2
votes
0answers
22 views

Ratio of Stagnation to Normal Flow Properties in Incompressible Flows

I know in compressible flows the ratio of stagnation to normal flow variables is a function of the Mach number and usually the specific heat ratio. Does this ratio mean anything for incompressible ...
0
votes
0answers
3 views

how to count such a huge number of oscillation in atomic clock

can someone help me out please?/ actually a second is defined as time taken for 9,192,631,770 oscillations of ceasium hyperfine levels...but its not exactly that the electron moves up and down between ...
0
votes
0answers
6 views

What is r-r' in spherical polar coordinate and cylinderical coordinate?

I am into solving Vector equations in Physics like Electric field and Magnetic field. $$E=\frac{1}{4\pi\varepsilon_0} \int\frac{\rho(r')\hat{\mathcal{R}}}{\mathcal{R}^2}d\tau'$$ ...
2
votes
1answer
43 views

Does changing a closed surface in the manner outlined contradict Gauss' Law?

As I understand it, Gauss' Law states that the electric flux on any arbitrary closed surface is equivalent to the sum of all charges enclosed within the surface times a constant. Mathematically, this ...
27
votes
5answers
3k views

Does a charged particle accelerating in a gravitational field radiate?

A charged particle undergoing an acceleration radiates photons. Let's consider a charge in a freely falling frame of reference. In such a frame, the local gravitational field is necessarily zero, ...
0
votes
2answers
490 views

Determining flexural modulus by performing 3 point bending test using hollow cylindrical tube

I would like to decide the flexural modulus of the material of plastic tube by performing 3 point bending test according to the ASTM D 790 procedure. In ASTM D 790, the form of the specimen is ...
0
votes
0answers
10 views

Resistance of a washer with square cross sectional area

Consider a resistor in the shape of a washer with resistivity $\rho$. It has a square cross sectional area $A$ and inner radius $a$ and outer radius $2a$. Find the resistance across the two wires like ...
0
votes
1answer
37 views

Can the question of a gravitationally accelerated charge radiation be tested experimentally?

I know that the question of radiation from a gravitationally accelerated charge has been discussed extensively at Does a charged particle accelerating in a gravitational field radiate?. Yet the ...
1
vote
1answer
52 views

Electric flux of a charged rod through a uniform disc

), I have an assignment regarding electric flux. The question I was given has the following sketch: The first question was about the force on the rod from the disc at the Z axis. I reached the ...
-2
votes
0answers
23 views

Pendulum acceleration vector [on hold]

I'll make this quick, I want the acceleration vector for a pendulum WITHOUT using angle acceleration and angle velocity, just using the tension and gravity forces.
-4
votes
1answer
33 views

Why can´t we call the energy released after the annihilation of a particle and its antiparticle `pure` energy? [on hold]

As a particle and its antiparticle annihilate each other a huge amount of energy is released, and no mass is left. This energy always comes in the form of force mediating particles (photons, gluons). ...
0
votes
0answers
52 views

QFT Weinberg scattering thoery

I have a question about beginning of chapter 3 (scattering) of QFT.vol.1 by Weinberg I think (am I wrong?) $\Psi_\alpha$ means a collection of particles each with a definite $p^\mu$ specially $p^0$ ...
0
votes
1answer
54 views

Derivation of Einstein's relation in Drift Diffusion model for Semiconductors

I'm currently reading Semiconductor Devices: Basic Principles by Jasprit Singh. In this book he gives a derivation of the Einstein relation for the Drift Diffusion model of semiconductors, supposing ...
5
votes
3answers
632 views

Rocket launch from a mountain

If we were to build a high speed rail up the side of a mountain like in some Science Fiction movies, what is the velocity needed at the point of leaving the mountain excluding angular momentum from ...
0
votes
1answer
20 views

How thin lens model work when there are two images with different distances from the lens?

I am trying to understand how thin lens camera work. From what I understand of thins lens model, the image is formed on image plane that obey the equation $$\frac1S_1 + \frac1S_2 = \frac1f$$ So ...
0
votes
0answers
9 views

Energy required to accelerate from different reference frames

So I've recently been studying relativity a lot trying to understand it and I feel like I grasp most things conceptually but I have one issue I've been trying to understand for the last couple days ...
0
votes
1answer
14 views

Flame composition types

Can anyone define the atomic structure of a carbon fuelled flame. I have studied variations of flame patterns but this type seems to stand out.
0
votes
0answers
13 views

Higgs mechanism in quantum GLSM

My question is regarding the following Gauged Linear Sigma Model (GLSM) in two dimensions. $$\tag{1} S=\int d^2x\Big(-D_{\mu}\overline{\phi} D^{\mu}\phi +\frac{D^2}{2e'^2} +D(|\phi|^2-r)\Big).$$ ...
1
vote
2answers
341 views

Which power equation to use: $P = I^2 * R$ or $P = V^2 / R$?

