncharged capacitor of ...
- 219
0
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0
answers
27
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How to take the average of a stochastic differential equation?
I am solving a set of stochastic differential equations and I need some feedback about if what I am doing is correct.
Given a vector $\boldsymbol{C}(t)=(C_+(t),C_-(t))^T$, we can writte a set of ...
- 13
-5
votes
0
answers
113
views
Criticising string theory [closed]
There are a number of pyhsicists claiming string theory has failed. Some facts: String theory did improve our understanding of quantum field theories in various dimensions and their interconnection ...
- 322
1
vote
0
answers
60
views
Lagrange multipliers not obeying classical EoMs
I will ask my question about Lagrange multipliers by using an example in string theory, as this question was inspired by my string theory course, but it applies to every theory with Lagrange ...
- 2,975
0
votes
0
answers
23
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Screening of the electric field by a grounded conductor in the presence of external charge
If we have an incompressible (constantly $\rho=const.$) charged fluid in some parts of space, this will trivially create some electric field.
Suppose we surround each of these domains of charged fluid ...
- 1
0
votes
1
answer
33
views
Quantum measurement in a strong magnetic field
I have a thought experiment that has been puzzling me regarding a spin-$\frac12$ particle placed in an extremely powerful magnetic field (say 1000 T for the sake of hyperbole) directed along the ...
- 636
1
vote
0
answers
35
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Does frequency affect current in Photoelectric effect? [duplicate]
If frequency of light in a photoelectric effect experiment increases (assuming its already enough to ionize the electrons), apparently the current will remain unaffected. This is contradictory to the ...
1
vote
1
answer
46
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Question in time period of oscillation of a ball in bowl [duplicate]
We know time period of pendulum is $$T=2\pi\sqrt{\frac{L}{g}}$$
While reading through a question on S.E which was based on a ball oscillating on a bowl , I was curious and I thought of its time period ...
- 472
0
votes
0
answers
13
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Why the broadening of coherence peak in superconducting spectrum is described by an imaginary term?
From Phys. Rev. Lett. 41 1509, the density of states of superconductor is
where iΓ is the broadening part.
Can anyone tell me why the broadening can be decribed by an imaginary part, what is its ...
- 13
2
votes
0
answers
32
views
What does the integral over the spectral function tell you physically?
I am playing around with some plots right now, and have some interesting looking results, but I am unsure how to read them. First, I am using the following real space BdG Hamiltonian:
$$ \hat{H}= -\...
- 351
-1
votes
0
answers
88
views
Why is SUSY algebra expressed as such?
In SUSY, many books describe its SUSY algebra like this.
$$\{Q_a, \bar Q_ \dot a\} = 2 \sigma ^\mu_{a \dot a} P_\mu,$$
and all other supercommutators vanish. But I don't understand why physicists ...
- 76
0
votes
0
answers
24
views
How would I solve the Helmholtz equation on a cross-sectional glass disk with many holes in the rod? [closed]
[rod with holes]1
Suppose you have an optical fiber rod with 19 holes as in the picture. The rod has a refractive index of 1.45, and the holes are assumed to have an index of 1. Can I use the ...
3
votes
0
answers
57
views
Dirac spinors vs. Wigner classification
As I understand, from Wigner's classification of particles it follows that for every $m > 0$ and $s \in \left\{ 0, \frac{1}{2}, 1, \frac{3}{2}, \dots \right\}$ there is an irreducible, unitary ...
- 914
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votes
1
answer
45
views
Can we say the momentum of a system is always equal to the momentum of the components of the system? [closed]
For ex if a ball of mass m undergoes an oscillatory motion in a bowl of mass M placed on planet where all surfaces are smooth( no friction ), while considering the part of the motion of the ball from ...
1
vote
0
answers
67
views
Why cant one-way speed of light be measured using a timer start that is electronically connected at midpoint? [duplicate]
Why can't one-way speed of light be measured using a timer start that is electronically connected at midpoint?
I'm sure I'm missing something, but why can't an experiment be built with two timers that ...
0
votes
0
answers
31
views
Mechanic Waves on a string . Formula not working [closed]
A sine wave with wavelength $\lambda$ moves along a string. Given the maximum transverse speed and maximum transverse acceleration, find the velocity of the wave $v$ and amplitude $A$ of the wave.
I'...
