# All Questions

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### What is the current density of a circular current?

Lets consider a wire loop in the $xy$-plane of radius $R$ which carries a current $I$. I want to find the current density $\vec{j}(x)$ of that configuration expressed with delta functions. Intuitively,...
5 views

### The cavity method of Ising model in infinity dimension and dynamical mean field

In the article "Dynamical mean-field theory of strongly correlated fermion systems and the limit of infinite dimensions" chapter III.A, when discussing the cavity method of Ising model, the ...
28 views

### What would be the value of $c$ where $c$ is the speed of light?

From the equation of $E=mc^2$, where $E$ is the energy, $m$ is the mass and $c$ is the speed of light, so from that we can get $c=\sqrt{Em}$, again from the equation of $\lambda=v/f$, where $\lambda$ ...
6 views

### How would the vacuum look like if no mass/energy is present in it?

The observable universe is thought to inflate faster and faster towards infinity. The energy will be diluted to zero in the far future. The influence of attractive gravity is getting smaller and ...
• 1,637
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### How does the scale of a cataclysm determine if we can look beyond it?

The textbook I am referring to (Physics for Scientists and Engineers ($9e$), page $1 469$, section $46.11$), has the following paragraph regading the Big Bang: ... This theory of cosmology states ...
• 2,721
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### If gravity was lower but air density was the same, how would evaporation be affected?

I'm confused about the relationship between air density, air pressure and gravity. Does water evaporate faster under low air pressure simply due to the air density being lower? If the air pressure was ...
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1 vote
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### Is it possible that there is a third class of fermions?

There exist six types of quarks, and six types of leptons, both divided in three generations. Could there be some other new class of exactly six particles, similar to these, but with properties such ...
• 11
22 views

### In a black hole, why the speed of a photon matter to it to escape the black hole?

I read that a black hole doesn't attract light but bend it. By that, I understood that the photon is going forward but the space-time is so bent on itself that the photon goes forward infinitely into ...
6 views

### Is there any role of permittivity of medium in finding electrostatic force between two charges in that medium in CGS system?

like from coulombs law,we know electrostatic force,F=(1/4πε)(Qq/r^2).....in SI System But in CGS this whole term 1/4πε got replaced by 1.,i just want to know like in SI ,for different mediums, we use ...
12 views

### Benefit of Hydrogen Electrolysis

I was considering building a simple solar hydrogen generator for fun and it led me to the question Does the hydrogen produced have more potential energy than the electricity used to get it? Obvious ...
10 views

### Question regarding gravity and quantum entanglement

We know that the Earth is revolving in an elliptical orbit around the Sun. However, if the Sun suddenly disappeared, the information would then travel to the earth, at the speed of light, and the ...
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### Is this right that the fate of space expansion depends on matter density inside the universe?

Is it right think that a right amount of matter density inside the universe could eventually stop the expansion of the universe or the expansion of space is something intrinsic only to space so the ...
• 1,917
1 vote
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### What is the modern status on the Skyrmion theory of baryons?

It was noticed in the 1960s that chiral perturbation theory, describing the goldstone-bosons (pions) of the breaking $SU(N_f)_L \times SU(N_f)_R \to SU(N_f)_V$ of the chiral symmetry, has solitonic ...
• 5,704
22 views

### Wouldn't Millers planet be ripped to shreds by extreme tidal forces?

If you can survive lava-like temperatures there is another issue for the well-being of Miller's planet from Interstellar. Time passes on the planet 61000 times more slowly than for an observer far ...
• 5,175
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### Can an object move with a constant velocity without balanced forces?

Can an object move with a constant velocity without the balanced forces? As an object which is balanced with the frictional force continues moving at a constant velocity, acquired till then. How does ...
33 views

### Are scalar and vector potentials solutions to Maxwell's equations? [closed]

Are scalar and vector potentials $\phi = 0$, $\vec{A} = A_0 \cos (kx-\omega t) \hat{e}_z$ solutions to Maxwell's equations? Do these potentials correspond to the Lorentz and Coulomb calibration?
30 views

### What is the best criterion to discern between classical and quantum physics? [duplicate]

I ask this question here knowing there are similar questions on this site, but not having found a satisfactory answer for myself below those. Or at least, one in which a comparison between different ...
1 vote
16 views

### What does Specific Heat capacity of a material depend upon?

I have read in many places that specific heat capacity is an property of the material but I haven't really understood what it depends upon, as in what factors affect that specific heat, I have thought ...
1 vote
30 views

### How does a sliding object stop moving by the effect of kinetic friction, if kinetic friction is constant and Fk can't be greater than Fapp on its own

The kinetic friction is constant. So if say, I apply a force of 20N on an object and the kinetic friction is 13N, then how does the object stop moving after some seconds. I believe that kinetic ...
23 views

### Comprehension question regarding thermodynamics

This question got me stuck, I got the 1st one but am not getting the 2nd and 3rd ones. !(https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSn_EqhSH-...
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### Basics of photoelectric effect

DISCLAIMER: I have not yet fully entered into the vast field of quantum mechanics and and was reading about the photoelectric effect as a part of chemistry, however I feel, the topic of structure of ...
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29 views

### Moving body is collided with a spring system.Why there is a difference in maximum compressed distance for different observers?

Suppose a body of mass m moving with velocity collides with a spring system.The event is being observed by two observers, one at rest and one moving with a velocity v opposite direction to that of the ...
12 views

### Finding Rout for both diagrams

A designer needs to evaluate the performance of a regulated cascode current mirror as shown in Figure 1 comparative to the conventional cascode current mirror topology illustrated in Figure 2. Perform ...
23 views

### Plate with positive potential and Gouy-Chapman model

I am thinking about the following mental experiment. Imagine I have an infinite flat plate at $z=0$ with electrostatic potential $\phi_0$, i.e., $\phi(z=0)=\phi_0$. Now I embedded this plate within an ...
• 117
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### How to get local density field of a compressible solid Neo-Hookean material undergoing large deformation?

