All Questions

1
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0answers
6 views

Can a spinning ball bounce off the floor without slipping?

Suppose a ball is dropped vertically downward, but it also given some spin along a horizontal axis. Then when the ball bounces, it will presumably pick up some horizontal velocity. Is it possible for ...
1
vote
0answers
12 views

Does energy conservation apply to Casmir effect?

If you cancel out some quantum field modes using two 'casmir' plates you decrease the average energy density in the region and gain potential energy in Casmir force approximately proportional to the ...
0
votes
1answer
13 views

tensor products of exponential annihilation operators

I'm hoping to use this stackexchange to solve a gate decomposition problem, but I am stumped, so hoping for help. These definitions come from the Xanadu Strawberry Fields whitepaper on Table VI and ...
0
votes
0answers
6 views

Supercurrent of the $bc-\beta\gamma$ SCFT

In Polchinksi's Sec. 10.1, the $bc-\beta\gamma$ SCFT is introduced with action $$S_{BC} = \frac{1}{2\pi} \int d^2z (b \bar \partial c + \beta \bar \partial \gamma)$$ and supercurrent $$T_F = -\...
0
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0answers
8 views

What happens when electron keeps hitting on a metal plate

In SEM, in order to 'focus' the electron beam, an aperture is used (which usually is metal); what happens to the metal after so many electron hits the metal constantly? since metals are usually are ...
1
vote
2answers
14 views

Suppose A and B represents two vectors travelling(insame order), the angle between them being 60 degrees, then why is the resultant wrong?

Let's say there are three points A,B and C: A represents the displacement between points A and B (4 cm to the east) and B represents the displacement between the points B and C (3cm to the northwest)....
0
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0answers
5 views

Canceled term in Brownian Motion's mean squared distance derivation starting from Langevin's equation

In Feynmann's Lectures on Physics, chapter 41, part4, In the derivation of the Browian expression for the mean square distance Feynmann's starts off with the lengevin Equation $ m\frac{d^2 x}{dt^2} ...
0
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0answers
9 views

Heat Capacity for Conduction Electrons in a Metal

This is a problem from one of the past papers that I am doing in preparation a resit exam that is coming up soon: Consider the derivation of the heat capacity for conduction electrons in a metal. a) ...
-2
votes
0answers
18 views

Deriving $C=\varepsilon_{0}\varepsilon_r \frac{A}{d}$

I have been looking for ages but cannot find derivations of the capacitance formula $$C=\varepsilon_{0}\varepsilon_r \frac{A}{d}$$ on the Internet. I would really appreciate it if someone could point ...
0
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0answers
19 views

Dependence of radial probability function on quantum numbers

I was reading the book "Quantum Physics" from Eisberg & Resnick about the expected value of the electron radial coordinate, which it defines as \begin{align} \overline{r_{nl}} = \int_{0}^{\infty}...
0
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0answers
20 views

Einstein Solid Question

[From The Oxford Solid State Basics by Steven H Simon] (2.1) Einstein Solid a) Classical Einstein ( or "Boltzmann") Solid: Consider a three-dimensional simple harmonic oscillator with mass m and ...
0
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0answers
13 views

What do fringe patterns have to do with VLBI?

I think I have fundamental confusions with how VLBI works. I don't know why: Resolution increases when incident rays meeting to a focal point from a farther separation along an axis perpendicular to ...
0
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0answers
31 views

Relativity and differential equation

I have a question regarding Misner, Charles W.; Thorne, Kip S.; Wheeler, John Archibald (1973), Gravitation ISBN 978-0-7167-0344-0. It is a book about Einstein's theory of gravitation. In page 166 of ...
2
votes
0answers
47 views

How can I explain what a kilogram is using Planck's constant?

I want to understand what 1 kg represents. For example: I know that 1 second is equal to $9\ 192\ 631\ 770$ transitions from the microwave radiation that a cesium-133 atom (at $0$K) emits, if it's ...
0
votes
0answers
16 views

Electrical Field and Potential of a Spherical Capacitor

Problem: Consider two concentric, infinite thin, homogeneous charged spherical shells centered on the origin with $r_1 < r_2$ and charge $q>0$ respectively $-q$. Calculate the electrical field ...
0
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0answers
9 views

Anomalous dimension of double-trace operators

Is it true that if a single-trace operator, say, $O$ acquires an anomalous dimension $\gamma_o$, then the anomalous dimension of the double-trace operator $O^2$ is $2\gamma_o$? If no, can anyone ...
2
votes
1answer
24 views

Are the field equations describing quantum fields in a curved space time generally co-variant in the same sense as classical field equations?

