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Is the cosmological redshift $z$ associated with the recession velocity when the light left, when it arrived, or something in-between?
|
I've searched a lot on the internet, but so far, nothing has been able to resolve my doubt completely. So here it goes,
We know that,
$ I = \vec J • \vec A $
So, $ J = \frac {I}{Acosθ} $
Now, consider θ = 90°
I = 0 (since the area vector and current density are perpendicular, ZERO current flows through the area).
B... |
Let there be a block of mass $M$ sitting on top of a table. there is a hole in the table right under the center of mass of the block.
A bullet of mass $m$ is shot through this hole and it hits the block and passes through it, losing some velocity.
The impulse imparted in the block due to the bullet passing through it i... |
Suppose we have a string (in tension) with its ends fixed. Think of a guitar string. Suppose we start with a plucked initial position and we let the string free. If we use the wave equation: $u_{tt}=c^2u_{xx}$ to predict the motion, then d'Alembert's solution is this.
In reality, when we pluck a guitar string, the moti... |
They make the following steps:
$$\int\frac{\Omega_\bf{k}}{4\pi}\ \frac{1}{(\hat{k}\cdot p')(\hat{k}\cdot p)} = \int_0^1d\xi\int\frac{\Omega_\bf{k}}{4\pi}\frac{1}{(\xi\ \hat{k}\cdot p'+(1-\xi)\ \hat{k}\cdot p)^2}=\int_0^1d\xi\frac{1}{(\xi\ p'+(1-\xi)\ p)^2}$$
In the first equality they use a Feynman parameter. I think... |
If I have two evacuated chambers each 10m on a side. Both are strong Vacuums but one is a slightly lower pressure than the other (A is the lowest pressure vacuum [ 10x-10 tor], B is the slightly higher pressure vacuum [10x-8 tor]).
When I open a connection between the two chambers, how quickly will they equalize?
It's ... |
The procedure to quantize free field theories is imposing a commutation/anticommutation relation with the field and its conjugate momentum, as $$\mathcal L = i\bar\psi\gamma^\mu\partial_\mu\psi\rightarrow\left\{ \psi(t,\vec x),i\psi^\dagger(t,\vec y)\right\}=i\delta(\vec x-\vec y)$$ But how would this procedure be appl... |
I'm currently working in a problem about formulating a Lagrangian for Newton-Cartan theory and i'm currently proving if it works.
In order to do this i'm required to compute the derivative of the Lagrangian w.r.t x
$ \frac{\partial L}{\partial x} $
As it appears in the first term of the Euler-Lagrange equation
$ \frac{... |
I have found the following exercise in one of my problem sheets:
Suppose we have an observable $Q$ and its corresponding operator $\hat{Q}$ has three eigenfunctions $\varphi_1, \varphi_2, \varphi_3$ with eigenvalues $2, 2,$ and $0$, respectively. Let $\psi$ be the following superposition state:
$$\psi(t=0) = \varphi_1... |
The radial wavefunctions of electrons in hydrogen atoms, the electron orbitals or "clouds," is a topic covered in almost any quantum mechanics course or textbook. Something that has always been curious about them to me, but that I have never found a good explanation of, is related to the axis of symmetry that some orbi... |
I have implemented a 2D finite difference method to compute the eddy currents induced by an AC magnetic field (homogeneous, oscillating at a fixed frequency) in a conductive thin sheet. Typically, the thickness of the sheet is around the half of the skin depth. Ultimately, the intent is to compute the impact the sheet... |
Let's assume that we have a flat object which has a random shape and does not have a symmetry axis. Let's assume the flat object lays in the xy-plane.
Any rigid body in principle has a set of three principal axes, which can be found generally by diagonalizing the matrix corresponding to the inertia tensor.
