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Assume that we have a cohomological field theory, with an odd symmetry generated by an odd operator $Q$ and an exact energy momentum tensor $T_{\mu\nu}=[Q,G_{\mu\nu}]$. Then by integrating over an spatial slice we define $G_\mu=\int d^3\vec{x} G_{0\mu}$, so that $P_\mu=[Q,G_\mu]$. The first claim is that if $\mathcal{O... |
Consider an object of radius $R$ traveling at a constant, slightly subsonic or supersonic speed through a homogeneous fluid, in conditions of very high Reynolds number. Because the object experiences a drag force, the power required to maintain its speed is
$$P = F v = \frac12 \rho C_D A v^3.$$
By energy conservation, ... |
Question: Water from a hose is spraying at a skateboard (3 kg), pushing the skateboard forward.
The water comes out of the hose at a rate of 100 grams per second, with a speed of
4 m/s. Assume the water sticks to the skateboard and very slowly runs off (so ignore
any change of mass of the skateboard due to collecting w... |
In a semiconductor when there is a depletion region electrons can't flow through this and acts as an insulator. This depletion region can expand when a battery is plugged a certain way. Why can't charge travel through this depletion region?
My second question is when electrons enter the p-side of the semi-conductor the... |
I'm trying to build a tennis ball machine and I'm using a couple resources to help me out. One of them has the following formula for calculating drag force which I am having trouble interpreting.
The main question I have is what the V with a bar means and the difference between it and the regular V. I am also wonderin... |
I have a question about an intuitive approach to spinors as certain mathematical
objects which have properties that make them similar to vectors but on the
other hand properties which differ them from vectors:
Wiki gives a rather geometrical description of a spinor:
"Unlike vectors and tensors, a spinor transforms to ... |
In the comments of OP What is spontaneous symmetry breaking in QUANTUM systems?
There is a statement by OP Xiao-Gang Wen saying "the ground state of transverse Ising model $$=−∑__+∑_$$ of spins. For small , the exact ground state still do not break the →− symmetry. So it is non-trivial to see the $$→−$$ symmetry break... |
I have a function $f(x) = \exp(-\frac{x^2}{\sigma^2})$ on a box of size $L$. I have the given relation between the size of the box and the width of the Gaussian $\sigma = \sqrt{\frac{2}{\pi}}L$. I use the following definition for the Fourier coefficients:
$$c_n = \frac{1}{2L}\int_{-L}^L \exp(-\frac{x^2}{\sigma^2})\exp(... |
I have a question about computing the far field diffraction pattern of a laser beam:
If $L_{1}$ is large enough, then at $z=L_{1}$ we see the Fourier transform of the input $f(x, y)$. If $L_{2}$ is large enough, we see the Fourier transform of the input image at $z=L_{1}$ (the Fourier transform ${\cal F}$ of
$f(x,y)$).... |
Let's start with a single particle Hilbert space $H$ with basis $\{|\alpha\rangle\}$, where $\alpha$ represents a complete set of quantum numbers. If we now take two particles of the same type, we must consider the space $$H_2=H_1\otimes H_1,$$ and more generally $n$ particles live in $$H^{\otimes n}=H_1\otimes...\otim... |
When spraying water, why does the end of the garden hose have a force opposite to the direction of the water flow? I'm talking about the kind of hose without a nozzle. The hose is of equal diameter from beginning to end. The water should not accelerate in it, so there should be no opposing force at the end of the hose.... |
Alright, so I'm trying to understand in detail what occurs the moment the water covers the outlet tube in a bell siphon. Most sources hand wave and just say "SIPHON HAS OCCURED" or "VACOOOOOOM", but what specifically causes the formation of the vacuum or siphon effect.
If the air in the bell is at 1 ATM the second the... |
What is the physical interpretation (if there any) of angular displacement as a vector?
