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Propagation Of Error Calculation Of Incompressible Continuity Equation

Hello I am having trouble deriving the correct equation for error in vertical velocity from the incompressible continuity equation. We are trying to estimate vertical velocity ($w$) from the ...
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2 answers
110 views

Let $Q(t,\vec x)$ solve $\partial_t^2 Q = \nabla^2Q$. Why $\partial_t^2Q = 2 (\partial_r + r^{-1})\partial_{t-r}Q$?

On page 5 of Bondi et. al. (1962) (https://doi.org/10.1098/rspa.1962.0161), a suitable method for solving the gravitational wave equation is demonstrated for the case of the scalar wave equation. ...
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30 views

Expanding the ratio between infinitesimal time elements [closed]

Given the expression $$ \sqrt{\frac{1 + \frac{2}{c^{2}}\phi(r_{S}) - \left(\frac{v_{(obs)}}{c}\right)^{2}}{1 + \frac{2}{c^{2}}\phi(r_{E})}}, $$ where $\phi(r_{S}), \ \phi(r_{E}), \ v_{(obs)}$ and $c$ ...
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1 answer
29 views

Non-additivity of higher order terms in the intermolecular potential

The intermolecular potential energy can be written as $$u(r_{1},...,r_{N})=\sum_{i<j}^{N} u_{2} (r_{i},r_{j}) + \sum_{i<j<k}^{N} u_{3} (r_{i},r_{j},r_{k})+...$$ where the nuclear coordinates ...
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1 vote
0 answers
56 views

Ruling out dependence of y and z coordinates in Lorentz transformation

Let us assume that motion is in the $x$ direction, axes of both coordinate systems are aligned and their origins meet at $t=t'=0$. The most general relation between $x$ and $x'$ then becomes (ruling ...
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1 answer
31 views

How to "calculate" correctly the liquid column height in not "simple" capacities?

As I was told on a youtube lesson, to calculate the hydrostatic pressure on the bottom of a capacity, that's on the picture below, I need to use the h1 height(see that formula on the picture). And it ...
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0 answers
68 views

Can a school student publish research paper? [closed]

I am a high school student. I want to publish a research paper now which I have written . Will I face any problem regarding this. Will there be any problem regarding my educational qualification . Is ...
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2 answers
31 views

Does a pressure jump form as a result of surface tension even for a flat interface?

My question is fairly straightforward, is a curved interface the only way a surface tension-induced pressure jump can form over that interface, or is it also possible to occur over a flat surface? ...
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-1 votes
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49 views

Maxwell equation in material media assuming periodic fields

In article https://aip.scitation.org/doi/10.1063/1.440709 authors use the following equation for treatment of electromagnetic waves in dielectric material with inhomogenous electric permitivity: $$(\...
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40 views

What is the gauge symmetry of wave equations in curved spacetime?

The lagrangian of electroweak interaction is invariant under $SU(2)\times U(1)$ gauge transformations, QCD lagrangian is invariant under $SU(3)$ gauge transformations. There're lagrangians of ...
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28 views

Would isotopes of hydrogen separate in liquid phase?

According to https://www.aqua-calc.com/calculate/volume-to-weight the difference in density of deuterium/hydrogen in liquid state is 70miligrams/cm^3 vs 169miligrams/cm^3. Would this be a sufficient ...
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1 answer
40 views

Query about average velocity of gas molecule

When we can say that gas molecule average velocity is 0 and in which case it is not possible?
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2 votes
1 answer
65 views

A doubt about Kirchhoff's scalar diffraction theory

Scalar diffraction theory assumes a scalar wave equation of the form $$\frac{1}{c^2}\frac{\partial^2u}{\partial t^2}=\nabla^2u$$ where $u(\vec{r},t)$ is a scalar field called the optical disturbance. ...
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0 votes
1 answer
24 views

Pipe Heat Exchanger problem [closed]

I use a heat exchanger to convert vinyl from different phases, such as converting vinyl from liquid to gas; or from steam to gas, can we use hot water instead of steam to convert to gas? If possible, ...
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0 answers
11 views

How to design a coil for neodymium magnet speaker [closed]

For reasons I won't elaborate in depths here here I need to design a speaker-like oscilating element, that is ring shaped so it fits onto a suction cup so it can be easily attached to any flat surface ...
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0 votes
1 answer
21 views

UV-absorption capability of air

I am looking for an absorption chart for UV light with a wavelength of around 250 nm in air (ambient, no specific preparation). How much of a beam of this light would be absorbed per meter of path ...
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3 votes
0 answers
36 views

Decomposition of the Photon Propagator into $K$ and $G$ propagators

I am reading a paper by B. Sahoo and A. Sen, called "Classical and Quantum Results on Logarithmic Terms in the Soft Theorem in Four Dimensions". To determine the logarithmically divergent ...
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0 answers
35 views

What is the spin degree of freedom? [closed]

In one paper I was reading, a factor of two was added because of the spin degree of freedom, what is exactly meant by the spin degree of freedom?
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2 answers
50 views

Self-Inductance of a coil: What is the logical reason to not just write $\Phi = L * I$ but we also add the factor $N$ to the left side?

