5
votes
2answers
192 views

Is there a general systematic approach how to calculate the individual terms in an operator product expansion?

Is there a general systematic procedure or approach to obtain the analytic functions $c_{ijk}$ as well as the corresponding operators $$A_i(z)$$ that appear in the operator product expansion (OPE) $$ ...
0
votes
2answers
495 views

Using the Normalization Condition with Wavefunction

I'm very confused with this problem and I was looking for some guidance. $$\psi(x) = Ae^{ikx}e^{-x^2/2a^2}$$ Use the normalization condition to find A. So I understand that you use the normalization ...
1
vote
0answers
67 views

Finding the force of an object? [closed]

Sorry if my initial question was seen as a "homework question" but I don't really know how to go about asking this type of question. I have a feeling I have to use Newtons law but there is no ...
5
votes
0answers
160 views

Hall conductivity from Kubo: Bulk or edge?

Using the Kubo formula, Thouless, Kohmoto, Nightingale, and den Nijs (TKNN, PRL 49 405-408 (1982)), proved that upon summing all the contributions of the filled states of an insulator, the Hall ...
2
votes
0answers
149 views

Boundary Condition for Perfect Conductor in Uniform Magnetic Field

When I was studying the perfect conductor scattering (Section 10.1) in Jackson's book, I was confused by the calculation for magnetic dipole induced by the incident wave. He simply said like "set the ...
0
votes
1answer
79 views

Current in AC circuit

The problem is to find the current on the capacitor. $I''$ should be correct, but I don't know how to construct the formula for $I'$. I managed to get the value for $I_c$ using Thevenin and Norton ...
1
vote
1answer
230 views

How to derive the expression for Bose-Einstein distribution variance?

Can anyone point me to a derivation of this expression? $n_s$ is the number of bosons in a state.
8
votes
2answers
337 views

Hexadecapole potential using point particles?

We can get monopole $1/r$, dipole $1/r^2$, quadrupole $1/r^3$ and octupole $1/r^4$ potential falloff by placing opposite point charges at the corners of a point, line, square and cube, respectively. ...
4
votes
2answers
136 views

Tensor fields on space-time

I'm reading landau electrodynamics . For the investigation of the dynamics of a charged particle in an electromagnetic field , the author introduces a four vector potential field on spacetime . The ...
8
votes
3answers
336 views

Where does the extra equation come from to determine the forces from an object on a table?

I have a question about basic statics but somehow I cannot manage to find the answer on my own (btw, this is not a homework. It's been so many years since school for me...). The problem is very ...
7
votes
0answers
339 views

Why do we identify symmetric 2nd rank tensors with spin-2 particles in string theory?

I am going through Tong's lecture notes on String Theory and came across the following irrep decomposition (Chap 2, p.43) of the bosonic string first excited states: $$\text{traceless symmetric} ...
1
vote
2answers
376 views

Path Integral Quantization

I was reading through my notes on the path integral quantization of bosonic string theory when a general question about path integral quantization arised to me. The widely used intuitive explanation ...
6
votes
2answers
161 views

Gauge fields and strings: Loop equations

I am trying to derive Eq. (7.25) (p. 117) of Polyakov's book: $$ \delta \Psi (C) = \int_{0}^{2\pi} {\rm P} \left(F_{\mu\nu}(x(s)) \exp \oint_C A_\mu dx^\mu \right)\dot{x}_\nu \delta x_\mu(x) \, {\rm ...
1
vote
2answers
464 views

Will a spinning object come to rest?

Will a sphere spinning on its own axis come to rest given enough time, provided no other forces act upon it? I know that if you have two spinning spheres in the depths of space and orbiting each ...
8
votes
3answers
3k views

What about negative Pressure?

