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a single electron and a detector for magnetic fields. If the electron is moving at a constant velocity, will the detector ever register a magnetic field?
|
In the study of thermal radiation, emission is usually described in terms of solid angles.
My question is: why is $dA_{jp} = cos(\theta_j ) dA_j$ in the below figure? How can I understand this geometrically? I tried deriving this relation by starting with the fact that $dA_{jp} = rd\theta * rsin(\theta)*d\phi$ then got... |
I want to start learning physics, could you recommend books and/or other resources to get me started in this field?
I would also like you to tell me what things I should keep in mind before I start learning physics
|
In §29 of L&L mechanics, the authors discuss an approach to estimate the resonance amplitude of the equation
$\ddot{x}+2\lambda\dot{x}+\omega_0^2x = \frac{f}{m}\cos(\gamma t)-\alpha x^2-\beta x^3$
In particular, they use the formula for the amplitude b of the driven oscillation derived from the problem without nonline... |
The question, which weighs more, one pound of feathers or one pound of black hole, comes to mind. Each would react wildly different reentering Earth's atmosphere. In order to narrow the question: Is there a simple object/devise with the right parameters with the right entry angle that can enter the atmosphere to decele... |
I’m rephrasing a suggestion as a question because there was an aspect to it where I wanted to know more as well.
I have studied both general relativity and particle physics, though in both cases my experience with theory ended around the time of my general exam in graduate school (because I switched fields, did data an... |
I'm asking about the case where an infalling object travels a path right through a rotating black hole, intact.
I want to provide a simple parallel for the purposes of question clarity:
A horse can take me from my house to a paddock, from Point a to Point b. Something then spooks the horse, a descending hot air balloon... |
I'm following K. Huang's QFT: From Operators to Path Integrals book. In the second chapter, he introduces the Klein-Gordon equation (KGE), and its scalar field $\phi(x)$, which satisfies this equation. He then gives an Ansatz for this scalar field:
$$\phi(x) = \frac{1}{\sqrt{\Omega}}\sum_{k}q_{k}(t) \, \text{e}^{i\math... |
I'm a grad student studying the fractional quantum Hall effect. To get started, I read chapter 9.5.1 of A. Altland and B. Simons' Condensed Matter Field Theory.
They use the composite fermion (CF) approach, where they attach two flux quanta to each microscopic fermion via a gauge transformation.
Their starting point is... |
We can compute the "proper circumference" of the Schwarzschild event horizon integrating its line element along its perimeter at a fixed $t$. This would be the minimum length of a rope that goes arround the black hole measured by the static observers that mantain it just above the horizon. (I am using $\tau=2\pi$).
$$C... |
In general textbook, when we want to calculate the dimension of moduli space of string compactification, i.e. calculate the number of massless modes after dimension reduction, we use the following equation
$$\Delta_{10 d}=\left(d d^{\dagger}+d^{\dagger} d\right) \mathbf{X}_6+\Delta_{4 d}$$
This means that the kinetic t... |
In the infinite square well, there is zero probability of finding a particle at nodes. What is the meaning of this result? Does the particle teleport in the regions between the nodes?
Or is it that this is a meaningless question in standard Copenhagen interpretation?
Based on the comments on this question, I believe th... |
The following integral of lookback time gives the age of the Universe with matter (dark + baryonic) density $\Omega_m \approx 0.3154$ and $\Omega_{\Lambda} \approx 1-\Omega_m$, ignoring radiation density and curvature:
$$t_L = (1/H_0) \int_0^{\infty} \frac{dz'}{(1+z')\sqrt{\Omega_m(1+z)^3 + \Omega_{\Lambda}}}$$
where $... |
I have seen a few Sagnac fiber optic interferometers however, those that I've seen don't produce multiple fringes but rather just one luminant dot with varying intensity. Even if a beam expander is installed still there are no fringes but only one light dot. What is the reason for this behavior. Here is an example of a... |
Hiii, im trying to derive a result of a paper i having problem.
I have a flux of particles described by the equation: $Φ=Φ_0cos²(θ)$, where $\theta$ represents the zenith angle. In addition, I have a tank with a radius RR, and I can assume that the lid area is much larger than the lateral area of the tank.