For this spe... |
I'm exploring the physical principles underlying diffraction and interference, specifically how these phenomena depend on the wavelength of harmonic (sinusoidal) components of a wave. My question centers on understanding why the wavelength of these harmonic components is crucial in determining the behavior of waves in ... |
I'm following my professor's notes on QFT, and I cannot understand this passage. It's about an infinitesimal transformation for the coordinates of a scalar field $\phi$. The passage reads:
Let us consider an infinitesimal spacetime translation $$x^{\nu} \to x^{' \nu} = x^{\nu} - \epsilon^{\nu}$$ whence
$$\phi_i (x) \... |
The mysterious York time, θ is important in warp drive topic. It is plotted on the famous diagrams and is considered the measure of the mechanism that "drives" the warp drive bubble at superluminal speed. However, the basic articles do not explain in detail what it is derived from and how it measures the expansion and... |
Watching Walter Lewin's classical mechanics. In lecture 11 he says when moving object up vertically distance h, the work done by gravity is -mgh, which makes sense. But then he said the work done by him is obviously mgh. Why is that the case? Doesn't the force he exerts need to be greater than mg in order to overcome t... |
I try to decomposite an arbitrary quantum state into a matrix product state. For this i follow this paper by U. Schollwöck where especially section 4.1.3 is relevant.
So far I did the following:
created a random vector $x \in \mathbb{C}^{2^L}$ and normalized it
reshaped it to $\sigma_1$,($\sigma_2$,$\sigma_3$...,$\sig... |
If $y1=Asin(kx-wt)$, it is identical with $y2=-Asin(wt-kx)$.
But then if I write a reflected equation of y1, it is -Asin(kx+wt), whereas the reflected equation for y2 becomes Asin(wt+kx) since both the phase and direction of motion get changed at the fixed end.
But how can the same wave equations y1 and y2 end up in di... |
I'm studying calculus of variations and Lagrangian mechanics and i don't understand something about the variational operator
Let's say for example that i got a Lagrangian $L [x(t), \dot{x}(t), t] $ which is a functional of a position function $ x(t) $ its derivatives and time.
If i take the variation of the Lagrangian ... |
This is somewhat of a follow-up question to my previous question on the Dirac-Hestenes equation. In that question, I asked whether the equation could be written in a form that omits the dangling indices.
Context
In free space, using natural units, the Dirac-Hestenes equation takes the form
$$
\vec{\nabla} \psi I \sigma... |
While studying E&M, I came across the force density for the electromagnetic field $\textbf f$. The following is the expression for the same
$$\textbf f = -\frac{1}{2}\nabla\left(\epsilon_0E^2+\frac{1}{\mu_0}B^2\right) - \epsilon_0\frac{\partial}{\partial t}(E\times B)$$
If we express it in terms of the energy density o... |
Background
I have simulated a vibrating viscoelastic string fixed at each end under tension using finite difference modeling. Most simply this can be done using Kelvin-Voigt style mass-spring dampers as the units such as these:
Where for each unit stress in terms of strain is described as $σ = Eε + ηε_t$.
This works w... |
I understand that an electron in orbit is technically entangled with the nucleus. Is an electron with higher energy (further away from the nucleus) less entangled with the nucleus? Does a free electron remain partially entangled with the parent nucleus?
|
Quoting from Prof. Leishman's book on Helicopter aerodynamics, the centrifugal force acting along the blade is calculated as below.
My intuition is, not only the mass of the small blade element $dy$ is relevant here but also the section of the blade ahead of the blade element $dy$ is important to taken in to account a... |
In the unbiased PN junction the electric Field inside the depletion region is just due to the fixed charges inside it
But what happens in case of reverse
basing ?
In case of reverse bias the reverse electric Field due to the battery widen the depletion region which Create more charges in it and hence increase the fiel... |
In this recent paper, Bousso and Penington (B&P) finds that the protrusion distance outside the horizon of an entanglement island from a 4D Schwarzschild black hole is $\sqrt {l_P r_{hor}}$, where $r_{hor}$ is the Schwarzschild radius of the BH and $l_p$ is the Planck length.
This result is a geometric mean, and is exa... |
How do curved soap films remain in equilibrium, if surface tension tries to pull them taut?
What I understand:
Surface tension acts tangentially on a surface.
The potential is energy is proportional to surface area, hence the film tries to minimise it's surface area
From this Libretexts article I learnt how to find th... |
We know that when we heat bimetallic strip it bends. But I can't understand what force causes it to bend.