I personally used the right hand palm or screw rule to find out the direction but it has been just a rule for me to solve problems rather understanding the exact occurence or system, it has been remained as a unassuming fact for me... |
Is there a similar version of the summation theorem for spherical Bessel functions $j_{k}$ that of standard Bessel function $J_{k}$? Especially look below Eq.(3) in this paper https://arxiv.org/abs/cond-mat/0510271 for $J_{0}\left(\left|p-p'\right|r\right)$.
$$J_{0}\left(\left|\vec{p}-\vec{p'}\right|r\right)=\sum_{k=-\... |
I found in tables that the experimental energy required to brake the bond of the hydrogen molecule H$_2$ corresponds to $E=436$ kJ/mol. So I wanted to convert this value to temperature using the relation $E=k_bT$. The temperature corresponding to that energy is $T= 51~960$ K. This is roughly 9 times the temperature of ... |
Let us consider the worldline $x^\mu(\lambda)$ of an observer moving in an arbitrary manner (i.e. possibly non-inertial). If we want to write down the proper time interval measured by that observer between two points $\lambda_1$ and $\lambda_2$ on its trajectory, we use the formula $$\Delta\tau=\int\limits_{\lambda_1}^... |
I am learning QFT. Earlier we showed that a complex field can be decomposed like so:
$$\begin{align*} \phi &= \int \frac{d^3k}{(2\pi)^3}\frac{1}{\sqrt{2\omega_k}}\big(a(\mathbf{k})e^{-ikx}+b^\dagger(\mathbf{k})e^{ikx}\big) \\ \phi^\dagger &= \int \frac{d^3k}{(2\pi)^3}\frac{1}{\sqrt{2\omega_k}}\big(b(\mathbf{k})e^{-ikx}... |
I have searched PSE (and many other sites on internet) for the theoretical reason of induced emf. All I got was that the phenomenon of Induced EMF is experimental fact and can only be mathematically understood using Maxwell's equations.
For the last few days I have thinking about it and I found an analogy and would lik... |
I have two questions about the $Symmetrization \ Postulate$:
In a system with $N$ identical particles, physical states aren't arbitrary states in $V^{\otimes n}$. Rather, they're totally symmetric (belong to $Sym^NV$), in which case the particles are said to be bosons, or they're totally anti-symmetric (belong to $Ant... |
What is topological in Kitaev Chain? Realspace or the space of Pauli spins or the space of fermions?
My Understanding
I understand that majorana-zero modes are which are spatially separated, are protected in one phase. I am confused with the very notion of 'topology'! When talking about topology people show donut and c... |
Some years ago I bought a duvet which said "[This duvet] is designed to keep you cool in summer and cosy throughout winter". I didn't think much about it at the time because it seemed like typical advertising bluster, but then after using the duvet it's become apparent that it actually works. I need to wrap the duvet t... |
Do wires with DC current vibrate like wires with AC current (very tiny vibrations)?
|
The standard equation for any object moving in a linear simple harmonic motion (SHM) is
$$x=A\sin(\omega t +\delta)$$
where $A$ is the amplitude, $\omega$ is the angular velocity.
Likewise, converting the linear variables in the above equation to angular variables, we get the equation of angular SHM as
$$\theta =\theta... |
I am currently experimenting with a homemade Van de Graaff generator. The design looks just like in the Wikipedia page here. In many designs of the VDG, I see that the bottom comb is connected to a metal sphere. The Wikipedia page said that it is also connected to the ground.
In the example, the wand with metal spher... |
In Griffiths electrodynamics example 3.3 we've to find potential in a region subject to the conditions
(i) $\quad V=0$ when $y=0$
(ii) $V=0$ when $y=a$
(iii) $V=V_{0}(y)$ when $x=0$
(iv) $V \rightarrow 0$ as $x \rightarrow \infty$
And the example goes on to solve it.
My question: Any point on the z axis has coordina... |
In a linear process with an ideal gas, given by $p(V)=p_0-\alpha V$ ($p$ - pressure, $V$ - volume) in the $pV$ coordinates, the quantity of energy ($Q=ΔU+W$) transfered between point $A$ (with the highest temperature) and an arbitrary point $B$, both on the $p(V)$ graph, reaches its maximum when $B$ is the point of tan... |
I came across this problem in the book "Problems in General Physics by IE Irodov"-
Three points are located at the vertices of an equilateral triangle whose side equals s. They all start moving simultaneously with velocity v constant in modulus, with the first point heading continually for the second, the second for t... |
The masses of protons and neutrons are different. Suppose a proton is a sphere with a uniformly positive charge distribution. Can the mass difference between protons and neutrons be due to the electrical potential energy of the protons? Justify your answer with a simple calculation.