I have seen in many references that the field equations for a quantum field in curved space time is mentioned to be 'manifestly co-variant'. The procedure that has been followed to arrive at these ...
0
votes
1answer
29 views

In zero gravity!

If a spacecraft moving in a stable speed or acceleration and suddenly stopped did a astronaut will continue moving forward ( such as a man in a train) ?
0
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0answers
10 views

When is tension inversely proportional to acceleration?

So I have questions where 2 pulleys are present, and when one of them is fixed to a rigid support on one end, it is said that tension is inversely proportional to acceleration. On the other hand, ...
0
votes
1answer
13 views

Does the amplitude of light increase the more it is squeezed? (Quantum Optics)

If I have a 2 mode squeezed state of light, emitted from some nonlinear parametric process, then the more it is squeezed, the larger the variance of one quadratures $X$, while the variance of the ...
0
votes
0answers
38 views

Is the $U(1)$ in the standard model identified with quantum-mechanical phase?

I think there's a tension between two claims I've read: The standard model is Yang-Mills theory with gauge group $SU(3) \times SU(2) \times U(1)$. Here the $U(1)$ factor is data on the same level as ...
0
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0answers
15 views

Exact difference between '''Fermi normal coordinates''' and ''Riemann normal coordinates'''? [duplicate]

I want to know the exact difference between '''Fermi normal coordinates''' and ''Riemann normal coordinates'''? Here is a same question, but it's hard for me to understand. Difference between Fermi ...
0
votes
2answers
46 views

GR visualization

I'm watching some GR lectures by Schuller (more or less rushing through them so bear with my ignorance here please) in Lecture 10: Metric Manifolds. He's talking about geodesics in a manifold with a ...
2
votes
0answers
17 views

An equivalent computation of a Feynman diagram

A typical second-order diagram for the self-energy gives integrals such as: $$\int \int d \omega^\prime \omega^{\prime \prime} g(\omega-\omega^{\prime})g(\omega^{\prime \prime})g(\omega^{\prime}+\...
-2
votes
0answers
23 views

Random distribution and probability [on hold]

Consider a rectangle of specified length and width, we randomly distribute $n$ points on it. What's the probability of finding no point in an interval of length $x$ and let the width be fixed as '$w$...
0
votes
1answer
27 views

Equation of State

Given is next relation: $S = a [NVE]^{1/3}$ and $a$ is a constant. I have to find the Equation of state. So I started by using some thermodynamic identities: $\frac{\delta S}{\delta E} = \frac{1}{T}$ ...
-1
votes
0answers
24 views

How can I verify/validate a private research? [on hold]

I'm an amateur researcher, who's interested in plasma physics and space weather. I'm trying to find a professional physicist, who would be kind enough, to give me a professional opinion about a model ...
1
vote
2answers
28 views

How long does it take to cool down a drink with ice?

If I have a bottle or container with X fluid ounces of water at temperature Y (say, fridge temperature or room temperature), and I put ice or ice sticks (composed of water) in it that make up Z fluid ...
0
votes
0answers
13 views

What shape of gravity and EM fields would a hollow sphere produce, with what resulting effects upon said structure?

The Earth generates a gravity field based on local mass, but which mostly appears to act as a point source, though local fluctuations in the crust density and mass affect the gravity in a given region ...
0
votes
0answers
13 views

What “manifold in band parameters ” means?

I was reading an article https://arxiv.org/abs/0907.0500 in which they write about manifold in band parameter ,like in first line in my picture , and then they call it band parameter . can some ...
1
vote
1answer
28 views

Why is an action built from superfields guaranteed to be supersymmetric?

Given a superfield (in 0+1 spacetime + 2 superspace coordinates) $$X(t,\theta_1,\theta_2) = x(t) + \theta_i \psi_i(t) + \theta_1 \theta_2 F_{12}(t)\tag{1}$$ and given the standard supercharges ...
0
votes
0answers
25 views

Understanding Bell's Inequality?

I'm struggling to understand Mermin's article "Is the moon there when nobody looks?". Is it possible to reduce the number of measurement modes from 3 to 2? For example, with an experimental setup with ...
-1
votes
2answers
22 views

Stuck on determining velocity?