Like, suppose they are attached by a nail passing through them. Now, when the strip is heated, the metal with higher coefficient of linear expansion(α) tries to expand itself linearly. Meanwhile, the metal with low... |
Are there any systems we know of whose partition function is not simply Wick rotation of the path integral? Does anyone know of any examples?
|
I'm having trouble understanding the rules for dimensional and dimensionless constants. In dimensional analysis, you can only add or subtract quantities with the same dimension. For example, if $f=12t+2t^2$, then $12=\frac{[f]}{[t]}$ and $2=\frac{[f]}{[t]^2}$ are dimensional constants.
However, another rule I've come a... |
I've read the Green function derivation for Poisson Equation (electrostatics) in this document. There are some points which are not clear for me.
On page 10, the document starts with the Poisson Equation involving the Green Function:
$$\nabla^2 G(\textbf x - \textbf x_0) = \delta(\textbf x - \textbf x_0)$$
where $\text... |
I have a passive optical cavity used as an OPO for the generation of squeezed states in pulsed regime, schematized in the following figure.
The crystal used to generate squeezing is a KDP (C1), which type-II phase matching produces a signal and an idler on two orthogonal polarizations (horizontal and vertical). In the... |
When impurities like salt is added to water, the boiling point of water increases because of what I think is vapour pressure, though I know very little about that too. However, with the same analogy, the freezing point should also increase. Instead, it decreases. Then why does it have to be added to ice-creams? Some we... |
From the Lagrangian in Maxwell theory
$$L = -\frac{1}{2}(\partial_{\mu} A_{\nu})(\partial^{\mu} A^{\nu}) + \frac{1}{2}(\partial_{\mu}A^{\mu})^2 - A_{\mu}J^{\mu}$$
I have to calculate $\frac{\partial L}{\partial (\partial_{\mu}A_{\nu})}$.
I understood that
$$\frac{\partial }{\partial (\partial_{\mu}A_{\nu})}\left(-\frac... |
I am having trouble while solving in the Problem 3.1 of the QFT book by Schwartz.
Problem
Find the generalization of the Euler-Lagrange equations for general higher-order Lagrangians of the form $\mathcal{L}[\phi, \partial_\mu \phi, \partial_\mu \partial_\nu \phi, \ldots]$.
I have tried to solve this problem. But got s... |
I'm self-studying the 3rd edition of Jackson's Classical Electrodynamics and I have a question about a problem. The fifth problem of Chapter 1 asks the reader to determine the volume charge distribution giving rise to the potential
\begin{equation*}
\Phi = \frac{q}{4\pi \varepsilon_{0}}\frac{e^{-\alpha r}}{r}\left(1+\f... |
In his book "Fashion, Faith, and Fantasy in the New Physics of the Universe" Sir Roger Penrose mention ( referring to his older works and specially Penrose-Hawking Theorem) the possibility that compactified string theory have to be unstable. Especially PFDoF related to high dimensionality of physical spacetime have nec... |
All airfoils I have seen become narrow towards the trailing edge.
Is it still possible to create a forward vector force if the shape becomes wider again after a narrow middle section?
I read that the air flows around the airfoil and that that is part of the dynamic that creates the upward and forward force. Is this ess... |
I know that molecules can spin around a central axis, but lately I keep wondering if it is possible for a single atom to spin around its own axis (like earth for example). Also does this concept of the orientation of a single atom actually exists?
|
Is gravity just geometry why is there no anti-gravity or repulsive gravity based on the solution to Einstein's equations?
|
Imagine that you could put your hand out of a spaceship whilst it was travelling and it wouldn't get injured. What would the sensation be like? Would you feel anything, or would you not be able to tell that you were moving? If there are no particles then surely you wouldn't bash into anything to create a sensation?
|
Imagine that I have a methacrylate capsule filled with water (8cm in diameter and 30cm in length). If I wanted to measure the temperature with a laser thermometer pointing at the capsule, what temperature would it be giving me? Would it simply measure the surface temperature, would it penetrate the medium giving me the... |
Why the voltage across the Load resistor $R_L$ remains constant at 0.7 volts as long as the diode is forward biased?