I do not really know the relationshi... |
I can find this term stated both ways in different literature.
Are they equivalent?
It's weird because the dot is a dot product in (u⋅∇), but ∇u being a gradient of a vector field, would (presumably) produce a (jacobian?) matrix which would turn that dot-product dot into a regular vector-matrix multiply where I have to... |
I found it very instructive to see how the $E$-$k$ relationship of a free particle can be roughly identified from the extended band structure of a solid: The following is the outcome of the one dimensional Kronig–Penney model.
For three dimensions things get more complicated. Lets have a look on Si:
Taking only the 1... |
I'd like to apologies in advance for the horrible diagram, my question is regarding the following situation:
Consider a circular loop of wire placed within an external magnetic field; this field varies with time and is given by the following expression: $$\vec{B} = B_{0}f(t) \hat{k}$$ Given that the circle has a radi... |
Consider the Hamiltonian for a System of $N$ anharmonic oscillators
$H= \sum_{i = 1}^N (\frac{p_i^2}{2m_i}+\frac{1}{2}k_iq_i^2)+\sum_{i,j=1}^N b_{ijk}q_iq_jq_k$
with specific constants $k_i,b_{ijk}, m_i$ and the respective Positions $q_i$ and Momenta $p_i$. The equilibria of the system are the Solutions of the equation... |
In section 4 of this article, suppose we have $N$ particles of the same mass $m$ moving in one dimension and interacting with each other via the potential $V_{ij}\equiv V(x_i - x_j)$, where $x_i$ denotes the position of the $i$-th particle. Because the total momentum
$$
I_1 = m\sum_i \dot{x}_i
$$
and energy
$$
E = \fra... |
I drew sort of a picture down below (although the cell is supposed to be an ac supply). I don't understand which direction the magnetic flux?
This is because, the current-carrying wire has individual magnetic fields (using the right hand grip rule) and so I am confused with how you tell in which direction the magnetic... |
To each observable in quantum mechanics there is an operator corresponding to it. I don't understand what's the meaning of the eigenvalues of the $\hat{x}$ operator. Since $\hat{x}$ is hermitian, eigenvalues correspond to real numbers, what's their physical meaning? If they describe a particle localized at a particular... |
Consider the first law of thermodynamics,
$$ dU = dq +dw$$
simplfying,
$$ dU + P_{\text{ext}} dV = dq$$
Now we can say that $ q $ is a function of $ U$ and $V$
$ dq(U,V) = dU + P_{\text{ext}} dV$
For a differential $dF(x,y) = A\, dx + B\, dy $ to be exact,
$$ \frac{\partial A}{\partial y} = \frac{\partial B}{\partial ... |
So, I read, that the Casimir effect arises from the ground state of the electromagnetic field. But I don't understand where the electromagnetic field in the Casimir effect comes from, since we are considering neutral metallic plates.
|
You know the strong force (the one that keeps quarks together). Well it works by exchanging gluons right?
So how does that force keep the quarks together? I mean you can imagine that process as three people passing balls between them right? Well as far as I know that throwing of the ball wouldn't force those 3 persons ... |
Look at this photo taken in France during the 1999 solar eclipse which I found on Wikipedia. Why does the corona appear white? It has a temperature of about $10^6\,$K so you would think that it would maybe look more like violet?
|
Does the following functional derivative can be evaluated?
$$ \frac{\partial}{\partial(\partial_\mu \phi(x))} \int d^4y F(y) \partial_\nu\partial^\nu\phi(y)$$
I am trying to find the equations of motion of a classical field with a Lagrangian that has the form:
$$\mathcal{L}(\phi,\partial_\mu\phi)+\int d^4y F(y) \partia... |
Suppose it is convenient to construct a system of units so that all quantities can be expressed in terms of only one physical quantity. In one such system, dimensions of different quantities are given in terms of a quantity X as follow:
[position]=[$X^\alpha$], [speed]=[$X^\beta$],[acceleration]=[$X^p$], [linear momen... |
In Hobson's General Relativity book, pg. 125, it says that an instantaneous rest frame $S'$ can be defined for an accelerating observer in frame $S$ such that the observer is momentarily at rest in $S'$.
