All Questions
227,232
questions
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Solution as the real part of complex exponential for simple harmonic motion
Reading through the "Solution as the real part of complex exponential" section of the John Taylor textbook on classical mechanics, I noticed the following :
$x(t) = C_{1}e^{i\omega t} + C_{1}...
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-3
votes
0
answers
41
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Isn't Gravity at least "sort of" predicted by QFT? [closed]
Let me say to begin with that I'm not a crackpot and don't think I've discovered anything new here. I'm a physics graduate student but not in quantum gravity but I still like the idea of unification ...
- 169
-2
votes
2
answers
50
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What differs temperature from the mean kinetic energy of a particle?
The mean kinetic energy of a particle for an ideal gas is related to temperature by:
$$ KE = \frac{3}{2} k T \tag{1} $$
My question is why $KE \neq T$. To me it seems a far simpler relationship if ...
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-1
votes
1
answer
21
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Density of states for fermions - Statistical Mechanics
I'm studying about the density of states $g(k)$ of fermions at the moment and its equations, but I'm confused about the following:
This is an equation given in the notes for the course, where $N$ is ...
- 35
0
votes
1
answer
54
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How to correctly use Gauss Law? Why is it used the way it is?
Gauss Law
$$\oint \vec E . d \vec A = \frac{Q_{enclosed}}{\epsilon _○}$$ From this question, Gauss Law is more fundamental than Coulomb's Law. This seems counter intuitive to me when it comes to ...
- 107
2
votes
1
answer
17
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How can I identify momentum eigenstates in a tight binding model with degenerate energy eigenstates?
Summary:
I numerically diagonalize a tight binding Hamiltonian to get energy eigenvectors, some of which are degenerate. However, the numerically diagonalized degenerate eigenvectors are not ...
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0
answers
31
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Can 3 objects with same mass dropped from 10,000ft land in the same region/area together? [closed]
I mean specifically VERY close together, like in the same spot next to each other? And specifically, for example, objects such as 3 separate elastic band-bound bundles of €20 bills amounting to €2,000 ...
-1
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0
answers
26
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Galilean invariance of the potential [closed]
The first problem on my exercise sheet is about the galilean invariance and im stuck there. So the Problem is:
We consider a system of n particles, described by the following galilean invariant law ...
- 1
0
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0
answers
12
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Atmospheric refraction - large distances
In the webpage here Mirages and other atomospheric optic phenomena (gsu.edu) it says the atmospheric refraction can project images for very large distances. How many kilometers could be those very ...
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1
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0
answers
22
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Lenz's law in supercoductors: What happens if a superconducting ring approaches a bar magnet?
Assume that the alignment of a bar magnet passes through the center of a superconducting ring. Can we say that if we accelerate the ring toward a pole of the bar magnet applying a force $F$, the ...
- 2,455
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0
answers
24
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Are source and sink part of system or are they part of the surroundings?
This question is regarding the interactions of a thermodynamic system with its environment: do we count the sources and sinks of entropy (heat) as part of the thermodynamic system or as part of the ...
-4
votes
1
answer
49
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What's the speed limit for things with mass?
So the speed limit of the universe is 299 792 458 m/s, but only massless things like photons can archieve this speed. Since things that have mass can reach 99.99999...% speed of light, does that mean ...
1
vote
2
answers
51
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The difference in path lengths for waves in the double slit experiment
Fig.1
I don't quite understand the diagram, because it shows $L_1$ and $L_2$ as parallel, even though they are supposed to meet at the same point. I believe the idea is that $\Delta L$ approaches $d \...
- 236
1
vote
1
answer
110
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Why rocket equation? [closed]
while deriving rocket equation we find change in momentum of rocket
and this is the result:
$$Δp=MΔV+Ve ΔM$$
from here we divide this by time to calculate force and since no external force(freespace) ...
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votes
0
answers
57
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If acceleration is a function of time like this $a=mt²$ where $m$ is constant. Then must be $v = a×t = mt³$ [closed]
Actually v is equal (at³)/3 by integration
But why v can not be equal to at³
-3
votes
2
answers
63
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Definitions of Thermodynamics and Holography
There are many differences between the laws of thermodynamics and the laws of black hole thermodynamics (BHT):
Zeroth Law: In thermodynamics, the Zeroth Law establishes the notion of thermal ...
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votes
0
answers
45
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Confusion between the contact force in string
My textbook says that when two bodies are in contact there exist a contact force between them and it has two components also one is perpendicular to the surface and the other is parallel to the ...