Both diode and load resistor are parallel so the voltage across them should be equal but why 0.7 volts always? Shouldn't the out put voltage change as the source voltage change across the diode and resis... |
For the complex Klein-Gordon Lagrangian density in the non-relativistic limit, we can decompose the complex scalar field into the form $$\phi=\frac{1}{\sqrt{2m}}e^{-imt}\psi.$$ When substituting the explicit form of $\phi$ into the lagrangian density, you end up with this term:
$$L=\frac{i}{2}\psi^*\dot{\psi}-
\frac{i}... |
I am currently working on an exercise involving the discretized version of Schrödinger's equation in an infinite potential well. The problem involves a well with a width of 1 and assumes $$\frac{\hbar}{2m} = 1$$ for simplification.
The exercise requires solving the following differential equation:
$$\frac{d\tilde{\psi}... |
As we know that 1st process is an reversible isothermal expansion during this the system is in quasi static equilibrium which helps in increasing the volume of the system but why does the second step need an adiabatic expansion like why do we need an second step as the heat absorbed is equal to the work produced
|
We consider a two-level system with a ground state $|g\rangle$ and an excited state $|e\rangle$. It is placed at position $\mathbf{r}$ and driven by a coherent field $\mathbf{E}$. Assuming a dissipative system and choosing $\hbar = 1$, the Heisenberg equation reads
$$i \partial_t A = [A, H] + i\mathcal{L[A]},$$
with th... |
Based on the Hall optical conductivity graph, how can we tell if we have ordinary or anomalous Hall conductivity?
|
I want to calculate multiparticle states like $|\vec p,\vec p\rangle$ from $|0\rangle$. It seems that I would need to compute from things like: $a^{\dagger}_{\vec p}a^{\dagger}_{\vec p}|0\rangle$?
It seems to me that the first should yield a multiparticle state such as $|\vec p,\vec p\rangle$, i.e. two bosons in the mo... |
The text I am reading (Peskin and Schroeder) gives the Hamiltonian for the free Klein-Gordon field as:
$$H=\int {d^3 p\over (2\pi)^3}\; E_p\; a^{\dagger}_{\vec p}a_{\vec p}$$
This does not seem to be good for multi-particle states. How would this Hamiltonian be modified for multi-particle states?
|
Due to metamerism, many different light spectra can be used to show a white colour.
If I understand it correctly, it is even possible to make white light by combining only two monochromatic light sources, for example 440 nm and 570 nm.
Displays often have three primaries (red, green and blue), and if these are monochro... |
I am investigating the relationship between the moment of inertia of a yoyo-like apparatus (maxwell's wheel) and its damping coeff. I am adding disks to my yoyo to change its moment of inertia, which incidentally also changes its weight.
As the moment of inertia increases, the damping coeff. decreases, and up to a cert... |
I've come to understand "calculus" as the mathematical study of continuous changes in a mathematical function or physical system. Differential and integral calculus are broad examples of this.
R.C. Jones studied transformations of an optical polarization state, and called the vector/matrix operations a "calculus" [1]. ... |
Say you have a convex lens with one of the sides completely coated with a mirror like substance, effectively rendering one side into a mirror. How would this lens work? Would the usual formulas like $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$ or $\frac{1}{f} = (n-1)(\frac{1}{R_1} + \frac{1}{R_2})$ still apply?
|
Imagine a planet with the same properties as Earth, this time moving in an elliptical orbit around a black hole of a large number of solar masses. Also imagine that the surface of this planet is as massive as that of the Earth and that you can therefore experience a normal force on it as on the Earth's surface. At a sp... |
For any $\epsilon >0$, consider the following harmonic oscillator with $m= \hbar =1$:
\begin{equation}
\frac{\partial}{\partial t}\psi(x,t)= -\frac{1}{2}\Delta \psi+ \frac{\epsilon}{2}x^2 \psi
\end{equation}
where $x \in \mathbb{R}$ and $t$ is time.