It also says
since the observer is at rest in $S'$, the timelike basis vector $\textbf{e}'_0 $ of this frame must b... |
Let's imagine a tube that is open at one end and is filled with water. A constant source of heat is applied to a specific spot somewhere at the middle of the tube, for a example a preheated soldering iron of constant temperature. Let's say you measure the temperature of water at the upper end of the tube over a specifi... |
If we launch a spaceship at relativistic speeds, the time on the spaceship, compared with Earth's, will pass slower. After a year on the spaceship, on Earth could have passed several years. And, if the spaceship reaches the speed of light, it would appear stopped in time from Earth's perspective. Assuming we could meas... |
One popular form of the equivalence principle states that the effects of a gravitational field in a small enough region of spacetime are indistinguishable from those of being in a uniformly accelerating frame. I interpret this statement as whenever we have a constant gravitational field, we can replace that situation w... |
I apologize to ask, again and again, a question that seems to come back often, but I believe this is new.
I am trying to test the equivalence principle applied to two similar situations:
Flat spacetime. An inertial observer Alice (equiped with a set of coordinates ($x$,$t$)) is watching a non-inertial observer Bob (pr... |
I was wondering if quantum particles do actually exists in two different states simultaneously and if it has been proven they do indeed exists in a superposition of states.
How has it been figured out since observing it would collapse the wave-function into one single state (two superposition of states into one ) as ... |
In my physics book "Fundamentals of Physics" by Jearl Walker there is a figure that shows a U-tube with uniform cross-sectional area. The U-tube contains two liquids in static equilibrium: water in the right arm and oil in the left. $l$ is 135mm and $d$ is 12.3mm (see image). My book says that liquids are in static equ... |
A uniform electric field can be set up as shown:
The force for a given charge will be constant anywhere in this field. However, as the distance from the charge to the oppositely charged plate decreases, the potential difference also decreases. This explains why force remains constant, as electric field strength is vol... |
Imagine a horse is tethered to a cart. According to Newton's third law, when the horse pulls on the cart, the cart will also pull backwards on the horse. Since the two objects are attached together, they are technically the same object, and they cannot accelerate.
This doesn't make any sense. In the real world, horse c... |
For a spherically symmetric wavefunction the probability is proportional to $|\Psi|^2r^2$, and if the wave function blows up at $r=0$ then at $r=0$ $|\Psi|^2=\infty$, and $r^2=0$ meaning that the probability is proportional to $\infty*0$ and on its own $\infty*0$ would be indeterminate, however for a continuous probabi... |
The drag force opposes the direction of velocity, and the lift force is perpendicular to both the drag force and the rotation direction.
So if a tennis ball is rotating clockwise and moving to the left with velocity v, the drag force is acting to the right, and the lift force is acting downwards since for clockwise rot... |
Imagine that we could do QFT calculations with a Hamiltonian that takes GR into account.
What is a relatively simple calculation that could show that this theory is more accurate than a "normal" QFT?
I'm thinking something along the lines of:
The scattering process of an electron and a positron should, with respect to ... |
In this note of Leonard Susskind's GR course, he considered two different frames $z$ and $z'$. The $z$-frame is attached to the earth and the $z'$-frames moves up with an acceleration $g$. See equations $(1)$ and $(7)$.
In general relativity, we learn that a coordinate system attached to the earth is like an accelerati... |
In exercise 12.1 tells the relation between $N_2$, the number of M2-brane, and $r_2$, the horizon radius.
The following relation is derived
$$-g_{00}
= -1 + \frac{16\pi G_{11}N_2T_\text{M2}}{9\Omega_7}r^{-6}.
$$
I dont understand how to get it.
The book explain
“ignore the directions along the brane and the result is ... |
I ask myself if the demand of local gauge invariance - say $U(1)$ invariance in free Dirac theory -$$L_D=\bar{\Psi}(i\gamma^\mu\partial_\mu-m)\Psi$$
is enough to define the full Maxwell-Dirac-Lagrangian UNIQUELY? I read that adding the Maxwell term $-\frac{1}{4}F_{\mu\nu}F^{\mu\nu} $ demands for other requirements like... |
Looking at various AdS/CFT correspondences, we find that some (n-1) dimensional field theories on the boundary of $AdS_n$ with $N=\frac{8}{n-3}$ supersymmetries are equivalent to M-Theory in $AdS_n \times S_{11-n}$.