Given are ideal max voltage $V = 200\;\mathrm{V}$ and max current $I = 5\;\mathrm{A}$. Therefore: ideal resistance is $$R = \frac VI = \frac{200 \;\mathrm{V}}{5\;\mathrm{A}} = 40 ...
3
votes
1answer
427 views

Can we use radiation pressure to push/levitate a human?

I want to know, at least in theory, are there any safe em wavelength that could affect human body as net force and do no harm? To put it bluntly I want to know is it possible for levitate a human on ...
-1
votes
0answers
13 views

At which points Normal reaction acts on a moving object is more , if possible give an image for this , A,B,C,E . Thanks For Answering [on hold]

At which points Normal reaction acting on this moving object is more. We know that friction of a rolling body depends on the Normal Reaction Force. Situation 2 is the latter of situation 1 .I just ...
-2
votes
0answers
15 views

Condensed matter physics theorem?

I would like to summarize theorems in theoretical and experimental condensed matter physics. such as, say, Mermin-wagner theorem or LSM theorem .. etc. Plesase tell me the names of theorems what you ...
0
votes
1answer
18 views

When and how does magnetism pass through bodies?

I've seen a video by Walter Lewin in which the magnetic pull between two wires is unaffected when an aluminum plate is situated between them. Can you explain what materials let magnetism pass through ...
8
votes
2answers
783 views

Orbits around the Photon sphere of a black hole (Schwarzschild coordinates)

This is a follow-up question to the answer given at What is the exact gravitational force between two masses including relativistic effects?. Unfortunately the author hasn't been online for a few ...
3
votes
2answers
257 views

The ADM Energy of Gravitational Waves?

I have been looking for books about this question for several days. However, almost all books use Landau–Lifshitz pseudotensor to calculate the energy of Gravitational Waves.And they said the result ...
0
votes
4answers
236 views

Transformers and DC voltage

Ok, if I have a transformer with 100 coils of the primary and 200 coils on the secondary and I connect a 9 volt battery to the primary, how many volts should I expect from the secondary coil? I know ...
7
votes
1answer
383 views

Momentum Space Renormalization of $\phi ^6 $ Model

I'm trying to find the RG flow to lowest order in $\epsilon = 3 -d $ for the energy functional: $$ f=\frac{1}{2} \phi ^2 +u \phi ^6 +\frac{c}{2} (\nabla \phi ) ^2 $$ where $\ d$ is the dimension ...
2
votes
1answer
30 views

Does 'real' photon electromagnetically interact with matter?

Consider the standard description of Compton scattering - radiation is constituted of stream of photons (these are supposed to 'real' as contrasted to 'virutal' photons of the QED). One of these ...
0
votes
1answer
11 views

Which experiments of harmonic generation at low frequency are preceeding Franken SHG?

In "The principles of Nonlinear Optics" by Shen, he says that that generation of harmonics at low frequencies were long known before Franken did SHG in optical range. "Franken's idea was simple. ...
0
votes
1answer
17 views

Why , under constant light intensity and constant frequency, do electrons emitted from a metal surface travel at different speeds?

I was playing around with this PheT simulation: https://phet.colorado.edu/en/simulation/photoelectric Under a certain threshold wavelength and an intensity at 20%, the electrons were being emitted ...
14
votes
1answer
187 views

Why are LIGO's beam tubes so wide?

Gravitational wave detectors and particle accelerators have at least one thing in common -- they require long vacuum tubes through which a narrow beam is fired (a laser in the gravitational wave case, ...
4
votes
1answer
294 views

Equations of motion of displacement field

We have an action: $$S[\boldsymbol{u}] = \frac{1}{2} \int dt \int d^3x \left\{ \mu (\frac{\partial u_{i}}{\partial t})^{2} - \nu (u_{ii})^{2} - \rho(u_{ij})^{2}\right\} $$ Where $u_{ij} = ...
0
votes
0answers
11 views

what is the reaction force of electromagnetic force created on a conductor in a magnetic field?