Then, I wonder if solutions of the above Schrodinger equation converge... |
In this answer, it says : "At small Mach numbers, changes in speed cause negligible changes in density, but as Mach approaches unity, both are of similar magnitude. With Ma>>1 , changes in density will become dominant. A speed increase is always coupled to a decrease in density."
Why does the density decrease equal the... |
A rocket engine in the vacuum will experience efficiency loss due to under-expansion in which the pressure of the exhaust is greater than the ambient pressure, which in a vacuum is near zero.
How great is this efficiency loss in real-world terms? The thrust equation has a term in which the ambient pressure is subtracte... |
I am trying to better understand one of my previous questions, and another.
Charged particle in uniform Magnetic field
Does a charged particle orbiting Earth radiate?
https://en.wikipedia.org/wiki/Paradox_of_radiation_of_charged_particles_in_a_gravitational_field
To the extent I understand the answers, it seems to me t... |
When 2 black holes approach each other, they both bend space in an opposite direction. There must always be a flat space between 2 colliding black holes.
However, I heard that they actually merge, becoming one...
I wondered, how can this happen?
Also, is it a good way to get very-very close to the center of a black hol... |
It is often said in quantum field theory books that a quantum theory of fields is needed because every other attempt to develop a quantum-mechanical theory compatible with the principles of relativity was flawed. The prototype example is the attempt of obtaining a Schrödinger equation describing a relativistic particle... |
In the Liquid Drop Model of the nucleus, the most stable isobar is the one whose atomic number $Z_{A}$ is the one corresponding to the minimum mass, and can be found from the mass parabola or, by differentiating the mass equation with respect to $Z$, using the following final formula:
$$Z_{A}= \frac{\frac{A}{2}(1+\frac... |
Goal
I am trying to solve a wave equation of motion for the transverse vibrations of a viscoelastic string fixed at each end to get the $Q$ (decay rate) of each harmonic (partial).
The goal is to allow approximate simulation of the vibrating string with a series of damped harmonic oscillators (one for each harmonic) wh... |
I've always heard that when protons and neutrons are combined together into nuclei, the mass of the product is less than the mass of the constituents. And that this mass is called the mass deficit and attributed to the loss in potential energy and sometimes (depending on source) considered equivalent to the binding ene... |
I've heard that the reason we don't see quantum effects at the macroscopic level is because of decoherence.
But I don't know what quantum effects at the macroscopic level would even look like... So I don't understand what exactly decoherence is preventing from happening at the macroscopic level.... what exactly does "i... |
One basic difficulty in QCD is that it does not contain a small dimensionless quantity that would allow for perturbative calculation of low-energy observables.
A remarkable feature of holographic dualities is that in many cases one description of the
physics is strongly coupled, while the dual description is weakly cou... |
I am reading some papers related to charge density waves in 1T-TaS2 or 1T-TaSe2, which are among the most studied systems with CDW and strong correlations.
I checked the definition: A CDW is commensurate if and only if the wave vector describing the CDW is a rational number times one of the vectors that make up the Rec... |
Without considering gauge invariance, A.Zee derives Green function of electromagnetic field in his famous book, Quantum Field Theory in Nutshell. In chapter I.5, the Proca action would be,
$$S(A) = \int{d^{4}x\,\left\{\frac{1}{2}A_{\mu}\left[(\partial^2+m^2)g^{\mu\nu}-\partial^{\mu}\partial^{\nu}\right]A_{\nu}+A_{\mu}J... |
An example could be found on this pdf file and the discussion was the 2d conformal transformation. Usually, the conformal transformation was derived locally such that the local conformal transformations are the space of (the all) holomorphic functions
$$f(z).$$
However, for the global conformal transformation, the (Di ... |
While reading about volumetric stress, I found that volumetric stress on a body is equal to restoring force per unit area if force is normal to the surface and is proportional to the area.
At equilibrium,
So Volumetric stress should be equal to external force per unit area.
So if we add extra force and change the press... |
I mean I get people saying because it's Newtonian mechanics. Everything inside the train will have same speed as that of train but my question is why ? Why is it like that ? And How does that happen ?
