# All Questions

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### Are source and sink part of system or are they part of the surroundings? [closed]

Are source and sink part of the system or are they part of the surroundings?
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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 ...
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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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### 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 ...
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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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### How fast is the naked-eye visible transition of a main sequence star to a giant?

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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### 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 ...
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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 ...
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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 ...
1 vote
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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 ...
1 vote
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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)

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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### 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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### 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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### 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 ...
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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 $W=-\... 0 votes 1 answer 26 views ### Unique distribution of charge on a conductor If i place some charge on a conductor then it will distribute itself in such a way that electric field everywhere inside is zero. My text book says that only one kind of such charge distribution is ... 0 votes 1 answer 40 views ### My book states that contact force between two surface is equal to$\sqrt{N^2+F^2}$. where$N$is the normal force and$F$is the friction Applied Force is our label for a contact force that a person exerts. When an applied force acts at an angle, it is actually a combination of two forces: normal and friction. The component of the ... 0 votes 1 answer 40 views ### Understanding Double slit and delayed choice experiment I am having some trouble with two thought experiments, so I will list both of them below and I would be most grateful If somebody could explain to me what is actually going on or where I went wrong (... 2 votes 2 answers 60 views ### When we solve the Maxwell equations for$(\phi,{\bf A})$in a gauge, will the solution$(\phi,{\bf A})$automatically obey the gauge condition? As the title of the question suggest; how you could determine if a gauge fixing is a condition or a requirement. Let me explain. Imagine you are working with Maxwell's Equations. By the definition of ... 0 votes 0 answers 13 views ### What is a symmetry defect? I found that it is a normal concept appearing in condensed matter physics and especially topological order field. I have been aware of the topological defect. But what is a symmetry defect? Could ... 0 votes 1 answer 33 views ### Confusion about energy transport in a circuit I have some confusions about how to imagine energy flow in a circuit. Imagine for example just a simple circuit with a battery, two wires and a light bulb. According to classical Electrodynamics the ... 0 votes 1 answer 43 views ### What are some ways to derive$\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}... 0 votes 0 answers 26 views ### 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 \... 0 votes 0 answers 21 views ### 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? 1 vote 0 answers 20 views ### 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 ... -6 votes 0 answers 53 views ### Thermodynamic Bounds on Quantum Computing [closed] Disclaimer: To keep this post from getting cluttered with poor-quality comments, I ask that only experts on the subject provide answers or comments. You must understand the physical assumptions behind ... 1 vote 0 answers 37 views ### 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 ... 0 votes 0 answers 12 views ### 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 ... -1 votes 0 answers 26 views ### 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 ... 1 vote 0 answers 31 views ### Vector bilinear on AdS manifold If I have a manifold with the following metric (where \hat a are the flat indices)$$ dS^2_D = \eta_{\hat a\hat b}e^{\hat a}e^{\hat b} = L^2\Big(\frac{du^2}{u^2} + u^2\eta_{\mu\nu}dx^\mu dx^\nu\Big) ... 0 votes 0 answers 16 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 ... 1 vote 0 answers 11 views ### 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 ... 0 votes 1 answer 55 views ### 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 ... 0 votes 1 answer 52 views ### 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 ... 0 votes 0 answers 18 views ### 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 views ### 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). ... 0 votes 2 answers 45 views ### How do we solve polar coordinates related questions? A particle is subjected to a radial force:$\vec{F}=f(\vec{|r|}) \hat{e_r}$. How do we show that$\vec{F}×\vec{L}=-mf(r)[-\vec{r}\dot r+r \dot {\vec{r}}]$1 vote 0 answers 35 views ### Why assume no degeneracy in Spin operator? The Stern-Gerlach experiment measures a physical property of a quantum system. We hence associate an operator$\hat{S_z}$with the observable, in accodance with the postulates of QM. The eigenvalues ... 0 votes 0 answers 26 views ### Quantum many body physics - Superconductivity [closed] why propagation of hole in Green function is backward in time not forward? -1 votes 0 answers 10 views ### Coupled Resonators with sinusoidal coupling [closed] I have two coupled resonators with complex resonance frequencies of$\beta_1$and$\beta_2$. The coupling between them is varying sinusoidal with time. The time-evolution of their resonant mode field (... 0 votes 0 answers 48 views ###${}\$Higgs mechanism

Is is correct to say that, elementary particles have different masses, because they have different coupling strengths to Higgs field? And if yes. Does it make sense to question, why they have ...
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### How did sample answer get theta2=-60 when in the question itself it is given to you as 30 degrees. How did they get-60 degrees? [closed]

I gave full clarification with 3 images. Two of those images highlighted in red are the doubt/question. I do not understand how the answer was cos(-60) when it is meant to be cos(30). I do not ...
1 vote
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### Does positive-definite Hamiltonian for a fermion make sense?

I have been told that positive-definite Hamiltonian for a fermion doesn't make sense. Can anyone explain why is that the case?