My goal is ... |
In my physics class we are learning about how objects with greater rotational inertia result in less translational velocity when "rolling without slipping" down an incline. When explained, it is taught that more rotational inertia will result in more rotational kinetic energy being converted from gravitational potentia... |
For now, let $\hat{\phi}(x)$ be a quantization of a classical, real scalar field $\phi(x)$.
My understanding is that, for fixed $x$, there are three ways to regard the operator $\hat{\phi}(x)$:
The value of the classical field $\phi$ at $x$ is an observable, so $\hat{\phi}(x)$ is simply the operator corresponding to t... |
The starting points of this theorical exploration are the following.
I do believe we exist in a universe where 10 (or 11) dimensions do exist, but the ones beyond 3 spatial + 1 time are compactified.
I am not interested in answers refuting this, not as a sign of arrogance but just because they would miss the point of m... |
Consider the bottom of a wing.
Air below the wing is deflected downwards by the wing. Hence by Newton's 3rd Law the wind must exert an equal and opposite force on the wing. Hence lift, and this makes logical sense.
What becomes confusing, is explaining how lift is created at the top of the wing. Air once again moves do... |
In many papers and books, including paper written by P.Gondolo & G.Gelmini in 1991, COSMIC ABUNDANCES OF STABLE PARTICLES: IMPROVED ANALYSIS, it is well known that for non relativistic gas, you can write down annihilation cross section times relative velocity $\sigma v$ by expanding this in powers of $v^2$ when you can... |
I am currently working on simulating the scattering of light from nanoparticles. Are there any resources like books/ handouts/ videos that explain Mie Theory in depth?
|
When an elevator suddenly starts decelerating downwards after the cable snaps, why does the person inside the elevator float upwards? In such a scenario why aren't the elevator floor and the person always in contact because the only force that is acting on both objects is gravity so should they not be accelerating at t... |
I'm concerned about the following scenario of polarization in a perfect dielectric:
When a material is exposed to an electric field it develops polarization proportional to the electric field.
From here, books say that you can integrate the small polarization dipole moments in the material to find their combined effect... |
I have been searching online for these. I found somewhere that momentum components calculated using momentum operators are covariant because gradient transforms in covariant fashion. But I am having trouble finding the contravariant form. From my teacher’s slide, I am giving the two forms provided (I don’t understand t... |
In Thermodynamics (1st ed.) by James Luscombe (2018, p. 12), the zeroth law is used to show the existence of empirical temperature (of fluids in thermal equilibrium) as a function of pressure and volume. This notion of temperature is a logical consequence of the zeroth law. Am I right?
However, in An Introduction to Th... |
In statistical mechanics class , it is assumed $\Omega(E) \propto E^N$ where $\Omega(E)$ is the no of microstates corresponding to energy E in a system where no of particles is constant and total energy of reservoir and system is constant. The system is in contact with a reservoir and N is the total no of particles in ... |
I know the KE equation for combined translational and rotational motion, which is $K=Mv^2/2+I\omega^2/2$, and here $v$ is the velocity of COM and $I$ is the moment of inertia about the COM. But what if the body rotates about a point $\mathcal{P}$ other than the COM? Can I use the the velocity of $\mathcal{P}$ and momen... |
I wanted a way to "derive" Gell-Mann matrices for $\mathfrak{su}(3)$ and generalise this to other semi-simple algebras $\mathfrak{g}$. The way I wanted to approach this is start from the Dynkin diagram/Cartan matrix and find out the roots of the algebra and weights of the fundamental representation. This gives me in tu... |
I hope this question won't be closed.
There is a machine called oracle which appears in a lot of algorithms of quantum computing, such as Deutsch's algorithm and QFT period-finding.
This oracle machine really makes me confused.