0
votes
5
answers
86
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Query in Newton's Third Law and friction
So My main question is about Friction in Newtons third law
Consider a box on the floor , A force $F$ is applied to it on the east direction , the floor then applies an equal and opposite force on the ...
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-3
votes
1
answer
70
views
The medium of electromagnetic waves [closed]
I'm just wondering if anyone else has ever pondered the question: what medium do electromagnetic waves travel through? and like me remained unsatisfied with the explanation that they are 'non-...
0
votes
1
answer
33
views
Coriolis force on a person on a carousel
Good afternoon all,
I am looking at the question Running backwards on a carousel from 2020 and the accepted answer given below it. Why is there no centripetal force on the person in either reference ...
- 57
0
votes
1
answer
48
views
Sampling random variable $x$ according to $f(x)$ [closed]
I am trying to sample the random variable $x$ that will follow a distribution given by
$$f(x) = A\exp{-x^{2}/B} ; x>0 $$
I generated $x$ with uniform distribution and used Acceptance-rejection ...
- 59
0
votes
0
answers
36
views
The flows of electrons when the voltage is zero [duplicate]
As we understand, electrons can't be unmoving therefore electrons always moving or flowing. If the voltage is zero, where do the electrons move? Do they move everywhere?
- 111
-1
votes
0
answers
19
views
How is trajectory prediction done on guided missile (which control systems for stabilization and changing trajectory) for application in Air defense? [closed]
I was just exploring ways to predict impact prediction of an incoming missile, I wanted to know how it is determined if a missile launched from a source point is detected by a radar will hit inside ...
- 19
0
votes
0
answers
32
views
Why is vacuum level continuous arcoss the system?
The answer to this question says
This is a static potential and thus has to be continuous. Otherwise energy conservation would be violated.
I don't find it satisfying.
How to define a "static ...
- 304
7
votes
4
answers
699
views
Confused regarding the wavelength of standing waves and their relation with wave speed
Suppose we have an air column closed at one end and open at one end. We know, the general formula for the wavelength of the stationary waves of different harmonics will be equal to $4L/n$. My ...
- 95
0
votes
0
answers
15
views
Estimating dielectric polarization based on supply voltage frequency [closed]
I am currently dealing with a problem which has a series of conductors (assume them to be copper) embedded in a film made of a polyimide material and the film is exposed to air. The conductors are ...
0
votes
2
answers
46
views
Is the observed speed of an infinite set of perfect ocean waves of constant amplitude and frequency independent of an observer's motion?
I am asking this question because it occurred to me that wave propagation has some generally under considered properties regardless and independent of the medium in which the waves are propagating. ...
-1
votes
0
answers
18
views
Can you tell about Nucleus mass defect according to reference of proton having sea of quarks [closed]
Related with particalphysics and also chromo quantum dynamics please tell the suitable answer
0
votes
1
answer
76
views
What if atom receives energy higher than $\Delta_1$ but lower than$\Delta_2$? [duplicate]
Considering an atom at ground state 0.
To be excited to state 1, it needs to get, as understand $E_e = E_0 - E_1$.
What if, atom at $E_0$ interacts with photon, which energy is higher than $E_0 - E_1$,...
- 297
2
votes
2
answers
140
views
Is linear momentum quantized in quantum harmonic oscillator
I'm self-studying QM and have a basic question on quantum harmonic oscillator. The Hamilton is certainly quantized under this model, that is $E_n=(n+1/2)\hbar \omega$, for $n=0,1,2,...$. But is linear ...
- 41
1
vote
1
answer
17
views
Isolator resistance on external radiation dependency
Considering a silicon (but also any isolator), that has band gap $E_g = 1.12 eV$ at $T = 300K$, do I understand correctly, that by shining on just a piece of silicon with at least infrared radiation ($...
- 297
1
vote
1
answer
58
views
Is cosmological expansion paradoxical?
Suppose that there are three points in space. The distance between any two of the closest points is less than or equal to the cosmological horizon. Such is the case that information cannot be ...
- 237
0
votes
1
answer
16
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Magnetization Enhancement Using Various Materials
I was looking online at how inserting a material inside a solenoid can enhance/reduce the magnitude of a magnetic field in all space depending on what material is inserted. This makes sense from a ...