Even if you say that let's say you and train kind of like become a system if you're let's say like sitting in the train... |
I'm following Schutz's General Relativity book and I am confused about his description and derivations of a spherically symmetric spacetime. I searched online and found that using Killing vectors is a common approach. It is unfortunately not (yet) part of Schutz' reasoning, so I don't yet quite understand that methodol... |
I would think, that the green light is blocked and the red light travels through the glass undisturbed. Therefore what you see is a red beam, but no green beam after the glass.
'Blocking the green light' means: the green light interacts with the electrons in the red glass, bringing them to a higher energy level, and th... |
Background
I am using resonant bandpass filters as musical oscillators. One can excite an array of them at harmonic frequencies and given Q values for a note by, for example, running a burst of noise through them.
I thought intuitively that an array of damped mass-spring oscillators tuned to the same Q and frequencies ... |
What are Fermi levels in the context of 2-d electron fluids and specifically the Quantum Hall effect?
|
As far as we know:
If two one-dimensional lines are placed parallel, they need to be on a two-dimensional plane.
If two 2-dimensional planes are placed parallel, they need to be in a 3-dimensional space.
So is our space a 4-dimensional space because we (3-dimensional objects) can be placed parallel? (or am I misunderst... |
I was working on a problem that goes like this
Bob beats Judy by 10 m in a 100-m dash. Bob, claiming to give Judy an
equal chance, agrees to race her again but to start from 10 m behind the
starting line. Does this really give Judy an equal chance?( Assuming no acceleration and constant velocity).
After you make some... |
Topological order is defined to be a phase that has ground state degeneracy (GSD) not described by the Landau SSB paradigm but exhibits some Long Range Entanglement property. Mathematically, it is defined to be a tensor category.
My question is: can we define topological order in QFT, especially SUSY field theories and... |
I am studying Griffiths' introduction to electrodynamics and I struggle to understand the field of application of $$\int{D \cdot dA}=Q_{f_{enc}}.$$ Griffiths states that this law holds within dielectrics. Is $Q_{f_{enc}}$ the free charge inside the dielectrics (if so, could you please explain me what is the sense of ha... |
I'm in North Dakota, and over the last several years, I've noticed a trend. Whenever we have a cold snap (the weather gets below 0 degrees F), my apartment stays relatively warm (68-70 degrees F). But when the cold snap ends (the temperature goes back up to 5-10 degrees F, or even higher), the temperature in the apartm... |
Consider a closed FRW universe with proper radius of curvature $R$ filled with a fluid with mass density $\rho$ and pressure $P$.
Let us assume that the total force acting on the spherical boundary around us at radius $R$ is given by the fundamental maximum force in general relativity:
$$4\pi R^2\ P = -\frac{c^4}{G}.\t... |
Consider a lift(or an elevator, as Americans call it) which has a block in it, with the lift accelerating upwards. We are looking at this system from the ground frame.
Wouldn't the block's net acceleration be (g-a), as gravity is acting downwards, whereas the lift's acceleration is upward?
Similarly, when the lift acce... |
At work we faced the following problem:
We are working with some high voltage batteries which are located inside a casing which isolates the batteries. This means you cannot get any significant current by short circuting the batteries by using the casing.
The production teams, hoewever faces problems. When touching th... |
Context
I read the note Light Cone Quantization and Perturbationwritten by Guillance Beuf. He gives a argument in section 3.3.2, p17, 2nd paragraph :
In particular, in a theory with a mass gap, excitations above the ground state obey $2k^{+}k^- \geq m_{gap}^2 + \mathbf{k}^2> 0$. Hence, there is no excitation of finite... |
If I understand correctly, there is energy bound in a gravitational field, although acceleration of the body that causes the field is required to release some of that energy (in the form of gravitational waves).