I've read something about computing theory, and in that, it mentions the oracle as a machine... |
According to the standard quantum mechanics, quantum states are one-dimensional subspaces of a separable Hilbert space. In practice, this Hilbert space is $L^2(M)$ where $M$ is the classical configuration space of the system. From this follows that for any state function $\psi_1 \in L^2(M)$ and for any $z\in\mathbb C\s... |
I was reading the following paper by Landau and Lifshitz on ferromagnetism:
https://www.sciencedirect.com/science/article/abs/pii/B9780080363646500089
In the paper, the following expression is used for the density of the energy of the system (inhomogeneity+anisotropy):
$$ 1/2 \alpha s'^2+1/2 \beta (s_x^2+s_y^2) $$
Wher... |
We know angular momentum is defined as $mvr$. In the context of Lagrangians and Noether's theorem, this definition pops up as the conserved quantity due to rotational symmetry of the system. Is there anyway to justify this definition without the use of Lagrangians and Noether's theorem? As in if we try to generalise li... |
How to derive the first-order perturbed Klein-Gordon equation:
$$ \square \phi=\left[\frac{1}{\sqrt{-g}}
\partial_{\mu}\left(\sqrt{-g}g^{\mu\nu} \partial_{\nu} \right) \right]\phi=0$$
For a first-order perturbed metric:
$$ g_{00} = -a^2 ( 1+ 2 \Phi), ~~~ g_{0i} = 0 , ~~~~ g_{ij} = a^2 (1-2 \Psi).
$$
Here is my trial:
... |
In this question the people who answered helped me validate my understanding of the $\vec\omega$ vector, the angular velocity of a particle or a rigid object.
I would now like to add the angular acceleration $\vec\alpha$ into the mix, and validate my understanding.
This question assumes that a rigid body, or a particle... |
Is this condition correct, "if liquid and gas heated from top, then it will be possible for 'conduction' to occur" ?
One reason i can think is :
when liquid or gas is heated from sideways or below,the heat transfer will take place through 'convection' and not through 'conduction'.
And only when we heat from top, there... |
I am new to looking at phonons, especially in relation to their use in coupling to electrons.
Phonons can be defined as the treatment of vibrations in a crystal lattice. There can be different types/modes of phonons such as acoustic (longitudinal and transverse), long-wavelength, optical phonons and im sure there are m... |
Let's take a process with constant pressure in ideal gas for example. in reversible process
$dS=\int_{1}^{2}\frac{\delta Q_{rev}}{T}=\int_{1}^{2}\frac{C_pdT}{T}$
Assuming constant specific heat capacity, the result is state function, so is the entropy. Then we learned that $dS=\int_{1}^{2}\frac{C_pdT}{T}$ is true for ... |
When you rub a glass rod against silk cloth, the glass rod becomes positively charged and the cloth becomes negatively charged. So they now can attract each other.
However, after this 'attraction' takes place, the effect is lost after the objects neutralize or nullify each others' charges.
What happens when a comb rubb... |
I am currently writing an algorithm to generate bidisperse random close packed configurations of disks with the aim of calculating the packing fraction with varying disk concentration $p$ and disk ratio $D$.
The broad outline of the algorithm is as follows:
Begin with a deterministically disordered nucleus of 6 disks
... |
The moon causes a tidal bulge because there is a differential in the gravitational field on the near vs far side of the Earth and the ocean is fluid and can distort to seek the new equilibrium state as the moon moves.
But this depends on the waters on all sides of the Earth being connected, right? As the tidal bulge ex... |
To be specific,I've been considering a simple case where a fluid is under uniform gravity.
For hydrostatic equilibrium,$\nabla P=-\rho g$and the distribution will be like $\rho(z)=\rho_0 exp[-mgz/kT]$.
What confuses me is,according to Fick's law,$\frac{\partial \rho}{\partial t}=D\nabla^2 \rho$,and the hydrostatic dist... |
This is a question on work-energy theorem in rotational motion with its answer for the first part of the question. Here, I have a doubt about why is the book taking the translational work done by the gravity and not the rotational work done by the gravity? I can not understand this question, please help
|
Is it possible to have a magnetic configuration without a north and a south pole?
