All Questions

0
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0answers
3 views

deSitter spacetime metric and curvature

I have to compute the metric of an hyperboloid given by $-(X^0)^2+(X^1)^2+(X^2)^2+(X^3)^2=H^{-2}$ in 5D Minkowski spacetime using the following coordinates: $$X^0=H^{-1}sinh(Ht)\sqrt{1-H^2r^2}$$ $$X^i=...
0
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0answers
9 views

Is TT Brown's “Electrogravitics” a real thing?

Is there any actual science behind Electrogravitics and TT Brown's work? If so why haven't electrogravitics gone mainstream, taught in schools/colleges, used in developing real world propulsion ...
0
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0answers
8 views

What are good, reliable databases of atomic spectra?

I am looking for a database of atomic spectra, which contains atomic levels and their energies, electronic configurations, angular-momentum characteristics and lifetimes, and atomic transitions and ...
0
votes
1answer
13 views

“Regularization” of the stationnary solution for diffusion in spherical coordinates

In spherical coordinates $(r,\theta,\phi)$, the stationnary diffusion equation is a Laplace equation $\Delta f =0$. The solution in a radial symmetry : $f=f_{\infty}-r_0/r$ where $f_{\infty}$ and $r_0$...
0
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0answers
15 views

What is prime focus of a telescope

Telescope here refers to a system of two convex lenses. In one of the problems I wanted to solve, it is given that "a Barlow lens of focal length $f_{b}$ is placed at a distance $D < f_{b}$, from ...
0
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0answers
13 views

Approximage grid-sampled field as graph with nodes and edges

The following quiver plot shows principal direction and magnitude of a vector field in every point of a 2d grid. I'd like to condense the representation to nodes and graph edges -- unoriented edges ...
0
votes
0answers
17 views

How to calculate air density on Mars based on specicif pressure and Temperature?

I am trying to solve a Physics question which includes air density of Mars and with my calculation, I'm finding value around 0.01045: ρ_(mars,air)= P/RT= 600/((287.05).(200))=0.01045. But my ...
1
vote
0answers
14 views

Why is it that a stationary bike will fall but a moving one won't? [duplicate]

No matter how much I think about this I can't come up with a reason to me there is no difference In the forces acting against the tilting of the bike in both the cases as mothion is in the ...
0
votes
1answer
11 views

Problem in counting bonding pairs (elementary mean-field theory on the Ising Model)

When the Ising model Hamiltonian $$H=-J\sum _{<ij>} \sigma _i\sigma _j-H\sum _i \sigma _i$$ is assumed ($\sum _{<ij>}$ is the summation over all the bonds or adjacent pairs of sites, $\...
2
votes
0answers
14 views

Stability criterion for leapfrog in relativistic physics

I am doing a 2D MD simulations of charge carriers in graphene using the Leapfrog algorithm. I am trying to prove that, in some specific cases (when distance between particles is small), the method is ...
2
votes
0answers
15 views

Adding helicities

The background: I am looking at Compton scattering in its most general form with $p+\gamma^*\rightarrow p'+\gamma'^*$ in the Breit-frame (which implies that in my case $\vec{p} = -\vec{p}'$). The ...
0
votes
1answer
19 views

Ampère's circuital law in case of uniform current density in infinite space

Let's have an ideal conductor with current density $\mathbf{J}$. The ideal conductor takes up the entire space, effectively resulting in the entire space $\mathbb{R}^3$ being permeated with $\mathbf J$...
0
votes
1answer
18 views

Torque on dipole in a non-uniform electric field [duplicate]

What happens when an electric dipole is kept in a nonuniform electric field?
-2
votes
0answers
21 views

Polymer statistics

I have polymer statistics homework that i need help on: 1) Determine the force-extension behavior of the freely jointed chain (FJC) and the worm-like chain (WLC) models of polymers in the limit of ...
3
votes
1answer
96 views

Prove that if the expectation value of an operator in any state is 1, the operator is Identity

I want to prove that if $ \langle \psi | A | \psi \rangle = 1$ for all $ \psi ,$ then $A=I .$ Let's write $A$ and $\psi$ in the same basis. $$ \begin{alignat}{7} \left\langle \psi \middle| A \...
1
vote
0answers
26 views

Is the identity operator correspond to the observable which states the existence of system?