(e.g. for $n=7$ we get 6D $N=(2,0)$ superconformal CFT.)
Setting $n=11$, seems to suggest that there is ... |
I am sorry if this question isn't clear, I couldn't think of a better way to phrase it. I am a Physics student trying to solve the angular component of the wave function for a particle in a central potential. I am sure that most if not all of you are familiar with the problem. Here is what I get for the polar wave func... |
The formula for air resistance is $$F_{air}=\frac{1}{2}\rho cAv^2 $$
where $\rho$ is the density of the air, $c$ is the drag coefficient, $A$ is the cross sectional area of the object and $v$ is the speed of the object.
We see that air resistance is independent of mass. So two indentically formed objects (such as a bow... |
Solving the particle in a box problem is fairly straight-forward for both, the finite and infinite potential well. While it is well known that the solutions to the infinite potential well must be orthogonal, it is not so obvious whether that should be the case for a potential well with finite height.
I tried to find r... |
Laplace transform is really interesting. Speaking about Fourier transform, there are many real world applications like we use in removal of noise and Laplace transform is again the extension of Fourier transform. Can anyone clearly explain the real world applications which mainly rely on Laplace transform and how it co... |
Every substance has an entropy, entropy is defined as the randomness in a system. There's also a term called molecular vibration which tells the periodic vibration of molecules and gives them a frequency. I've always thought heat of a substance is a property which defines the amount of random movement of the molecules ... |
Let's say we have a material $AB$. Is it possible to detect atomic clusters of A atoms experimentally?
The size of clusters in question: 2 atoms (nearest neighbour (nn) pairs), 3 atoms (nn triangles), 4 atoms (nn tetrahedrons).
|
I am trying to make sense of the following Wikipedia page. Do you know what the charge state $Z$ is? Do you know if there is a table or list somewhere which lists these parameters but in SI units instead of Gaussian units?
|
I'm trying to follow this paper in Section 3.1, but I'm having trouble with a comment they make in the final paragraph of that section.
First, we start with a pure state:
$$|\psi\rangle = \sum_i^m \sum_j^n a_{ij} |i\rangle |j\rangle.$$
Then, they consider the complex numbers $a_{ij}$ being uniformly distributed on a hy... |
Consider the following relations
$$H_0|\psi_a\rangle = E_a|\psi_a\rangle$$
$$H_0|\psi_b\rangle = E_b|\psi_b\rangle$$
I am struggling then to understand why the following identity holds (its probably straight forward but I just can not see it.) Note that r represents the position operator.
$$ \langle \psi_b| rH_0 - H... |
Suppose you have a superconducting wire with a constant current below the critical current and a resulting magnetic field below the critical magnetic field. If you were to wind the superconducting wire into a solenoid, the magnetic field would increase even though you haven’t added current. If you were to add enough wi... |
How should we interpret Boltzmann's distribution when the set $\{ E_1, E_2, \cdots, E_k \}$ (in increasing order) of energy levels is a finite set? In that case, the expected energy cannot exceed $E_k$, and in any case the infinite temperature distribution would be uniform over the $k$ microstates, and have expected e... |
I need to show that the recoil electron energy is:
$$ \varepsilon = mc^2 + \frac{(2\alpha \cos^2\phi)h\nu}{(1+\alpha)^2 - \alpha^2\cos
^2 \phi}$$
Where $\alpha = h \nu_0/mc^2$ and $\phi$ is the electron's momentum angle with relation to the incident photon. I've tried using the relation of $\theta$ and $\phi$ in the c... |
Recently, a meteroid bounced off the Earth's atmosphere. IIRC vehicles such as the returning Apollo craft also had the risk of bouncing unless they came in at a precise angle.
How is this possible?