The main question was: A car travelled 50 metres in 5 seconds with constant acceleration and initial velocity being zero. What will be the velocity after 15 seconds? I tried to solve by this way, $...
-1
votes
0answers
15 views

Dimension of distance travelled in $n$th second and velocity [duplicate]

Why is the dimensional formula of distance travelled by a particle in nth second of time same as that of velocity? It's really confusing for me to understand this, after all it's distance but still ...
0
votes
0answers
17 views

Where does differntial equation of covariance matrix come from?

Does anyone know where the differential equation of covariance matrix comes from? $$\frac{dC(t)}{dt}=AC(t)+C(t)A^T+D$$ where C is the covariance matrix, ...
0
votes
0answers
14 views

Turing Pattern wavenumber

I don't know the relation between the experimental wavenumber that I can obtain from the Fourier spectrum of the simulated pattern and the theoretical critical wavenumber that gives me the linear ...
1
vote
1answer
27 views

Why is it so that some of the paper pieces get stuck to it while others drop instantly when they stick?

When we rub a comb on our head and held it near pieces of paper then they get attracted because of induced opposite charge.
0
votes
0answers
19 views

Does water have a minimal thickness because of van der waals force?

I have read this question: The thickness of a puddled sheet of water https://en.wikipedia.org/wiki/Surface_tension#Puddles_on_a_surface The liquid mass flattens out because that brings as ...
0
votes
1answer
68 views

Explain the last paragraph of this text

First, look at the first paragraph of the second page. It says: The things that you can see at some time are the inside of the light-cone at o. I don't get it. Suppose an event happened outside ...
0
votes
1answer
18 views

Regd. derivation of some equations in “Bertrand Spacetimes” by Pelick

We are going through "Bertrand Spacetimes" by Dr Perlick, in which he first gave the idea of a new class of spacetimes named as Bertrand spacetimes after the well-known Bertrand's Theorem in Classical ...
1
vote
2answers
38 views

Black spot when switching intensity of light

Whenever I look at a bright light source and then turn my eyes away I see a large black dot blocking a part of my vision. Does this has something to do with Physics as it involves light or it is ...
0
votes
2answers
40 views

Change in kinetic energy of pendulum

"An object of mass m is tied to a string of length L and a variable horizontal force is applied on it which starts from rest and pulled slowly until the string makes an angle $\theta$ with the ...
0
votes
0answers
33 views

Mathematical Model for a Pendulum in an Electric Field

I am studying Higher Level Physics and for my Physics IA I am doing an experiment determining the effect of the voltage between two parallel plates on the on the frequency of a pendulum in between the ...
0
votes
0answers
9 views

Quantum Fisher information for Gaussian states without eigenproblem?

Given a Gaussian-preserving interaction (including a unitary operation and losses) for a Gaussian input, I want to know if there is an "easy" way to compute the Quantum Fisher information without ...
0
votes
0answers
30 views

Time needed for an electron to move 15cm

An electron has a speed of $2\cdot10^4 m/s$, then it goes inside an electric field $\vec{E}=900 N/C$ with direction to positive Y-axis. Without considering the weight force of the electron, the time ...
1
vote
0answers
40 views

Is there any reason that Landau and Lifshitz don't discuss Noether's theorem in their mechanics book? [on hold]

I'm currently working my way through the Course volume one. Unless I've completely missed it, the authors omit any discussion of Noether's theorem, instead deriving various conservation laws on a case ...
1
vote
1answer
33 views

Intuition on the overall entropy increase caused by heat transfer

Let's say that Hotter Gas A loses heat to Colder Gas B. Heat is transferred from A to B in such a way that the overall entropy increases. This can be proven with equations, but what is the intuition ...
0
votes
0answers
14 views

Connecting two reservoirs

When we connect two reservoirs kept at $\mu_{1}$ and $\mu_{2}$ respectively the potential difference is given by $(-e) V=\left(\mu_{1}-\mu_{2}\right)$. While if the conduction of electrons occurs ...
0
votes
0answers
12 views

An elastic collision of a rigid body with a wall [on hold]

I thought about a problem that I could'nt solve myself. let's say we have a cylinder with mass M and radius R, rolling on the floor without slipping. The velociy of the center of mass is V1 and the ...
0
votes
0answers
19 views

Why RMS for average voltage in AC current? [duplicate]

We write rms formula as $$v_{rms}=\sqrt\frac{\int_a^b[f(x)]^2dx}{|b-a|}$$ I know if we take arithmetic mean average voltage will be 0. So we want all voltage values to be positive. Why don't we do ...

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