0
votes
0
answers
23
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The Spin of a Single EPR Particle
Here's my understanding of spin in cases of superposition and entanglement
1. In a case of superposition
Suppose an electron is in a superposition of two spin eigenstates along the $i$-axis, $|1\...
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votes
0
answers
15
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Can u tell whether Acceleration of point contact is correct or not for rolling with slipping (backward slipping)? [closed]
Rolling with slipping backward
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votes
1
answer
26
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Correct frame for angular velocity in quaternion's kinematic
I am reading a paper where the quaternion's kinematic is used, unfortunately the description of the angular velocity does not match with how it's computed, so I have a doubt on which frame $\omega$ is ...
-2
votes
1
answer
80
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How can Electricity travel at the speed of light?
If electricity is the flow of electrons, how come it can flow at the speed of light? Shouldn't how fast it moves be limited to a speed lower than the speed of light because it has mass?
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0
answers
16
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How fast is the naked-eye visible transition of a main sequence star to a giant? [duplicate]
I know the evolution of a main sequence star to a giant is a process that takes millions and millions of years, but how fast is the VISIBLE change? Basically, will our sun, for example, slowly grow to ...
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0
answers
29
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Solving Time Dependent Schrödinger's Equation in Rotating Frame
My Hamiltonian is: $\frac{1}{\hbar}\hat{H}=\frac{1}{2}\Delta \hat{\sigma _z} + \frac{1}{2}\epsilon _d \hat{\sigma _x}$ where $\Delta$ is a constant made of frequencies.
I need to solve my TDSE ...
- 143
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0
answers
19
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Explain this step (related to gamma matrices and parity operator)
I am having hard time reproducing a step from the textbook "Lecture Notes on Quantum Field Theory", by Ashok Das. On page 429 ( above equation 11.72), the author is talking about the parity ...
- 291
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votes
1
answer
59
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Confusion about Deriving Momentum Operator and Hamiltonian Operator
In Sakurai's quantum mechanics, the derivation of momentum operator and Hamlitonian operator is based on spatial translation and time translation as below,
for spatial translation and momentum ...
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1
vote
1
answer
25
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Canonical and kinetic momenta vs gauge dependence
I am struggling a bit to understand the concept of gauge invariance/dependence with canonical momentum.
For instance, if we consider a Hamiltonian of a particle in an electromagnetic field described ...
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0
votes
5
answers
133
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I am confused in work-energy theorem, Why the ball doesn't go to the same height from which it fall down? (sorry if my grammer isn't correct) [closed]
Here's the figure, ball fall from height of 2 m (at point A)
But reaches the height of 1m at point P
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0
answers
15
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Which statistical methods are better than basic random scans for studying and exploring the parameter space of extensions of the standard model?
Given a lagrangian of a new model beyond the standard model, and given a set of constraints, say the oblique parameters for instance and the decay of the higgs boson and some signal strengths and ...
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0
votes
0
answers
27
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Use of sign convention two times in ray optics
In this particular derivation of refraction happening at a spherical surface in terms of its radius of curvature , image and object distance and refractive index is done by my book as shown
When we ...
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votes
1
answer
47
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Probability and Thermodynamics: Analysing feasibility of 50 benches problem
Question:
I have a thought experiment that involves dropping 50 benches from a height through an open roof and examining the probability of them spontaneously arranging themselves into neat rows and ...
0
votes
1
answer
28
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Work done by adiabatic expansion derivation
I know that $W=-C_v(T_2-T_1)$ for an adiabatic expansion, and I know how to derive it. However, in this video (https://youtu.be/gaZmZjBtgAM?si=Px3v2qDG3CIdupgi&t=358) it mentions the formula $W=-\...
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votes
1
answer
41
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Unique distribution of charge on a conductor
If i place some charge on a conductor then it will distribute itself in such a way that electric field everywhere inside is zero. My text book says that only one kind of such charge distribution is ...
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votes
1
answer
40
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My book states that contact force between two surface is equal to $\sqrt{N^2+F^2}$. where $N$ is the normal force and $F$ is the friction
Applied Force is our label for a contact force that a person exerts. When an applied force acts at an angle, it is actually a combination of two forces: normal and friction. The component of the ...
- 1
0
votes
1
answer
46
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Understanding Double slit and delayed choice experiment
I am having some trouble with two thought experiments, so I will list both of them below and I would be most grateful If somebody could explain to me what is actually going on or where I went wrong (...