- 25
0
votes
1
answer
31
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Confusion regarding net acceleration of the bob in the bottommost point of the trajectory of a pendulum? [closed]
Here is my analysis from the inertial frame on it:
At the bottom most point,
$g$ acting downwards
$v^2/r$ (centripetal acceleration) acting upwards
So the net acceleration, a = $(v^2/r)-g$ right?
...
6
votes
3
answers
749
views
How does the absence of quadratic terms in the Lagrangian imply massless quanta?
When studying gauge theory, I often see the statement that gauge invariance does not allow the Lagrangian of the theory to contain terms that are quadratic in the gauge field. For example, to quote ...
- 1,890
0
votes
1
answer
40
views
Problem figuring out correct sign using newton's third law [closed]
I'm having trouble interpreting Newton's third law on a block classic problem.
Considering a constant horizontal force acting on two blocks of masses $m_A$ and $m_B$ must give an acceleration of $a = \...
- 3
1
vote
0
answers
31
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Can oxygen 'leach' along a wire?
[If this is not the right SE for this question, apologies.]
Automobile gasoline engine controls use oxygen sensors in the exhaust stream. The Wikipedia article on Oxygen Sensors notes that (some) ...
- 111
8
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0
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91
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+100
What are the exact relations between bound states, discrete spectra, and negative energies in quantum mechanics?
Consider the nonrelativistic quantum mechanics of one particle in one dimension ("NRQMOPOD") with the time-independent Schrodinger equation
$$
\left( -\frac{\hbar^2}{2m} \frac{d^2}{dx^2} + V(...
- 45.1k
0
votes
0
answers
16
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Necking stage in bubble detachment
The first image is the bubble dynamics in nucleate boiling, in a) you can see that the bubble is detaching by minimizing contact line with surface until zero, while in b) the bubble is enlongate and ...
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0
answers
20
views
Magnetic pressure explanation and penetration depths
Can I get an explanation of what magnetic pressure is exactly in the context of MHD? From my simple understand, it's essentially just the force that magnetic field lines exert back onto a plasma that ...
- 25
1
vote
1
answer
42
views
Perturbative non-renormalizability and viability?
Does perturbative non-renormalizability indicate the unviability of the theory if we were to define it non-perturbatively (for example through a lattice discretization of the continuum QFT or other ...
- 699
0
votes
1
answer
33
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Semiconductor conductivity increases but Fermi level decreases
I was going through this question:
Why does the Fermi-level decrease with temperature increase?
As the temperature increases though the semiconductor becomes intrinsic where number of holes equals ...
- 679
0
votes
0
answers
34
views
Current in a cube resistor [closed]
I am given this cube of resistors, each with the same resistance of 4 Ω. The current that enters at E and leaves B is 6 A. I have found that the equivalent resistance is 3 Ω. However, I am unsure of ...
- 59
0
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0
answers
23
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Understanding the physics of a vertical axis wind turbine
I have a physics background, but not much aerospace. I'm attempting to understand the operating principal of a vertical axis wind turbine. I've found a paper with a free body diagram, which I mostly ...
- 113
1
vote
1
answer
107
views
+50
Transformation of basis vector in Kruskal coordinate
For Schwarzschild solution:
$\mathrm{d} s^2=\left(1-\frac{2m}{r}\right)dt^2 - \left(1-\frac{2m}{r}\right)^{-1}\mathrm{d} r^2-r^2(\mathrm{d}\theta^2+sin^2\theta \mathrm{d}\phi^2),$
Introduce tortoise ...
- 337
-1
votes
1
answer
29
views
Ground states of an Hamiltonian in Statistical Mechanics [closed]
I had a general question in statistical mechanics. If we're given a certain Hamiltonian and we're asked to draw its zero-temperature phase diagram can we equal the energy to free energy. And if we ...
0
votes
0
answers
16
views
Charge on a conducting sphere inside uniform electric field after it is ungrounded [closed]
A grounded conducting sphere of radius R is immersed in a uniform vertical electric field E on the z axis. The electric field induces a distribution of charges on the sphere. What is the net charge Q ...
- 1
2
votes
1
answer
24
views
Modelling the Sound of a Gun's Smokeless Powder Explosion
I am seeking to synthesize the sound of a gunshot.
I am aware the firing of a gun is made up of many parts, but I would like to handle the explosion of smokeless powder in the bore first.
Here's what ...
- 21