What is the reason to not just write $\Phi = L\cdot I$ but we also add the factor $N$ to the left side? ($N\cdot\Phi = L\cdot I$) $\Phi$ is in Webers here, and is the induced magnetic flux. $L$ is the ...
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0 votes
1 answer
39 views

Does the force that need to be applied to pull the weight out of a well by string is more at the start?

One way to estimate depth of the well is attaching a weight to a string then throwing it into the well until it touch a hard surface then pulling the string out of the well and evaluate its length. ...
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  • 267
-1 votes
0 answers
18 views

How would sound waves travel in microgravity, if the sound source was placed in a container filled with water in space? [closed]

I'm in a summer space research school project with 3 other students, we are designing space probes. The best design, amongst competitors all over the country, will work with space engineers on a real ...
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0 answers
16 views

Negative moment of inertia on incline [duplicate]

This would be the expression for the moment of inertia on an incline $$I=\frac{MR^2(g\sin-a)}{a}$$ however this would suggest that there is a limit to acceleration for certain angles of the incline ...
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2 votes
0 answers
62 views

Strong gravitational force induced by static electromagnetic fields?

This 2004 preprint by B V Ivanov claims that static electromagnetic fields can create strong gravitational fields. He claims a capacitor charged to 100 kV loses 1% of its weight and a capacitor ...
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-1 votes
0 answers
41 views

Born's Rule for a continuous specturm of eigenvalues

I learned that given that the eigenvalue equation is $$ \widehat{A}\left|u_{n}^{i}\right\rangle=\lambda_{n}\left|u_{n}^{i}\right\rangle $$ where $ i \in\{1,2, \ldots, g_n\} $, and that the state $ |\...
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1 vote
0 answers
11 views

Is there any physical advantage in placing the sample between the recombined beam and the detector in Fourier Transform spectrometry?

Usually, in all the implementations of FT spectroscopy the sample is always placed between the recombined beam and the detector like in this figure from Wikipedia: Theoretically, the interferometer ...
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1 vote
0 answers
20 views

What is the maximum possible averge power of the geomagnetic electric generator?

Earth's magnetic field strength varies from 25 to 65 μT on the surface. Therefore, magnetic energy is approximately $V\frac{1}{2} \frac{B^2}{\mu\mu_0} \approx 10^{\left (17,5\cdots 18,5 \right )} \...
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0 votes
0 answers
26 views

If in principle all processes are $TPC$ symmetric then what causes the direction of time?

Let's assume all processes are TPC symmetric. Be it the breaking of an egg (just reverse all momenta of all particles involved), the evolution or collapse of the wavefunction (a big if but let's ...
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  • 152
1 vote
1 answer
22 views
+50

Relative angle of magnetic fields in DC Motor

I'm building my own generator. What is the ideal angle between the magnetic field of the stator in relation to the induced magnetic field of the rotor? Is there a formula to calculate it? For some ...
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  • 153
3 votes
1 answer
160 views

Are the sources in QFT just particles?

I'm reading A. Zee's Quantum Field Theory in a Nutshell, where he introduces QFT using path integral formulation. One thing that I'm not sure I got correctly is this: Zee adds a source term to the ...
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  • 900
2 votes
1 answer
50 views

The proof of the Wigner-Eckart theorem for irreducible tensor operators

I am reading through Wu-Ki Tung's Group Theory in Physics and I met a problem when going through the part of the Wigner-Eckart theorem for irreducible tensor operators. In the 4.3 part of the book, ...
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2 votes
0 answers
41 views

Massive and massless modes in the Klein-Gordon equation

I am studying the massive Klein-Gordon equation in 3+1 dimensions with a given scalar source. The equation I am looking at is $$ (\Box +m^2)\phi(x)=J(x) \ , $$ and am interested in the following ...
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0 votes
1 answer
74 views

Tong QFT Problem set 2, question 6: Normal ordering of angular momentum operator

I've been studying Tong's QFT notes and am trying to do problem sheet 2, question 6. here. We are asked to take the classical angular momentum of the field, $\begin{align} Q_i &= \epsilon_{ijk}\...
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  • 21
0 votes
3 answers
37 views

Can't figure out my mistake in solving the problem of spring hanged from the ceiling and a weight attached at its end [closed]

A spring with the length $50cm$ and $k=400\frac Nm$ is hanged from the ceiling. Then we attach a weight with the mass $m$ at the end of the spring and while the spring has its normal length, we ...
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  • 267
1 vote
0 answers
32 views

On the Integral Representation of Greens Functions

In Birrell & Davies book "QFT in Curved Spacetime" the authors discuss in chapter 2.7 that all Greens Functions (which are the vacuum expectation values of products of fields) can be ...
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0 votes
0 answers
10 views

Resonant Frequency in Mutually Inductive RLC Circuits [closed]

After attempting this, I got equations for both currents, but I don't know how to get the resonant frequencies. Everywhere I look says its when the inductive and reactive capacitance are equal, but I ...
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0 votes
2 answers
17 views

What is the definition of the Rayleigh-Jeans tail?