Air in a sealed piston can act as a spring, but the real atmosphere is closed off. How is energy being returned to the mis... |
How do experimentalists at the LHC differentiate between jets produced by quarks and those produced by gluons. I know that for b quarks there is a b-tagging method, but what do they do for the others in order to separate them from gluon induced jets?
|
Why does the airflow at the leading edge of the wing curve toward the trailing edge of the wing?
Is it because the leading edge of the wing generates high pressure? High pressure pushes the air from the front edge to the trailing edge? We all know that air flow cannot change without a pressure difference.
|
In chapter 28 of Landau-Lifshitz Classical Mechanics textbook they try to explain how to get the motion of a particle with the Lagrangian:
$L=\frac{1}{2}m\dot{x}^{2}-\frac{1}{2}m w_{0}^{2}x^{2}-\frac{1}{3}m\alpha x^{3}-\frac{1}{4}m\beta x^{4}$
by using successive approximations for solve the motion equation:
$\ddot{x}+... |
What is pressure gradient? What is the unit of pressure gradient? Is pressure gradient only used in fluid mechanics? Are differential pressure and pressure gradient the same thing?
|
So assume a pressure-driven, incompressible, and steady flow in $x$-direction between 2 inf. fixed surfaces.
Why should the partial derivative $\frac{\partial P}{\partial x}$ in the Navier-Stokes Eqn. be constant?
My understanding is that:
not 0, since it's driving the flow
constant, so there is no acceleration (stead... |
I often see and hear people claiming that "the gravitational force is much weaker than the electromagnetic force".
Usually, they justify it by comparing the universal gravity constant to Coulomb's constant. But obviously, such comparison is meaningless, as they differ in dimensions.
I'll make myself clear: of course yo... |
The thin lens equation shows that when there is an object further than the focal point, there is a real image formed on the other side of the lens, and this principle is used for cameras, eyes, etc.
However, when I take a converging lens(that I got from some mobile VR headset), and hold it between me and an object, bot... |
While studying the quantum mechanics of $N$ identical particles, I stumbled upon formulas for generalizing the spatial wavefunction for bosons:
$$\psi(x_1,...,x_N)=\frac{1}{\sqrt{N!\prod_\alpha N_\alpha!}}\sum_p \psi_1(x_1)...\psi_N(x_N)$$
and for fermions, using the Slater Determinant:
$$
\psi(x_1,...,x_N)=\frac{1}{\s... |
Lets say you have a closed circuit connected to a battery made of copper wire. Lets say that at one point of the copper wire there is plastic. The electrons can't flow through the insulator and back into the wire. What force is allowing the repulsion of these electrons from entering the insulator? If there is no force ... |
I know how to normalize Legendre polynomials, but I have a sphere with 0 to pi/3 boundaries where the potential is $V$, otherwise zero. For normalization it is -1 to 1, what changes with different boundaries?
Is there a trick to find the coefficients $A$ and $B$ under different boundaries?
|
I'm trying to find the resonant frequency of glass panes and how the resonant frequency is affected by the thickness of the glass pane. I set up the glass pane with the ends of the glass pane fixed. (I want to pass a first harmonic wave through the glass)
I was thinking that I could tap the glass and hear the frequency... |
I'm currently reading a book about Quantum Physics. I was wandering what kind of effects do we see in every day life which can be explained by the equations of quantum dynamics?
I'm trying to connect between the equations and effect I'm familiar with (e.g. application of Quantum Physics in technologies such as MRI)
Tha... |
Show that If we add λΙ in H, where I is the identical operator and $λ\in\mathbb{R}$, it won't affect any measurement.
|
I am attempting to solve the Hamilton-Jacobi Equation in the case of a simple harmonic oscillator, to recover the associated generating function and the generated canonical transformation.
Consider the Hamiltonian:
$$\mathcal H=\frac{1}{2}\omega^2(p^2+mx^2)$$
where $\omega^2=k/m$.