My school textbook says that it is possible, as in the case of toroid and a wire carrying current. Now, the explanation given suggests that this type of case is possible if and only if a configuration has a net zero magnetic moment, as in... |
I recently tried to derive the reflection coefficient $R$. This is not a complicated task, however after making some literature research I found two derivations which arrive at seemingly different results:
The first derivation is from Griffiths ‚Introduction to Electrodynamics‘. In chapter 9.1.4 he derives the reflect... |
The wikipedia definition
Electric flux is the measure of the electric field through a given
surface,
More formally ,The electric flux $\Phi$ through a given surface $S$ is
defined to be $$ \Phi=\int_S \mathbf E\cdot\mathrm d \mathbf S. $$
Firstly ,why is there a need to define such a quantity i.e what exaclty is it m... |
I searched on the internet superficially but I couldn't find it.
Is there any reference that find the solution to Einstein's Field Equations for a rotating Cosmic String?
Personally haven't got the time to do the computation for the rotating flux tube extension of a 2d vortex solution to the Higgsed-$U(1)$ Yang Mills, ... |
How does the packing fraction of a nucleus affect the stability of the nucleus? A true and false based statement question came in a exam I gave, and it stated the statement "The stability of a nucleus is inversely proportional to its packing fraction" to be "True". Google search doesn't reveal any helpful articles, tho... |
Using the symetric gauge $\mathbf{A} = \tfrac{B}{2} (-y, x, 0)$, the stationary states wave functions of a quantum particle in a constant and homogeneous magnetic field are
$$\tag{1}
\psi_{n m}(r, \varphi) = a \sqrt{\frac{n!}{\pi (n + |m|)!}} \, u^{|m|} \, L_n^{|m|}(u^2) \, e^{- u^2/2} \, e^{i m \varphi},
$$
where $u =... |
Why is the total force taken as zero
|
We know that the magnetic field can be written in the following way:
$$\nabla_{\vec r }\times\vec B(\vec r) = \frac 1 c \nabla_{\vec r}\times\int d^3\vec r_q\ \vec j(\vec r_q)\times \frac {\vec r-\vec r_q}{|\vec r-\vec r_q|^3}$$
and, using the $BAC-CAB$ identity, the curl of this becomes:
$$= \frac 1 c \int d^3\vec r_q... |
Does stress-energy tensor of a $2\text{d}$ conformal field theory split into holomorphic and anti-holomorphic parts as follows?
In a conformal field theory, stress-energy tensor $$T_{\mu\nu} = \frac{1}{\sqrt{-g}} \frac{\delta S}{\delta g^{\mu\nu}}$$ is traceless as a consequence of the invariance of $S$ under a Weyl tr... |
A drum is rolling down a hill without slipping. We ignore air drag.
In order for the drum to not slip, there must be a (static, correct?) friction force exerted by the surface on the drum at the point of contact.
This friction force acts in the direction opposite to the velocity of the center of mass of the drum.
In an... |
If we have an object which is acted upon by a force which which produces both translational and rotational motion of body then would the total work done by the force be the sum of its translational and rotational work?
|
So suppose I have a bunch of particles interacting among themselves with a potential function that is arbitary (not defined).
The total potential energy of the system is the sum of individual interactions.
How can it be possible that as the potential enrgy of the total system increase the number of degeneracy also incr... |
Is there any natural interpretation for the following quantity?
$$\int_{\vec{r}(t)} \nabla(\vec{v} \cdot \vec{A})dt \ .$$
Where: $$\vec{v} = \frac{d \vec{r}(t)}{dt} \ ,$$ is the velocity of the path over which the integration is done; and $\vec{A}$ is some vector field (with units of momentum). I believe it can be rewr... |
Is this new image (below) of polarized light surrounding Sagittarius A, showing actual frame dragging being captured by the magnetic field? The image is from this article If not, how would a photo showing frame dragging in the magnetic field look any different?
|
Let a coherent fermionic state
$$
\left|\phi\right> := \left|0\right> + \left|1\right> \phi,\tag{0}
$$
where $\phi$ is a Grassmann number (i.e. it anticommutes with other Grassmann numbers). Now, I wish to see if it's orthogonal to another state $\left|\phi'\right>$:
$$
\left<\phi|\phi'\right> = \left[ \left<0\right| +... |
There are two objects A and B. Points P1, P2, P3 are in the same line, and P2 is exactly at the middle of P1 and P3
Suppose B is moving at constant velocity along the line P1 to P3. Thus, time taken by B to reach from P1 to P2 is same as that from P2 to P3. Let's assume this time is 1 second.