As it is claimed in this question, the identity operator is an hermitian operator, but not an observable. However, if I were to build a device, which only measures the existence of an electron in a ...
0
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0answers
13 views

Application of Piezoelectric coefficients

Which piezoelectric coefficients are suitable for which application? For example, we know that high piezoelectric charge constant are used in generators and actuators.
-2
votes
1answer
35 views

What holds together an electron when it leaves valence?

Why doesn't it release all the photons in one shot? I am referring to both in the cathode ray tube and also in the vacuum of space.
-3
votes
0answers
24 views

Sig Figs in Coulomb's Law

Because Coulomb's constant only has 1 sig fig, should all of my answers have 1 sig fig when doing a problem with Coulomb's Law?
0
votes
1answer
20 views

Question about solution to Morin Leaky Bucket problem

In Morin’s Mechanics book, a problem called leaky bucket goes: 5.17. Leaky bucket ** At $t = 0$, a massless bucket contains a mass $M$ of sand. It is connected to a wall by a massless spring with ...
2
votes
2answers
45 views

Would Newton law of gravity be the same between two neutrons at smaller distance?

Imagine 2 neutrons placed at some distance apart, they should only gravitationally attract each other according to Newton law of gravity. Theoretically the law should work at smaller distance until ...
1
vote
0answers
19 views

Magnetic flux changed by gauge transformation

This occurred to me when I was reviewing the Laughlin argument. Suppose a gauge transformation $A\rightarrow A+\nabla{\theta}$, where $\theta$ is the angle defined in a closed loop. When integrating ...
0
votes
1answer
28 views

Is there a way to make an “unseeable monitor” without modifying a computer's hardware?

What happens if you remove the polarization filter from a computer monitor? shows how to make an "unseeable" monitor from a LCD monitor, i.e. one that requires special glasses to view. I was wondering ...
-2
votes
0answers
24 views

I was wondering how to calculate the energy of amplitude for electromagnetic waves [on hold]

in science class, we have to do slides on the different aspects of waves. I was wondering if anyone could explain to me how to find the energy of amplitude
0
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1answer
24 views

Simple recoil calcuation: Difference in answer from Momentum vs Energy approach

I think I am completely misunderstanding a concept here. Depending on my approach, I get two different answers, which I shouldnt (as I understand)/ The Setup: A ...
-1
votes
0answers
20 views

Rotational motion of a spool [on hold]

A large spool of rope rolls on the ground with the end of the rope lying on the top edge of the spool. A person grabs the end of the rope and walks a distance, holding onto it, Fig. 8–64. The spool ...
-1
votes
0answers
33 views

Sound problems on frequency

Does frequency depend on the number of wavelength the source makes per second? Is it wavelengths? And what is the definition of amplitude?
0
votes
0answers
22 views

Moment of Inertia of a cone rotating from its peak

How would you prove the moment of inertia of a cone rotating around from its peak about the y-axis? I've added a roughly drawn picture for better understanding.
2
votes
1answer
26 views

When the barometer drops, my well level seems to rise - how?

I have a deep water well, with a length of 1/4" drip tubing, open at the bottom, taped to the pump 180' down. The other end of the tubing is connected to a gauge pressure sensor in the cabinet of my ...
0
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0answers
17 views

Phase difference of waves [duplicate]

Why do light and sound waves under change in phase on reflection and is the change in phase for displacement and pressure wave the same in case of sound waves??
0
votes
1answer
68 views

How much distance is there between electrons in an electron shell?

I imagine they would need keep a certain distance away from each other.
-7
votes
1answer
45 views

Is there a unified field?

Does the same force that holds the electron in orbit around the proton hold the Earth in orbit around the sun.
0
votes
0answers
12 views

How to deal with no-slip non-holonomic constraints in Lagrangian?

I'm solving a dynamical system of a ball of mass $m$ and radius $R$ rolling on a rotating platform ("turntable") for which I found the Lagrangian to be: $$L=\frac{1}{2} m (\dot{x} - \Omega y)^2 + \...
0
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0answers
24 views

I need help with a QM calculation about two entangled particles where ths spin is measured in different directions

I am trying to understand a calculation which has to do with Bell's Inequality. They start with an entangled state of an elecron and a positron which are measured along an axis a with + meaning up ...
2
votes
0answers
20 views

What happens to the $3d$ and $4s$ levels during the ionisation of a transition metal?

