All Questions

3
votes
1answer
52 views

Entanglement breaking quantum channels

An entanglement breaking quantum channel is defined as one where $\sigma_{AB}=(\Phi_A\otimes I_B)(\rho_{AB})$ is separable, even for entangled inputs $\rho_{AB}$. Of course, if the input $\rho_{AB}$ ...
0
votes
0answers
12 views

Bernoulli's equation: distributing energy per unit volume into static pressure vs. dynamic pressure

In any fluids problem solvable using Bernoulli's equation, the question always seems to assume initial values of static pressure ($P$) vs. dynamic pressure ($1/2\rho v^2$). In the initial setup of a ...
0
votes
1answer
21 views

Calculating refractionindex of water given permittivity

I'm a bit confused. The refraction index is calculated by $$n=\frac{c}{v},\tag1$$ where $c$ is the lightspeed and $v$ is the phasevelocity of light in the medium of interest, water in this case. In ...
0
votes
0answers
32 views

Somehow unexisting book even though volume 2 exists

I am desperately trying to find a book Electromagnetic Interactions of Hadrons, Vol.1, A Donnachie; G Shaw; New York 1978 Somehow, the second volume is easily ...
3
votes
1answer
55 views

Why Aren't Hadron Masses More Useful In Determining Standard Model Constant Values?

Some of the most exquisitely precise experimental measurements in all of physics are the masses of the various hadrons. Consider these examples: the proton mass is known to eleven significant digits. ...
1
vote
3answers
44 views

If an electric field passing through a dielectric medium, back into the original medium, is it “back to normal”?

Suppose there is an electric point charge causing an electric field E in a medium with a dielectric constant $\epsilon_1$. You can calculate the scalar potential $\phi$ at a given distance $r$, as ...
3
votes
1answer
285 views

Show two Lagrangians are equivalent

I need to show that these two Lagrangians are equivalent: \begin{align} L(\dot{x},\dot{y},x,y)&=\dot x^2+\dot y + x^2-y ,\\ \tilde{L}(\dot x, \dot y, x, y)&=\dot x^2+\dot y -2y^3. \end{align} ...
2
votes
1answer
63 views

Does it make sense to speak in a total derivative of a functional? Part III

In this third part of the series, I will continue the deduction of Noether's theorem initiated in the previous post - Does it make sense to speak in a total derivative of a functional? Part II. ...
0
votes
0answers
34 views

Insufficiency of Newton's third law to solve constrained motion problems

In The Variational Principles of Mechanics Lanczos describes what he calls 'vectorial mechanics': the process of solving mechanical problems by recourse to the immediate consequences of Newton's laws, ...
1
vote
2answers
73 views

Why there are 3 significant figures in 86400 but 5 in 86400 s ( because of Unit)

My book states one rule for determining the number of significant figures as under: All zeroes to the right of a non zero digit but to the left of an understood decimal point are not significant . ...
0
votes
0answers
27 views

Canonical and grand canonical formalism at zero temperature

How do we find expectation value of any operator at zero temperature in quantum statistical mechanics formalism? Expectation value of any operator $\hat{O}$ is given as $$\langle \hat{O}\rangle = Z^{-...
0
votes
0answers
33 views

Moment of intertia of a trinagle pendulum [on hold]

Find the moment of inertia of 3 rods with mass m and length L connected to form a triangle. The axis of rotation is that of a pendulum. The moment of inertia of a single rod with the axis through its ...
3
votes
1answer
47 views

Are theta vacua topologically protected?

In discussions of Yang-Mills instantons it is often stated that one should sum in the path integral over all contributions of fluctuations around all the topologically distinct vacua labelled by ...
-1
votes
0answers
15 views

Do you know answer(solution) about this question? for evaporation, thin film deposition [on hold]

Evaporation 7) For Al evaporating at 1100oC, vH = 318 kJ/mole. Assuming atomic vapor, what fraction of this energy goes into pV, what fraction into kinetic energy, and what fraction into potential ...
3
votes
0answers
62 views

Method to build a polyhedral dice with given probabilities [on hold]

Let's define a dice as a polyhedron that, if rolled over a perfect horizontal plane, ends up being in a physically stable unambiguous state labelled $n$. The dice has $N$ states. Each state $n$ has a ...
-1
votes
1answer
27 views

Why succeptibility diverges towards Tc in second order phase transition? [on hold]

Second order phase transition image as shown below.
0
votes
1answer
62 views

QFT must vacuum states have non zero energy?