But if we observe B's vel... |
A vertical ideal spring with spring constant of 92 N/m is placed on top of a lab bench. A block of unknown mass, m, is dropped onto the spring from a height of 1.1 meters above the lab bench. Before the block hits the spring, the spring is 0.4 meters long. Once the block comes to rest after hitting the spring, the spri... |
I have problems understanding how the square of the momentum operator should look like in QFT.
Very likely, I'm making some mistakes somewhere but I'm not sure about it.
Let us consider a simplified setting of a 1-dimensional QFT.
Starting from a position representation and then writing the fields in momentum space, th... |
Regarding electromagnetism, a changing magnetic flux$(\phi_B)$ produces emf by-$$EMF= -\frac{d \phi_B}{dt}\tag1$$
This emf creates a current which again creates a magnetic field given by-(bio-savart law) $$dB= \frac{kI×dl}{r^2}\space\space\space\space\space\space (2)$$ assume appropriate constants and vectors.
But if t... |
I have following three doubts.
For a particle in a box problem, a particle is moving within a box of length a. The normalization constant is $\sqrt{\frac{2}{a}}$. My question is if we take a negative integer (i.e. value of quantum number as -1, -2, ...... etc), then it will give a different solution like $-\sqrt{\frac... |
It sometimes happens that utilities have so much energy they have to pay other utilities to take it. From https://www.latimes.com/projects/la-fi-electricity-solar/:
On 14 days during March, Arizona utilities got a gift from California:
free solar power.
Well, actually better than free. California produced so much sola... |
Lie derivatives signifies how much a vector (Tensor) changes if flown in the direction of some other vector. I am thinking the typical moving boat on a flowing river problem where the river is flowing in the X direction with constant speed and the boat is moving in the Y direction with constant speed. After some time t... |
I was reading about quantum capacitance and came across the following formula:
$$\Delta \mu = \frac{N}{\rho}$$ where N is the number of electrons moved from the metal to the low-density-of-states material, and $\rho$ is the density of states of the low-density-of-states material.
I am having a hard time understanding w... |
Please help me. This is my assignment problem.
We know the following integral for the particle in a one-dimensional box
$\int_{0}^{L/5}\psi_5^2 (x)dx=\frac{1}{5}$.
How does this value compare to that for the integral over the same range, but using $\psi_1$ instead of $\psi_5$? (Larger, smaller, or equal?). I calculated... |
Consider single hydrogen atom in the ground state. Does there exist an experimental procedure that would determine the 0th component of the current $J_\mu(x) = \bar{\psi}(x)\gamma_\mu \psi(x)$ created by the electron as a function of spacetime point?
|
Recently I’m learning about lagrangian fomulation in GR. And I’m doing some calculations for some toy models.
I precisely understand the variance of christoffel, Riemann tensors about metric, but when it comes to some arbitrary fields, I’m confusing about the manner of their transformation rules.
Suppose that we’ll con... |
In classical mechanics the concept of energy is very simple. If I have a bunch of particles $r_1$...$r_n$. Then the total energy is:
$$E=\frac{1}{2}m(\dot r_1^2+...\dot r_n^2)+U(r_1...r_n)$$
Now in thermodynamics; I read from callen's book that Energy is a function that dependa on volume ($V$); number of particles ($N$... |
I am working on deriving the intensity equations for the dynamical diffraction of neutrons following along with a paper by Hartmut Lemmel (Hartmut Lemmel. Dynamical diffraction of neutrons and transition from beam splitter to phase shifter case. Phys. Rev. B, 76:144305, Oct 2007).