2
votes
2
answers
69
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When we solve the Maxwell equations for $(\phi,{\bf A})$ in a gauge, will the solution $(\phi,{\bf A})$ automatically obey the gauge condition?
As the title of the question suggest; how you could determine if a gauge fixing is a condition or a requirement. Let me explain.
Imagine you are working with Maxwell's Equations. By the definition of ...
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0
answers
15
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What is a symmetry defect?
I found that it is a normal concept appearing in condensed matter physics and especially topological order field. I have been aware of the topological defect. But what is a symmetry defect? Could ...
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votes
1
answer
39
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Confusion about energy transport in a circuit
I have some confusions about how to imagine energy flow in a circuit. Imagine for example just a simple circuit with a battery, two wires and a light bulb.
According to classical Electrodynamics the ...
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votes
1
answer
48
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What are some ways to derive $\left( \boldsymbol{E}\cdot \boldsymbol{E} \right) \nabla =\frac{1}{2}\nabla \boldsymbol{E}^2$?
For each of the two reference books the constant equations are as follows:
$$
\boldsymbol{E}\times \left( \nabla \times \boldsymbol{E} \right) =-\left( \boldsymbol{E}\cdot \nabla \right) \boldsymbol{E}...
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0
answers
30
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The magnetic force is conservative when the magnetic field is static, what is its potential function then?
The magnetic force $\vec{F}$ can be conservative when the magnetic field is a static. That is $\vec{\nabla} \times \vec{F}=0$, so it follows that there is a scalar function $f$ such that $\vec{F}=q \...
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0
answers
21
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Constraint relations problem (High school physics) [closed]
I have solved similar problems by relating their displacements and differentiating with respect to time to find their velocities, but how do I solve this?
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0
answers
38
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Is there any measurement of all the observable angular momentum in the Universe?
Has the sum of all observable angular momentum in the Universe ever been evaluated? There has been a lot of efforts dedicated to the missing mass and energy problem, but has any experimental work ever ...
- 1,787
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0
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39
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What contributes most to the mass of the proton?
i'm a bit confused about the origin of the mass of the proton (or other hadrons). It is said that it stems from the renormalization of the current quarks, which have about 1/100 of the mass of the ...
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0
answers
15
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Hamiltonian analysis of relational $N$-Particle Dynamics
I am following "A Shape Dynamics Tutorial, Flavio Mercati" (https://arxiv.org/abs/1409.0105), and have problems understanding the hamiltonian formulation of $N$-particle dynamics as sketched ...
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0
answers
27
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Finding unknown resistance in Wheatstone bridge [closed]
Here's a question of NEET:
A Wheatstone bridge is used to determine the value of unknown resistance X by adjusting the variable resistance Y as shown in the figure. For the most precise measurement ...
0
votes
0
answers
17
views
Probability density of an accelerating charge?
Is the probability density of an accelerating charge in free-space spherically-symmetric? If not, is it possible to produce charge acceleration-induced short range oscillations of charge probability ...
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1
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0
answers
12
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Temperature Estimation for Insulated Bottom Surface in Water Cooling
In a 2D plane heat flux q'' is incident on an insulation layer (which has a thickness L and a thermal conductivity k). The bottom surface of this insulation layer is exposed to water cooling with a ...
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1
answer
57
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What are some examples of bounded momentum/Hamiltonian operators in infinite dimensional Hilbert spaces?
It is well known that one of the operators satisfying the Canonical Commutation Relation $[x,p]=i$ must be unbounded. In most cases I have seen, either both are unbounded or only $p$ is (e.g. Particle ...
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1
answer
53
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Expression of Bianchi identity in associated bundle
Theorem 5.14.2 of Mathematical Gauge Theory by Hamilton states that the curvature form $F^A_M\in\Omega^2(M,Ad(P))$ satisfies the third form of the Bianchi identity $d_AF^A_M=0$ where $F^A_M$ is the ...
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0
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19
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Struggling with physics homework, how do I find the acceleration of the system? [closed]
A 600 kg helicopter flies straight upward with a lift force of 12,000 N. A 150-kg spy named 007 hangs onto rope that is connected to the helocopter. A 50 kg physics student hangs onto a second rope ...
0
votes
1
answer
20
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Will hot object near ceiling vent create more draft? [closed]
As in the picture, we have a room with vents at the bottom to let cold air in and at the top to let hot air out. Normally the air flow is limited by the temperature gradient (correct me if I'm wrong). ...
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