I've read some papers using the term "Rayleigh-Jeans tail" but cannot find a general definition. I would infer from context that it refers to the blackbody emission spectrum in the range of ...
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  • 434
2 votes
1 answer
86 views

What's wrong with my argument about entanglement entropy in QFT being time-independent?

Let's say we need to compute the entanglement entropy (EE) of a subsystem $A$ ($A=[0,L]$, $L>0$) in a 2D CFT. The density matrix of the total system (i.e., the real axis) is given by $$ \rho(t)=\...
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0 votes
0 answers
20 views

Dark Matter Axion in Toroidal Coil [closed]

I got this question for some homework, but I don't know where to start. I've tried using the 4th equation, but I can't get anywhere. Any suggestions on where to start would be appreciated, thanks.
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8 votes
6 answers
1k views

Can the wavelength of the standing wave be different from the wavelength of the sound it emits?

I have a question about standing waves on strings. I'll try to explain the best I can, I searched and researched the whole day yesterday but I am confused still: Every frequency has a single, and ...
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4 votes
1 answer
78 views

Do irreversible thermodynamic processes CONSTITUTE time or do they MOVE IN time? [closed]

Time can be associated with irreversibility. A broken egg can't reassemble. Most, if not all, processes are irreversible and this is associated with time going in one direction. Ŕemarkably, living ...
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  • 152
0 votes
0 answers
12 views

How to calculate total sum of orientation changes in 6 DOF data from a Motion tracker?

I'm using data from a motion tracker that give provides 6 coordinates for every frame ( with frame rate of 240Hz) Position: x, y, z Orientation: azimuth(yaw), elevation(pitch), roll I can calculate ...
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1 vote
1 answer
34 views

Comparison of 2 fans [closed]

I have 2 20" box fans. The first fan draws .65 Amp and claims 1780 CFM. The second fan draws .45 Amp and claims 2300 CFM. The fans are new, and the electric motors are of similar design, so I ...
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  • 13
0 votes
0 answers
40 views

Survival of only $\hat{y}$ term in calculation of magnetic field of toroid [closed]

I'am reading the Griffith, Introduction to Electrodynamics, p.238, Example 5.10 and I stuck at understanding some statement: I can't understand the underlined statement completely. Q.1) How the $\hat{...
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3 votes
1 answer
50 views

Wave nature of light [duplicate]

In a light source (like filament of bulb) there are various atoms and as such the things are deemed to be randomised. So there must be a phase difference between each of the wavetrains emitted by the ...
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-2 votes
1 answer
66 views

Special relativity and proper time, is crash course physics wrong? [closed]

I was watching the Crash Course Physics video on special relativity: Special Relativity: Crash Course Physics #42 It basically starts off from the ubiquitous light clock experiment to demonstrate ...
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0 votes
0 answers
24 views

Showing that flux fluctuation is $q^2 P_n(q)/2\pi$

In the context of spectral analysis of a sufficiently small section of the sky, 1 states that the flux fluctuation is given by $q^2 P_n(q)/2\pi$ on the angular scale of wavelength $2\pi/q$, where $P_n(...
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  • 91
9 votes
4 answers
2k views

Addition of gravitational fields in general relativity

According to Newtonian gravity, when dealing with multiple sources of gravity, the net gravitational field equals the sum of the individual gravitational fields of each source. Does the same hold for ...
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  • 515
0 votes
0 answers
14 views

Frequency dependent Purcell effect for a broadband emitter

How do I model the following system? I have an NV-center in diamond with a broad fluorescence spectrum, centered at roughly 700 nm with a FWHM of 100 nm. (The NV-center is a defect in diamond, it can ...
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  • 13
5 votes
2 answers
856 views

Why does a stream of falling water get narrower at the bottom? [duplicate]

At first glance, I thought that the flux of the velocity field, $\mathbf u$, should be constant. The velocity of the water increases due to gravity, hence the imaginary area the velocity field is ...
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0 votes
1 answer
39 views

Matrix representation for Gupta-Bleuler creation/annihilation operators

I am wondering what would be the closest analogue of the matrix representation for the creation and annihilation operators arising in Gupta-Bleuler formalism, which are defined by $$ [a,a^\dagger] = -...
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