0
votes
0answers
3 views

Is entropy of all systems zero at absolute zero?

Is the entropy of every system zero at the absolute zero? Or is it taken to be zero at the absolute zero? Are there systems that doesn't reach zero entropy even till absolute zero?
-2
votes
0answers
9 views

Магнитный щуп сразу решит все проблемы

Сейчас стало возможным купить магнитный стержень из готовой номенклатуры или оформить заказ под свои размеры. Ассортимент представленных пробников, щупов и магнитных стержней обусловлен длительной ...
-5
votes
0answers
11 views

Барабан небольшой длины для измельчения крупного материала

Стальной барабан цилиндрической шаровой мельницы футерован внутри плитами из марганцовистой стали или базальта. Плиты заклинивают внутри барабана; они имеют разные размеры и образуют волнообразную ...
1
vote
0answers
11 views

Functional field integral in condensed matter field theory(Altland)

This is the action for the 1+1 dimensional interacting electron system; $S_{cl}[\theta , \phi]= \frac{1}{2\pi} \int dxd\tau \left(g^{-1}v(\partial_x \theta)^2 + gv(\partial_x \phi)^2 + ...
0
votes
1answer
4 views

If air was significantly compressed, and then the force compressing it suddenly disappeared (no container), what would happen?

Question: If air was significantly compressed, and then the force compressing it suddenly disappeared (no container), what would happen? Side Question: I'm imagining significantly compressed, but ...
0
votes
0answers
9 views

Solving the Poisson-Boltzmann Equation for a charged plane with positive and negative ions in solution

I am trying to solve the Poisson-Boltzmann equation for a positively charged plane with charge density $\sigma$ at $z = 0$. $$ \phi''(z)=-\frac{e}{\epsilon \epsilon_0} \big(z_+n_{+} e^{-\beta z_+ ...
1
vote
3answers
18 views

What is the relationship between the Schwarzschild radius and Black hole Singularity?

What is the relationship between the Schwarzschild radius and Black hole Singularity? Can the Planck length be the length of singularity? Or is the length of the Schwartzschild shorter than the ...
2
votes
2answers
16 views

Consider a horizontal surface with or without friction. Ideally, will a wheel rolling without slipping roll forever in both cases?

Suppose a wheel is rolling smoothly on a horizontal plane i.e., it is rolling without slipping. Now let's take the two cases of the horizontal plane: It has friction It is frictionless In the ...
1
vote
1answer
19 views

Understanding vectors in an example

I just read an example of vectors in my book which is confusing me. Three particles A,B and C are at the vertices of an equilateral trinagle ABC. Each of the particle moves with constant speed v. ...
-2
votes
0answers
12 views

Find the magnitude of the induced current I(t)

Use Lenz’s Law to figure the direction of the current. Is it positive or negative for small t according to the direction drawn in figure?
-2
votes
0answers
13 views

Calculate voltage at different times

Calculate the voltage across each resistor and capacitor in the circuit shown (1)before, (2)right after, and (3)long after the switch is closed.
0
votes
1answer
16 views

Gravity wave, Planck length and Schwarzschild radius

I have heard that Schwarzschild radius corresponds to the Planck length when the radius gain the Planck energy. Is the gravity wave length (amplitude) equal to the Planck length?
0
votes
0answers
20 views

Given the final position of projectile and initial magnitude of the velocity, how to solve for the initial angle?

Using the two equations of motion in the x and y directions, (starting at the origin) $x=v_0 \cos(\theta)t$ and $y=v_0\sin(\theta)t-gt^2/2$ How do I solve for theta? I've been told to use the trig ...
0
votes
1answer
27 views

Why there are no uuu and ddd baryons with spin 1/2?

What is preventing $Δ^{++}$ and $Δ^-$ baryons from going to a lower-energy state with spin 1/2 similar to that of protons and neutrons? I don't think the Pauli exclusion principle can prevent it ...
0
votes
0answers
15 views

Acceleration in stationary spacetime

How would I show $ a^\mu = u^\nu \bigtriangledown u^\nu = \bigtriangledown^\mu lnV. $ for an observer instantaneously 'at rest,' where $u^\mu = dx^\mu/d\tau$ and $V^2 = -\xi_\mu \xi^\mu$ ($\xi^\mu$ ...
0
votes
1answer
24 views

Calculating decibel gain and loss

I'm doing a mobile/wireless networking subject and the physics aspect is giving me some trouble. I'm mainly confused about the conversion of dB, dBm and dBW and how to calculate the gain/loss from an ...
3
votes
0answers
25 views

Linear field approximation to gravitation

I'm attempting to learn about the linear field approximation for gravity, and I found a few resources that are helpful, but I am having trouble understanding the gauge invariance. I am attempting to ...
1
vote
0answers
16 views

Does dark matter get drawn into black holes?

Would dark matter get drawn into a black hole? Also, could enough dark matter be concentrated to create a "dark black hole"?
6
votes
3answers
315 views

Does electricity flow on the surface of a wire or in the interior?

I was having a conversation with my father and father-in-law, both of whom are in electric related work, and we came to a point where none of us knew how to proceed. I was under the impression that ...
0
votes
0answers
8 views

Does bragg diffraction affect intensity of transmitted light?

Is it possible to measure the plane spacing in a crystal by measuring the angle at which transmitted light intensity dips?
2
votes
0answers
30 views

Modified gravity and dark energy

Is there a model of modified gravity that either was close to or have succeeded in modelling the problem of dark energy, and suffers from no instabilities and explains the observational data. Also has ...
0
votes
1answer
34 views

What happens to the acceleration of a body undergoing constant force?