I'm just wondering about the transition state of a transitional metal before (ex: [Ar] 3d3 4s2) and after ionisation (which means [Ar] 3d3 4s1) because before ionisation the 4s level is closer to the ...
1
vote
1answer
27 views

Index position when varying an action with respect to the metric

I'm confused about where we should put tensor indices when we vary an action wrt the metric. For example, if I have in the Lagrangian a term such as $$ A_{\mu\nu}B^{\mu\nu}, $$ do I necessarily have ...
0
votes
1answer
39 views

Confused about Navier-Stokes equation

Just look at the L.H.S of the compressible navier-stokes equation from wiki $$\rho(\partial_t \vec{u}+\vec{u}\cdot\nabla\vec{u})=...$$ How can I add a vector $\partial_t \vec{u}$ and a scalar $\vec{...
0
votes
0answers
27 views

Relationship between physical and information entropy

This question is inspired by the following example given in Barnett's book on quantum information: (PDF here, starting at the bottom of page 5) I am not a physicist, but I'll accept that the ...
0
votes
0answers
34 views

Average number of particles in quantum well

An ideal gas of non-relativistic particles is in a box with perodic boundary conditions. I've shown that its chemical potential is given by: $$\mu=-kT\ln \left( \left( \frac{2\pi m}{h^2} \right)^{3/...
-2
votes
0answers
34 views

Big Bang, Entropy, Electromagnetic Radiation, Energy/Mass Equivalence, Gravity, General Relativity

If the photon in electromagnetic radiation does not have mass then does this mean that electromagnetic radiation is not subject to gravitational forces. Therefore it would continue at the speed of ...
-2
votes
0answers
23 views

Relativity- In a given Scenario, is FTL communication possible?

Take a black hole singularity of sufficient size that a planet could be placed in a stable orbit with a high amount of time dilation observed from the outside. Let’s assume it’s a pretty big black ...
0
votes
0answers
26 views

Worked examples of Lie derivative [migrated]

I'm trying to find the Lie derivative of a 2 form $\sin(\theta)d\theta d\phi$ with respect to a vector field given in a differential basis and I think the way to go here is to use Cartan's formula but ...
3
votes
4answers
347 views

Falling electric dipole contradicts equivalence principle?

Consider an electric dipole consisting of charges $q$ and $-q$, both of mass $m$, separated by a distance $d$. If the dipole is given an acceleration $a$ perpendicular to its moment the total ...
-1
votes
0answers
65 views

Is string theory inconsistent with the Standard Model of Elementary Particles?

According to (super)string theory, each fundamental particle represents a different vibrational mode of a relativistic string and each type of vibration pattern represents a different particle. But ...
0
votes
0answers
20 views

How do all chemical reactions result in a product whose potential is less than the reactants if all reactions are not exothermic?

We are told by our chemistry teacher that all chemical reactions take place as reactants (that have bigger potential) change into products (that have smaller potential) hence instable substances ...
-1
votes
0answers
31 views

Static electric field

What mean: "An electric field (which is static) is not a source of energy (which comes from the electron), it is a 'store' of potential energy."
0
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0answers
34 views

There are a component proportional to speed in gravitional force?

Reading some introductory texts to general theory of relativity (GR), I understand that the gravitational force between two objects has, in addition to the component in the direction of the vector ...
0
votes
0answers
14 views

Discharging a photoconductor from the substrate side

Is it possible to discharge for example an OPC drum without exposing the surface? Since they are usually build on aluminum tubes (and belt type OPCs on metallized PET or other polymer) could one drop ...
2
votes
0answers
30 views

Are there supersymmetry algebras with higher spinor representations?

The super-Poincare algebra contains supersymmetry generators $Q^I$ which satisfy fermionic anticommutation relations. By the higher-dimensional analogue of the spin-statistics theorem, they must ...
6
votes
0answers
58 views

What is the spin-statistics theorem in higher dimensions?

In $d = 3+1$ dimensions, the spin-statistics theorem states that fermionic particles have half-integer spin and bosonic particles have integer spin, in a well-behaved relativistic quantum field theory....

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