Is there a fixed relation between the energy of an object and the energy contained in the gravitational fiel... |
If a system contains isotropic exchange interaction and uniaxial anisotropy in the $z$-direction,
does this Hamiltonian satisfy rotational invariance of the $z$-direction so that the spin angular momentum in the $z$-direction is conserved?Is the spin angular momentum in the x,y-direction not conserved because it does ... |
Just got an introduction to statistical mechanics in my thermodynamics class. I understand the concept of macrostates and microstates as the following:
A macrostate is some kind of restriction on all the possible microstates making a finite set of microstates that follow that restriction.
My question is on how free I a... |
In classical mechanics, the action of a theory is determined by its Lagrangian:
$$S(q) := \int L(q(t),\dot{q}(t),t)dt $$
In the following, let us assume that $L$ does not depend explicitly on time. Note that the Lagrangian is a function $L: \mathbb{R}^{n}\times \mathbb{R}^{n} \to \mathbb{R}$. The Legendre transform of ... |
About the saturation region of common emitter Bjt it's written that
In saturation mode both of the "diodes" in the transistor are forward biased. That means V(BE) must be greater than 0, and so must V(BC). In other words, V(B) must be higher than both V(E) and V(C).
I wonder that if V(B) is at a higher potential than V... |
for shift in a image from its original position due to a slab of thickness $t$ and refractive index $u$ is given by $shift(s)=t[1-1/u]$
and for shift in fringes formed during youngs double slit experiment, the shift is given by
$s=[u-1]tD/d$
where $d$ is fringe distance, $D$ is distance between fringes and sheet.
$D... |
Suppose you connect two wires with different resistances to form a single wire. When you apply a voltage, a current will flow. Do the electrons in the wire with smaller resistance move with a higher drift velocity compared to the wire with higher resistance? Obviously, both carry the same current, but this could be exp... |
I was interested in seeing if I could derive the mean free path of an "air molecule" by considering the reference frame of an individual molecule as other particles moved around it randomly. This is sort of the opposite of the simple model of a moving beam through a slab of stationary particles. My approach strikes me ... |
As per my knowledge bodies attain constant temperature (thermal equilibrium with surroundings) when they absorb and emit energy at equal rates.
Let us say temperature of surroundings is T1.
We have a large collection of bodies at a temp T2 (different from T1) with equal emmisivities and with different coefficient of ab... |
I'm confused about how conductors work.
So, imagine we have a spherical conductor, charged with a certain potential, $V$, that must remain constant.
Now, this sphere has a cavity inside, where we put a certain charge $q_1$.
I guess, since the electric field must be $0$ inside the conductor, charges will rearrange in su... |
Physically, propagator represents the probability amplitude of a particle to travel from one point to another. But the photon propagator $$D_{\mu\nu}(x,y) = \langle 0 | \mathcal{T}[A_\mu(x) A_\nu(y)] | 0\rangle$$ is a second rank tensor quantity, whereas probability amplitude is a scalar quantity! So
What does the $(... |
If you are given, (or found) the position and velocity vectors of an asteroid how can one use this to predict its orbit?
|
I got this answer to my last post,
See answer.
That raises another question, then. Knowing $\nabla\cdot\vec{E}=\frac{\rho}{\epsilon _0}$, then $\rho$ should be $0$ (because $\vec{E}=0$). But it's not, since we agreed there is a distribution inside the sphere. Isn't that weird?
Maybe the only charge distribution lies on... |
I am thinking about ohms relationship $E = j\sigma$, where $\sigma$ is entirely material-dependent, which can be explained by Drudes model and the common explanation that surface charges create the E-field inside a wire.
Imagine a high $\sigma$ wire and a low $\sigma$ resistor with same form and size (their area is the... |
I am trying to better understand the meaning of various spin susceptibility functions used in condensed matter physics especially in neutron scattering experiments.
In the following definitions, $\omega$ represents Matsubara frequencies, $\tau$ is imaginary time and subscripts $i,j$ represent the lattice site :
Dynami... |
Along the geodesic of a stationary observer in Minkowski spacetime we have the following tangent vector
$$t^\mu = (1,0,0,0)$$
We have that hypersurfaces of constant time along this are just 3D Euclidean spaces.
I need to calculate the trace of the extrinsic curvature of these hypersurfaces and since the tangent is orth... |
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