Applying the Hamilton-Jacobi Equation:... |
In Velenik's Statistical Mechanics of Lattice Systems, Exercise 6.22 claims that if $\pi =\{ \pi_\Lambda:\Lambda \Subset\mathbb{Z}^d\}$ is a translationally invariant specification with nonempty Gibbs state $\mathscr{G}(\pi)$ (probability measures compatible with $\pi_\Lambda$), then the set of translationally invarian... |
According to Newton's third law of motion every action and reaction have opposite direction and are equal in magnitude, so for example, if I apply force on a block then every time applied force should be equal to frictional force and the box shouldn't move, then why the block finally moves? why my force applied overcom... |
Griffiths example 3.8 says
An uncharged metal sphere of radius $R$ is placed in an otherwise uniform electric field $\mathbf{E}=E_{0} \hat{\mathbf{z}} .$ The field will push positive charge to the "northern" surface of the sphere, and-symmetrically -negative charge to the "southern" surface ...
What's the proof that ... |
The four equations of Maxwell tell us how electromagnetic fields evolve in time.
Suppose we wanted to describe bulk phenomena... say resistivity for instance, then could we derive them starting from Maxwell's equations?
In this previous stack that I had asked (here), in the comments of the answer by user 'Emmy', one of... |
I wonder if there is any physical meaning associated to the determinant of the stress energy tensor. Or do we know at least some context in which this quantity is meaningful?
|
Suppose that we have a hermitian operator. Let's take for example the Identical operator $I: I\Psi=\Psi$. What does the operator $e^{I}$ do? does it result in $e^{\Psi}$ or something else? What happens if we replace it with the momentum operator $p$?
|
I would like to compare natural vs artificial (human) emissions in the radio spectrum (f < 1 THz).
The goal is to bring some scientific facts in the debate for deployment of 5G.
It's easy to find info for the spectrum around visible light :
I am looking for something similar for radio waves, and ideally some measures ... |
I understand how the field lines enter and leave the gaussian surface. But my concern is that the field isn't constant everywhere on the gaussian surface, i.e, there exactly doesn't exist an $- E\cdot da$ corresponding to every $E\cdot da$. I understand the idea of how the enlargement of the area compensates for the re... |
For the case of an ideal transformer, I understand that the voltages are proportional to the turns ratio.
$\frac{V_1}{V_2}=\frac{N_1}{N_2}$
since I assumed the transformer to be ideal:
$V_1I_1=V_2I_2$
so it follows that
$\frac{V_1}{V_2}=\frac{N_1}{N_2}=\frac{I_2}{I_1}$ -------(1)
So, from this equation it seems that th... |
I am having trouble understanding the effect of internal resistance on voltage. I have a circuit which is a real voltage source modelled as an ideal voltage source with EMF of Vs in series with an internal resistance of resistance Rs, and this real voltage source is attached to a load (Rload) of negligible resistance.
... |
Let's consider the modes of the em field for an empty rectangular cavity.
In the electric field expression the physical meaning of $\nu=\omega/2\pi$ is clear, it is the time frequency of the wave.
On the other hand, $\lambda=2\pi/k$ doesn't have a clear physical meaning. For my textbook (principle of laser by Orazio Sv... |
Some pieces of literature derives Joule thompson coefficent using enthalpy $H$ and others derive it using internal energy $U$ ... so which one is the right one? If they are both equivalent, then how do you prove their equivalence?
Edit: Ok, I realized there are actually two different JT coefficents called the JT coeffi... |
Free neutrons (outside the nucleus) are known to be highly unstable with a mean lifetime of around 14 minutes and 40 seconds. Inside the neutron, which is composed of 1 up quark and 2 down quarks, a down quark changes to an up quark by releasing a $W^-$ boson, and thus creating a proton.
$$d\rightarrow u+W^-$$
$$udd\ri... |
The so-called Ultimate Question is the question whose answer is a Theory-of-Everything. The trouble is that as far as I can tell theoretical physics are not certain what the question is they're trying to solve.
In quantum mechanics and quantum field theory, which has a separate notion of time, it seems like everything ... |
During non-uniform circular motion, the direction of net acceleration is not in the direction of the centripetal acceleration, then why does a particle still move in a circular path, please explain.
|
According to Doppler's effect
$$f'=\frac{v+v_0}{v-v_s}f$$
where $f'$ is the observed frequency, $f$ is the actual frequency, $v$ is the velocity of sound waves, $v_0$ is the velocity of the observer and $v_s$ is the velocity of the source.
Let us assume that I am at rest and I am observing a plane which is travelling a... |
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