If a force is created on a conductor carrying a current in a magnetic field, what does the reaction of this force act on?
1
vote
1answer
13 views

Systematic+Random Uncertainty for velocity measurement

I have a question regarding systematic and random uncertainties. I have to measure the mean value of a velocity measurement in flow field at a point. I've recorded say 1000 samples in time, which I ...
6
votes
2answers
158 views

How do we explain the existence of liquids, from a mathematical or computational perspective? [on hold]

This post asks why matter exists in three phases. Most of its answers explain the existence of liquids with some variant of the following: liquids happen when thermodynamic conditions, temperature ...
42
votes
5answers
6k views

Why is Helium so hard to liquify?

By the end of the 19th century all gasses had been liquefied apart from helium (He). What is it about helium that makes it so hard to liquefy compared to the other gases? And why does it need to be ...
1
vote
1answer
26 views

What is a good book to self-teach optics?

I'm interested in camera lenses and how things like barrel distortion and lens flare happens, but know that one cannot just start there. I'm a math major and I've worked out of Strauss PDE book so I ...
1
vote
1answer
137 views

Reaction in Particle Physics

I'm currently checking some reactions if they are allowed. One of them is $$\nu_\mu p\to\mu^-\Delta^{++}$$ Since this is a weak interaction I've checked the Baryon and Lepton number, Spin and the ...
-3
votes
0answers
27 views

Is using nonlinear crystals considered nonlinear optics according to you?

Ok let me rephrase would you consider interaction of nonlinear crystals with light that does not have enough intensity to induce nonlinear polarization ?
1
vote
1answer
206 views

Can two bodies of different mass attached at ends of string passed over a frictionless pulley produce equal tension on both sides?

In my textbook there is given a case that to calculate acceleration and tension produced in string when string is attached at it's ends with two bodies of masses such that $m1>m2$ and the tension ...
-4
votes
3answers
36 views

Can we bring the distribution of the landing places of falling leaves from a tree bring in connection with a Lorenz attractor? [on hold]

I have already asked a few weeks ago if the motion of a falling leave is chaotic. Wich it is. But if we consider the collection of the trajectories of all the falling leaves, a pattern emerges on the ...
3
votes
3answers
279 views

Sliding ruler on table top

I've got a standard foot-long flat plastic ruler (about an inch wide) and a desk with a smooth formica-like surface. When idly passing time reading on the computer, I will pick up one side of the ...
-2
votes
1answer
29 views

Which one of these energy formulas is correct?

Which one of the following formulas is correct? What do they mean/represent? How are they used? $E=mc^2$ $E^2=m^2c^4+p^2c^2$ $E=\frac{mc^2}{\sqrt{1-\frac{v^2}{c^2}}}$
1
vote
0answers
10 views

Optical bandpass filter at focal point of lens

Optical bandpass filters are designed for a particular angle of incidence (AOI), e.g. see Fig 4 here. However that is for the ray picture of light. Imagine I have a thin bandpass filter positioned ...
2
votes
1answer
42 views

How can you find the impact necessary to change the direction of Earth's spin?

If an object the mass of the moon was to hit earth's surface at an angle that would be in the opposite direction of earth's spin, how can you find how much momentum the object needs to cause earth to ...
-3
votes
0answers
30 views

A Take on Dark Energy [on hold]

Extreme over-simplification alert (the full proof is hundreds of pages long and it’s quite unfinished as of yet). Okay, I have a simple (enough) explanation of what dark energy is, but I am not sure ...
4
votes
2answers
759 views

Degeneracy in one dimension

I'm reading this wikipedia article and I'm trying to understand the proof under "Degeneracy in One Dimension". Here's what it says: Considering a one-dimensional quantum system in a potential ...
2
votes
3answers
243 views

Entropy change in an irreversible process between 2 equilibrium state

Calculating entropy change in an irreversible process between 2 states requires computing the change in entropy for any reversible process between the 2 same states, but why? If someone could provide ...
1
vote
1answer
89 views

Deriving Pauli Matrices

How does one derive using, say, the operator formula for reflections $$ R(r) = (I - 2nn^*)(r),$$ the reflection representation of a vector $$ R(r) = R(x\hat{i} + y\hat{j} + z\hat{k}) = xR(\hat{i}) ...
0
votes
0answers
9 views

How is zonal flow defined and computed?

The transition to turbulence in pipe flow was recently observed to be in the same universality class as directed percolation. This was done by reinterpreting the turbulence and laminar flow in terms ...

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