Here is something I see : Let's say the ideal fluid(water here) of density $\rho$ is drawn from a source by a motor and thrown upwards with a velocity $v$. Now we take the power of motor be ...
15
votes
1answer
555 views

Discreteness of set of energy eigenvalues

Given some potential $V$, we have the eigenvalue problem $$ -\frac{\hbar^2}{2m}\Delta \psi + V\psi = E\psi $$ with the boundary condition $$ \lim_{|x|\rightarrow \infty} \psi(x) = 0 $$ If we ...
1
vote
2answers
873 views

Getting started with Landau Physics course [closed]

I want to learn Physics in my own time. I am an electrical engineer, working in the same field and am tremendously interested in Physics. I have heard a lot about the 10 book series of Landau ...
1
vote
0answers
492 views

How the value of permitivity of free space is determined?

when electric charges are placed on the medium then force of interaction between them decreases. We say this factor permitivity of the medium. The force of interaction between the charges is max if ...
0
votes
1answer
427 views

From Fermi-Dirac to Maxwell-Boltzmann statistics

I have a little question I can't seem to find the answer to. It is as follows: When does Fermi-Dirac statistics reduce to Maxwell-Boltzmann statistics?
0
votes
1answer
97 views

Magnitude of a photon?

I encountered the following sentence in my textbook, which I don't quite understand, and after an unfruitful google search, I still can't figure out what they mean by magnitude in this context: ...
1
vote
1answer
86 views

Entropy of Black Hole

What is the relation between the entropy of rotating and non rotating Black hole? Which one's entropy is greater?
1
vote
1answer
248 views

Inclined plane question [closed]

An object, mass $m$ is placed on an incline, angle $\theta$. System is at equilibrium. coefficients of static and kinetic frictions are $\mu_s$ and $\mu_k$ respectively. Then: 1) What is the Total ...
1
vote
1answer
74 views

Can a link between photons that don't exist at the same time provide communication with the past?

They have published something about a link between photons that don't exist at the same time. Does this means that it is possible to build a device that will receive messages from itself but these ...
11
votes
2answers
965 views

Is the meander ratio of a river $= \pi$?

To get from point $A$ to $B$, a river will take a path that is $\pi$ times longer than as the crow flies (I think this result is from Einstein). What is the proof of this, and how well does it hold ...
1
vote
0answers
72 views

Salisbury Screens and Energy Conservation

From Wikipedia on how a Salisbury Screen works: 1. When the radar wave strikes the front surface of the dielectric, it is split into two waves. 2. One wave is reflected from the glossy ...
6
votes
1answer
134 views

Causal structure of the inflationary multiverse

In the multiverse as it is described by eternal inflation, it is not clear to me what is its causal structure and in particular if the bubble-universes are causally connected. We start from a ...
-1
votes
1answer
67 views

Calculate energy from an reaction [closed]

I'm trying to calculate the released energy from a reaction. The radioactive substance polonium decays according to this formula: $$^{210}_{84}\mbox{Po} \rightarrow \mbox{X}+^4_{2}\mbox{He} $$ At ...
1
vote
1answer
133 views

What does the wavevector $\textbf{k}$ mean?

In Ashcroft, Mermin Solid State Physics, Eq. 17.43 is $$ \epsilon(\textbf{k}) = \frac{\hbar^2 k^2}{2m} - e\phi(\textbf{r}) $$ where $\textbf{k}$ is the wavevector and all other symbols have their ...
1
vote
2answers
123 views

Points in Spacetime

Assume there are two points in spacetime $a=(t,x,y,z)$ and $a'=(t',x',y',z')$. Let's say that the first one is in the origin of spacetime i.e. $a=(0,0,0,0)$. The point $a'$ has two possibilities ...
3
votes
1answer
131 views

Non-isolated universe and arrow of space

Could you please help me to understand two statements in physics: 1) Universe by definition is an isolated system. But universe expands, space pours into universe, space (vacuum) has zero-point ...
0
votes
2answers
4k views

What happens when non-equal voltages are put in parallel? [duplicate]

If two batteries, say 2 volts and 5 volts, are connected in parallel, are there any problems? The higher voltage will then want to flow out, but also towards the lower 2 volt battery end, right?
1
vote
2answers
265 views

Work on Ferromagnetic Object Due to Solenoid

I've been going through some equations and such trying to determine the work done by a solenoid on a ferromagnetic object. I have the following: Magnetic field due to solenoid: $\vec{B} = ...
1
vote
0answers
110 views

Is there any place you can safely skydive without a parachute?