The first task is to get the following... |
In "Introducion to Quantum Mechanixs", at p. 16, Griffiths writes what follows:
Now, if $\Psi$ is just assumed to be in $L^2(\mathbb{R})$, this does not imply that $|\frac{\partial\Psi}{\partial x}|$ is bounded for $x\to\infty$, so along particular sequences $x_n\to\infty$ the limit of $\Psi \frac{\partial\Psi^*}{\part... |
It's mentioned in this paper that if $\partial^i \partial^j$ applied on an equation like:
$$
x \delta_{ij} + (\nabla^2 \delta_{ij}- \partial_i \partial_j) y =0
$$
It yields a couple of equations:
$$
\nabla^2 y=0,
$$
and,
$$
x=0
$$
This means:
$ \partial^i \partial^j \delta_{ij} =1 ~~~ \star$
And
$
\partial^i \part... |
I understand that electrons can't cross an open switch, but why don't they at least move towards the open switch when a battery is connected? Doesn't the voltage cause motion towards the positive terminal?
|
In quantum field theory (specifically $\phi^4$ theory), $W$ is the sum of all connected Feynman diagrams and the effective action $\Gamma$ is the sum of all 1PI Feynman diagrams. They are related by a Legendre transform. Then $W^{(n)}$ and $\Gamma^{(n)}$ represent $n$-point connected correlation functions and $n$-point... |
Suppose a ball is connected to a spring attached to a wall, and they are in space, i.e. assume no gravity. The ball is put into a fluid with Stoke's drag and oscillates backwards and forwards relative to the wall. The ball has a mass m and displacement x = acoswt. What would the displacement x be if ma = -kx-bv where b... |
Imagine you have some optical spectra (intensity vs wavelength) you want to measure. You do so by measuring the intensity of the spectra hitting a detector after placing multiple long pass optical filters in front of the detector. Each successive long pass filter has a longer wavelength at which it allows light to be t... |
The equation you provided, $(S_{\text{Axial}} = \frac{\omega}{M_{\text{System}} \times M_{\text{External}}})$, has several implications related to angular momentum and rotational dynamics:
Angular Momentum Conservation:
The equation highlights the conservation of angular momentum in a system.
When no external torques a... |
I was thinking about transplanckian energy $E>10^{19}GeV$ magnetic monopoles in string theory and M-theory. Are they possible in Nature like the Dirac, 't Hooft Polyakov, Julia-Zee monopoles/dyons? What are the issues (if any) from theory/experiment?
The answer should contain ideally also answer to some of the followin... |
So I know that in an $RC$ circuit
$v = R\frac{dQ}{dt} + \frac{Q}{C}$
with voltagev and resistance and capacitance R and C, respectively.
$\implies$ Q = $vC(1-e^{\frac{-t}{RC}})$
Therefore the voltage across the capacitor is given by:
$$v_C =v(1-e^{\frac{-t}{RC}})$$
Since the voltage across the resistor($v_R$) = $R\frac... |
I have read this:
Because the spacetime curvature at the horizon is so great that there is no light-like world line the extends beyond the horizon.
Why does time stop in black holes?
If the curvature is extreme, that would that mean that laser beams (for the sake of argument let's assume they are visible because of ... |
I have been thinking about how to get a general solution for the continuity equation:
$$\frac{\partial \rho(\vec{r},t)}{\partial t}+\vec{\nabla}\cdot\vec{J}(\vec{r},t)=F(\vec{r},t)$$
and I figured the way to proceed is to reduce the problem to one I already know how to solve. Therefore, under the condition that the cur... |
Could somebody help me derive this equation?
$$\frac{\mathrm{d}M}{M}=-\frac{\mathrm{d}v(1-v_\mathrm{ex}\frac{v}{c^2})}{(1-\frac{v^2}{c^2})(-v_\mathrm{ex}\frac{v^2}{c^2}+(1-a)v+av_\mathrm{ex})}
$$
This is purportedly the relativistic rocket equation when accounting for annihilation to usable exhaust. To quote Wikipedia,... |
Transformers have no moving parts in direct contact with other solids, do not rely on non-reversible chemical reactions, and do not rely on nuclear reactions. So, with inert materials, the atomic bonds that make up the transformers should theoretically never change after it is manufactured.
As far as I know, commercial... |
For the the 1D atomic chain tight binding calculation, if we choose 1 atom per unit cell, the band dispersion is simply: $\epsilon-2t\cos{(ka)}$.