Vacuum states of different quantum fields corresponds to different energy levels. Some sources say they are mostly zero, some other says that it is a limit imposed by heisenberg uncertainty principle, ...
0
votes
0answers
15 views

What happens to the heavy elements when a gas giant with no core or one with metallic hydrogen is formed?

I have been trying to visualize how a gas giant like Jupiter originally formed. I am assuming that in its early stages it formed by aggregation similar to how the rocky inner planets were with an ...
-3
votes
0answers
29 views

How to dock a rocket to the ISS? [on hold]

A supply rocket, with its engines, shut down, is trying to dock with the ISS. Initially, it is moving in the same circular orbit above the earth and the same speed as the ISS. The two craft are ...
1
vote
0answers
30 views

CP violation measurement

I have a question regarding the measurement of CP Violation in experiment. How is parity measured in an experiment? I know that in the direct measurement of CP violation we look at a particle process ...
0
votes
0answers
21 views

Finding number of photons per second crossing an area with distance ${}d$ from a radiating point [on hold]

Estimate the number of photon per second entering one eye of the observer from 10 Watt red light source at 50m away form point source.
0
votes
1answer
42 views

Speed of light dependent on source velocity in other medium [duplicate]

Does speed of light depends upon the velocity of source in a medium (like water) other than space? if yes, does the speed gets added up when the light source moves in direction of light?
3
votes
0answers
32 views

Electrostatic force setup not working

I am using a glass rod and a polythene bag for a demonstration on electrostatic force. The setup was working perfectly fine yesterday night and I could attract small pieces of paper and I verified it ...
1
vote
0answers
33 views

Second order relativistic corrections to Pauli equation from Dirac equation

I'm trying to derive the full and correct Hamiltonian for spin$\frac{1}{2}$ particles from Dirac equation up to second order in $v/c$. For a potential and magnetic field constant in time. In ...
0
votes
1answer
43 views

Is curvature the exterior covariant derivative of the connection?

Let $P\to M$ be a $G$-principal bundle, $G$ a topological group, $\omega$ the connection and $V$ a vector space. We define $d_\omega: \Omega^k_G(P, V)\to\Omega^{k+1}_G(P, V)$ the exterior covariant ...
3
votes
3answers
111 views

Which place in the universe that does not have force at all

Does a place without force exsist, if it so where or how could it be. I mean if we include Gravity and friction as our force in universe.
3
votes
0answers
48 views

Conservation of $\int |\psi|^2$ for Dirac wave

When $\psi$ be Schrodinger wave $\int |\psi|^2$ is conserved even when this wave interact whit another wave say electromagnetic wave. and this is very necessary for one particle interpretation of this ...
3
votes
1answer
89 views

How to interpret phase diagrams?

I find quite difficult to interpret phase diagrams in general, for example I see people discuss them along the following lines: Here we see the coexistence line between liquid-solid phases.. a ...
1
vote
0answers
20 views

BKT transition: nature of topological transition

BKT-transition is one of the most well-known topological transition in $O(2)$ model.But I misunderstand the physical interpratation of this transition. I started from the low-temperature expansion of ...
0
votes
1answer
61 views

How to efficiently compute the commutator $[\hat{r},\nabla^2]$?

Given a system with Hamiltonian $ \hat{H} = \frac {\hat{p} ^2}{2m} + \hat{V}(r)$ in a certain state $|\psi \rangle$, I want to find if $\langle r \rangle$ varies with time. From $$ i \hbar\frac {d ...
0
votes
2answers
55 views

Spaceship A and Spaceship B move in opposite directions at half the speed of light, and A fires a laser at B, does the laser light reach Spaceship B? [on hold]

This question has been bugging me for a week now! I believe it would, but logically, I feel like I'm missing something. Please give a full explanation.
1
vote
1answer
30 views

Reciprocal lattice points and diffraction peaks

I am having a issue with the concept of what this question is asking. Question For a FCC crystal describe all the reciprocal lattice points corresponding to the two diffraction peaks. Here is my ...
0
votes
1answer
34 views

Conventions in the FRW metric

So the FRW metric is $$ds^2=-c^2dt^2+a(t)^2\left(\frac{dr^2}{1-kr^2}+r^2(d\theta^2+\sin^2\theta d\phi^2)\right). $$ I have seen books mention that $k=1,0,-1$ - depending one of the values listed ...
3
votes
0answers
26 views

How can compact fluoscent lamps light up?