My understanding of a compressible material in the context of non-linear elasticity in continuum mechanics is that the volume of the body can change due to the applied forces. Due to the law of ...
1 vote
20 views

### Second partial derivatives of thermodynamics potentials at the critical point

I'm trying to understand the physics of phase transitions, specially at the critical point, but I find myself stuck. For an hydrostatic system, I studied the stability conditions, that lead to (in the ...
15 views

### How the pressure will change inside a pressure chamber if there is a hole in the pressure chamber?

Let's say I have a pressurized tank with a fixed volume(V), I have 400psi of pressure inside it. Now a hole/orifice of 2mm diameter is made in the tank. Obviously, the pressure will now start leaking ...
32 views

### Special relativity book which describes concepts using linear algebra notions

It seems so every idea of special relativity can be formulated quite nicely in Linear algebra notions such as the inner product matrix and change of basis matrices. However, I can't find a single book ...
1 vote
14 views

### Regarding calculation the moments of a random variable whose probability distribution obeys the Fokker Planck equation

I was going through Van Kampen's Stochastic Processes in Physics and Chemistry, and I was trying to solve the exercises from Chapter 8 about the Fokker Planck equation (just in case context could help ...
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### Break angular velocity into components given angles in relation to the $xz$, $yz$, $xy$ planes

I am working with a Smooth Particle Hydrodynamics package called DualSphysics. This package is able to simulate ridge floating bodies. Below is the structure that defines a floating body: ...
• 1
1 vote
33 views

### The relation between full Green's function and S-matrix

I'm learning Green's function in condensed matter. The full Green's function is defined as $$G(k_2,t_2;k_1,t_1) = <\Omega |T a_{k_1}(t_1)a_{k_2}^{\dagger}(t_2) |\Omega>$$ The $\Omega$ is the ...
53 views

### Can X-rays travel quicker than visible light in a medium?

I have seen while reading a few books that the refractive index depends on lambda as follows by the Cauchy equation. $${\displaystyle \eta(\lambda )=A+{\frac {B}{\lambda ^{2}}}}$$ From this, the book ...
14 views

### Time statistics of a single photon source

Say I have a single-photon source, and a 100% efficient detector. Can one say what the time-series of clicks of this detector would look like? Does it depend on the frequency distribution of the ...
• 1,552
35 views

### Matter-antimatter annihilation and CMBR [duplicate]

Does this intensity of microwave background radiation correspond to the huge amount of gamma photons that could be released during the theoretical annihilation of matter and antimatter at the time of ...
• 1,917
28 views

### Probability of observing harmonic oscillator at a particular position

Consider a classical harmonic oscillator whose Hamiltonian is $$H=\frac{p^2}{2m} +\frac{1}{2}mw^2x^2$$ where $w$ is the oscillating frequency. I wish to find the probability of observing the harmonic ...
• 3,813
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### Electrostatics Question For JEE [closed]

A Conducting Sphere Has Charge Q uniformly distributed over its surface.Let a Gaussian Surface of same radius but passing through the centre of the same sphere. The total flux linked with the Gaussian ...
1 vote
13 views

### How do I approximate an angular acceleration vector from a history of orientations?

A rigid body is simulated to move in six degrees of freedom. At every past timestep, I know its displacement vectors $x^{GLOB}$ in the global coordinate frame, as well as 3x3 matrices $R$ that ...
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33 views

### Do tsunamis accelerate on land?

Before they saw the footage, Fritz and Synolakis couldn't understand why so many people had taken photos posing with the wave behind them, out on the open ocean. For some victims, those pictures would ...
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1 vote
47 views

### Question about constraint in lagrangian

We know that the lagrangian can be written using constraints. Suppose I have constraint functions $$f_1=\cos(x) - (x+t)/R=0,\qquad f_2=\sin(x)-y/R=0 .$$ But I know that $1=\cos^2+\sin^2$, so do we use ...
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### Why the General Lomb-Scargle results are doubled?

I got a problem when computing the GLS on MATLAB for my master deegree thesis. I need to do a comparison between the PSD and amplitude spectrum of a signal computed with three different metods, the ...
1 vote
37 views

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### Does the electric field due to Faraday's law have zero divergence? [duplicate]

How do we know that the electric field that is produced due to Faraday's law of induction does have zero divergence since when proving Maxwell's equation of gauss law, where the divergence of electric ...
9 views

### How (if) is the metric of the quantum vacuum different from the metric of the classical vacuum?

The classical vacuum, with no matter or energy in it, has a flat metric. Meanwhile we know that the classical vacuum is a chimera. There are lots of things going on, eventhough its called virtual. ...
• 1,637
19 views

### Thermodynamics question about refrigeration [closed]

A laboratory refrigerator removes heat from its interior at 2°C and release it to the surroundings at 30°C. Solve the following questions in details, i.e. provide concise and meaningful procedure. a) ...
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### How to find the force exerted by continuous jet of water on a wall? [closed]

Suppose, the water is flowing at a speed of $2m/s$. The cross-sectional area of the opening is $0.03m$, and the water is hitting the wall at right angles. Assuming the water doesn't rebound, how will ...
1 vote
The total flux ($\Phi$ ) through an solenoidal inductor of length $l$ and $N$ turns is proportional to the current through the inductor and the inductance $L$ of the inductor according to \Phi =L \...