However, if we redefine our unit cell as 2 atoms, 3 atoms...n atoms. Why don't we end up with a $n\times n$ hamiltonian and end up with n different bands? It seems now the n... |
If you have molecules of air colliding compared to a different element, will one be more elastic?
So if 2 molecules of some other element collide, will that be more or less elastic than 2 air molecules colliding?
For example, if said molecule had a higher mass than an air molecule. Would that change anything?
|
I was thinking about the magnetic field at the center of a loop of current and tried to calculate the field using results from Ampere's law. I understand that directly using Ampere's law does not work as there is not a suitably symmetric loop to consider for a current loop; however, I am struggling to see why my approa... |
Are there a few different ways of using the term 'energy scale' that differ in their precise meanings? For instance, in the context of the chart provided, 'energy scales' denotes the magnitude of energy required for probing particles in particle accelerators to interact with specific particle types for the purpose of s... |
Balloons can be balanced to have just enough string to be suspended off the floor with the end of the string touching the floor. Another balloon could then also be stacked and top of that balloon in the same manner. What would prevent airships, other than wind where windless regions do exist on Earth, from being stacke... |
I've just started studying Lagrangian mechanics and am wrestling with the concept of "action". In the case of a simple harmonic oscillator where $x(t)$ is the position of the mass, I understand that the Lagrangian is written down as $L = T - V$ (difference between kinetic and potential energy), and that one can use the... |
I've taken a course in graduate statistical mechanics, and it seems like the concept of statistical ensemble is flexible. We talked about Micro and grand canonical, as well as one or two more. I'm curious about what kinds of existing and hypothetical ensembles exist within the physics community.
|
To calculate the Big Crunch time (time since an expanding universe starts expanding until it collapses), starting from the first Friedmann equation:
$$\left(\frac{\dot{a}}{a}\right)^2 = \frac{8 \pi G}{3} \frac{{\rho_{m,0}}}{a^3} - \frac{K}{a^2}$$
The Universe is initially only matter-dominated with no cosmological cons... |
I got this question after looking into transcendental numbers and I noticed how there are some distinctions that should be made from numbers and reality especially in measurement of length for example there are no perfect circles in reality and only exist in the mind and $\pi$, being a transcendental number doesn't act... |
Bayesian Estimation Approach for Quantum Phase Estimation:
I am interested if my understanding of the iterative method for Bayesian quantum phase estimation is correct before producing computational models thereof. Any comments, corrections and discussion will be appreciated, thanks.
Encode the true phase $\phi$ by so... |
What was the entropy of the universe a) during inflation; b) at the end of inflation (at reheating, begin of the big bang)?
|
Energy is not really defined formally in what it is but in how it changes
Energy is as a number we can assign to a system using certain
carefully chosen formulas and we state that this number is constant no
matter what change a closed system has gone through. And there are a
lot of formulas for seemingly different kin... |
How do I calculate the voltage v1 using KCL?
I don't understand how I should express the current I3 to get the equation right.
I already watched this video but I don't know what to do when there are two resistors. https://www.youtube.com/watch?v=BMnFC63m1fQ
|
What is the magnitude of electric field strength at the vertex of a uniformly charged cube of side 'a' and charge 'Q'?
Tried solving this by Gauss' law and by superposition but neither helped.
|
Regarding this experiment where a magnet is moved in and out of a coil -(see the picture)
what i considered to be true is that when there is a changing magnetic flux through the coil(due to changing magnetic field coz area and orientation of coil is kept constant), it produces a circular Electric field around the coil ... |
In the antiferromagnetic quantum Heisenberg model
\begin{equation}
H=J\sum_{\langle i,j\rangle} X_i X_j + Y_i Y_j +Z_i Z_j, ~~~(J>0)
\end{equation}
if the underlying interaction is biparitite, i.e. if all spin labels $i$ could be divided into two subsets $A$ and $B$, and interactions only appear between those two, we ... |
I am asking this question because different websites are saying different things the different answers I am seeing are $\frac{Q}{8\epsilon_0}, \frac{Q}{24\epsilon_0}, \frac{Q}{6\epsilon_0}$. I am hearing different arguments for each one but I can't decide which is correct. The first one is simple and appealing. Previou... |
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