While trying to explain to someone how a kitten walked away from a fall from a skyscraper I got to wondering if there's any place a human could do that and I find myself out of my depth. The only ...
4
votes
3answers
201 views

Why does sound move faster in solids?

I know that the molecules are closer together in solids, and I know thicker springs also respond carry waves faster than thinner springs, but for some reasons I can't understand why. The molecules ...
3
votes
1answer
173 views

Phase Space dimension of Lorenz Strange Attractor

It is often discussed in 3 spatial dimensions and the need for third dimension to prevent self intersection is mentioned. But shouldn't the phase space of the Lorenz system be 6 dimensional, i.e., the ...
2
votes
0answers
102 views

How long would it take for a container in vacuum to leak half of its air? [closed]

Let's say I know the size of the container, size of the hole the air leaks through, pressure the air is under and temperature of the air if that helps anything. Is it possible to calculate this only ...
1
vote
0answers
152 views

How to find outflow pressure/force of air through a pipe

I have been trying to find the correct method for determining the outflow force resulting from a certain amount of air being forced into a pipe of a certain dimension. Essentially i'm trying to ...
-1
votes
1answer
211 views

Electric dipole moment, which charge is the $q$ for?

Electric dipole moment says $p = qd$. Which charge does the $q$ equal to?
4
votes
2answers
324 views

How do you come up with a POVM?

This is a made-up example, just to understand a concept. If changing the probability values aids your explanation, that's fine by me. Say you have a physical quantity $E$ that can take values 1, 2, 3 ...
4
votes
4answers
7k views

Terminal velocity of all falling objects is same?

Ideally 2 objects of different mass and weight will hit the floor at same time because they face same gravitational pull and accelerate. Will the terminal velocity of both objects be same also? and ...
1
vote
0answers
55 views

Physics (measurement) [closed]

In october,1707 four British warships ran aground because of error in position,sparking the effort to produce a marine clock that would be accurate to locate a position with in 30 miles after sailing ...
12
votes
2answers
575 views

Does an elliptical orbit of a satellite maintain its orientation as the Earth revolves?

Imagine a satellite in an elliptical orbit around Earth. As the earth travels around the sun, does the elliptical orbit of the satellite swing around Earth, as pictured in A, or does it maintain a ...
3
votes
1answer
916 views

Can a linear momentum generate angular momentum at collision?

I'm trying to get the facts straight here. Suppose I'm throwing a ball with no angular momentum. It collides with the ground and Newton's third law tells us that a force opposite to the gravity will ...
3
votes
1answer
308 views

Diameter of the universe [duplicate]

Should the diameter of our universe always be more than its age in light years? As if the distance between any two points in the universe is equal to 13.5 billion light years then the light from the ...
-1
votes
1answer
65 views

What is the maximum speed of a change? [duplicate]

Is there any limit on the speed of changing something? For example a particle is transformed to some other particle; This takes some time or is absolutely instant? If every change takes some time, ...
2
votes
1answer
143 views

What is the distance traveled

the red dots represent a side view of path traveled, F is downward force and the tool used here is a pen placing parallel to the coin I have newly started to study mechanical physics. based on study, ...
0
votes
3answers
169 views

Violation of Newton's 3rd law

I'm just expressing my guess. Let two particles A and B experiences forces $F_1$ and -$F_2$ between them and let guess also there are two observer, one is stationary and other is moving with ...
6
votes
4answers
272 views

Physical interpretation of changing variables $S(T,V)$ to $S(T,p)$

I'm confused in this situation. In an example of this book (Example 16.5. Thermal Physics, by Blundell) they ask to prove that $$C_P - C_V = VT\frac{\alpha^2}{\beta_T}\tag{1}$$ but using the fact ...
6
votes
1answer
137 views

Why does this screwdriver roll in a curved trajectory?

I am trying my level best to give this screwdriver a horizontal push only, but it is going in a circular path. I thought of uneven friction due to non-uniform normal reaction...what do you think? I ...
0
votes
0answers
50 views

Color of sky scattering by sky dust [duplicate]

Why does we see sky like blue in maximum time? We know violet has less wavelength, so we should see sky like violet. My assumption is that, violet is not primary color and not sufficient in the ...

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