My understanding of fluorescent tubes is that filament on one side gets very hot, undergoes thermoionisation and shoots electrons into the gas. The collision between a mercury gas atom and a fast ...
1
vote
0answers
15 views

Why does friction occur? [duplicate]

I'm pretty sure this is a rather stupid question but I just cannot wrap my mind around the reasoning behind friction. Now, an obvious explanation would be that since all surfaces are inherently rough,...
1
vote
1answer
25 views

Inertial frames with unknown past

Let's suppose two ships that cross in space at constant speed. We do not know their previous acceleration or velocity history. When they cross, they synchronize watches. From that moment, if they ...
0
votes
0answers
20 views

Muon capture cross-section

I would like to understand how the cross-section of muon capture depends on the nuclear charge. My attempts are based on the following thinking. Muon is captured to "high" orbital and then muon goes ...
0
votes
0answers
6 views

Why are rockets with High specific impulse not used for transferring satellites?

I believe one reason could be that high Specific impulse rockets would take longer time to reach the orbit. Is higher time the only reason for using rockets with low specific impulses like Falcon 9 ...
0
votes
3answers
42 views

Is external force equal to restoring force [duplicate]

I have reached a confusion. We know $$F=-kx$$ in a spring. If an external mass $m$ is suspended to a spring and the spring extends by a length $x$ and the mass comes to rest, external force, $~mg = \...
0
votes
1answer
62 views

In QM does the observer really perturb the system to make a measurement?

It is commonly taught in introductory QM courses that in order to get to know the position or momentum of a particle, be it by "sending a photon" or similar experiments, the measurement necessarily ...
1
vote
0answers
29 views

Casimir effect: where did the pressure come from?

From my understanding of Casimir effect, there exists a difference in energy between plates and that of the outside environment. How did this translate to a pressure difference and eventually where ...
0
votes
0answers
32 views

Saha-Boltzmann Equation

I am following Ahmed, Ahmed, Rafiqe & Baig A comparative study of Cu–Ni Alloy using LIBS, LA-TOF, EDX, and XRF paper on Laser Induced Breakdown spectroscopy. It mentions two versions of Saha-...
2
votes
1answer
71 views

What's the definition of repulsive gravity?

After asking this question, I got confused. I always thought that repulsive gravity was a consequence of dark energy, the Nature of which is unknown. Many theories are flying around about its Nature. ...
0
votes
1answer
20 views

How does charge develop inside a spherical shell (with non-negligible thickness)?

I read that if there were a charge $+q \ $ kept inside a spherical conducting shell of thickness $t$, a charge of $-q \ $ would develop on the inner surface of the shell. Not more, not less. Why is ...
3
votes
0answers
26 views

Is Bernoulli's equation the correct explanation of a curved soccer ball? [duplicate]

I saw a lot of materials supposing that the Bernoulli's equation explains the curvature of a soccer ball: since the ball is spinning, two sides of the ball would experience different velocities, and ...
3
votes
1answer
51 views

Why does gravitational pull increase when black holes spin?

I was reading "the science behind interstellar", and found that Kip Thorne purposefully used a SMBH in his simulation which had its maximum attainable spin around its own axis. He argued that this was ...
1
vote
1answer
28 views

How are shadows and projector related?

While computing the conformal partial waves, it seems to me that $$\int d^dx |O\rangle\langle\tilde O| = \mathcal{N}^{-1}\sum_{n}|P^n O\rangle\langle P^n O|$$ where $\tilde O$ is the shadow dual of $...
1
vote
0answers
23 views

How to introduce dimensionality in a dimensionless framework?

This question is an extension of this one. I have been told that to introduce dimensionality in a dimensionless quantity I need to multiply with suitable parameters. For instance, for velocity I have ...
1
vote
0answers
34 views

A body moving along a circular path covers a distance of 3 m in 1 s uniformly [on hold]

A body moving along a circular path covers a distance of 3 m in 1 s uniformly, such that the body returns to its starting point. (i) Is the body moving with uniform speed? Explain. (ii) Is the body ...

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