Here's the problem I have, specifically relating to a rocket in deep space: A rocket burns fuel at a constant rate. Assuming its mass remains constant, what happens to its acceleration? I seem to get ...
1
vote
2answers
72 views

Would being underwater help survive a nuclear bomb?

If I jump in my pool, on the river near my house knowing that a nuclear bomb, or atomic or H-Bomb exploded around 10 km from my house, would I survive? The way I see it is that water will protect me ...
1
vote
0answers
27 views

Do generalized Pauli Operators generate SU(n)?

A commonly used generalization of Pauli Operators is the "clock" and "shift" operators summarized here: http://en.wikipedia.org/wiki/Generalizations_of_Pauli_matrices Pauli Operators are generators ...
1
vote
1answer
11 views

Relative perimittivity of conductor?

Why is the relative permittivity $\epsilon_r$ infinite for a conductor? Where does it come from mathematically and does it make physical sense?
2
votes
0answers
20 views

DC current in ideal conductor and skin effect?

I know that the skin depth derived for AC current goes as $$\delta \propto \sqrt{\frac{1}{\omega \sigma}}$$ where $\omega$ is the angular frequency of the field and $\sigma$ is the conductivty. Now: ...
4
votes
0answers
21 views

Does the LSZ reduction method prove gauge-independence in massless gauge theories?

I've been working my way through L. Baulieu's excellent paper [Perturbative gauge theories, Physics Reports, Volume 129, Issue 1, December 1985, Pages 1-74]. Towards the end, he goes on to prove that ...
2
votes
5answers
124 views

Is there no radioactive decay between nuclear fusion and solid material formation?

I'm aware my question might be considered a duplicate of this one: Radio-dating and the age of the earth I read that one and I looked everywhere and I still can't find my piece of mind. I would ...
2
votes
4answers
35 views

Doubt about states of matter

What does exactly means "Small molecules may appear as solid, liquid, and gaseous phases without losing their molecular integrity"?, I can't image how just a molecule can be a gas, liquid or solid. ...
0
votes
0answers
24 views

Ricci/Tensor Calculus and Matrix Calculus

What are the differences in the types of problems Ricci/Tensor Calculus and Matrix Calculus can solve? One formulation is generally used by the physics community and the other by statisticians and ...
0
votes
0answers
57 views

Is it really “time” that is dilating?

Consider the following variation of the twin paradox: A clock or a biological system ultimately is an electromagnetic system. First, let’s devise a new time measuring device. Imagine a tank of ...
0
votes
1answer
12 views

Transition between spin-up and spin-down states in magnetic resonance

What is the classification of the transition between spin‐up and spin‐down states in magnetic  resonance (such as NMR, ESR, MRI)?
3
votes
2answers
43 views

Associated Legendre Integer Giving Full Asimuthal Range and Physical Interpretation of $l(l+1)$

In separating the Laplacian in spherical coordinates, one arrives at the associated Legendre equation (ALE). Write the ALE as $$\frac{1}{\sin \theta} \frac{\partial }{\partial \theta}(\sin \theta ...
0
votes
0answers
37 views

Which one to choose for theoretical physics phd: SISSA or IMPRS? [on hold]

I am a non-EU student, did my MS in physics and want to work in theoretical physics for my PhD. My major areas of interest are in theoretical particle and astro-particle physics, quantum field theory ...
1
vote
1answer
39 views

Do I understand impedance correctly?

$$Let\quad \vec { Z } =R+Xj$$ If $X>0$,then the impedance is lagging (current lags behind voltage).If $X<0$, then the impedance is leading (current leads voltage or more accurately, voltage lags ...
0
votes
0answers
22 views

Realtivistic explanation of forces between two conducting wires

The formula for the force between two infinite conducting wires per unit of length, $F_l = \frac{\mu_0}{2\pi} \frac{I_1 I_2}{r}$, is quite well known. It was used for definition of ampere and was ...
5
votes
0answers
40 views

Why can't I use Bell's Theorom for faster than light communication?

I read this description of Bell's theorem. I understand he's restating it slightly, so there may be incorrect assumptions there, or I may have some. I think Bell's theorom should lead to FTL ...
-3
votes
0answers
17 views

Finding flux of magnetic field [on hold]

A square loop of side a carrying a current i is placed in x-y plane with abcissa of it's centre at 3a/2. Find flux of magnetic field for x<0. Ans. (μia/2π)ln2 Please provide the solution
0
votes
0answers
7 views

Inductor's energy

I have some knowledge about LC circuits, like I know Maxwell's equations, the differential equations of circuit oscillator and so on. I am armed with equations to solve physical problems involving ...
1
vote
0answers
21 views

In a universe that is expanding at a constant rate, do objects that are attracted to each other feel a force opposite to their attraction?

In this article, the authors make the claim (pg 44) that "Expansion by itself—that is, a coasting expansion neither accelerating nor decelerating—produces no force." I'm having a hard time convincing ...
0
votes
0answers
8 views

Can the motion of a cracking whip be described as the interference of two waves?

I was watching a whip crack in slow motion and I noticed that the motion of the whip could be described using two different circular descriptions. 1) the user circles the whip around over his head, ...
1
vote
2answers
34 views

wave-particle duality and entanglement

By fundamental definition of a entangled system we can say that if we know the quantum state of one subsystem then we can describe the state of another subsystem. A particle possess wave-particle ...
0
votes
1answer
28 views

Infinite potential well with barrier in the middle- symmetric

So I'm having problems with the double infinite potential well given by $$V(x)= \left\{\begin{array}{ll} \infty & -\infty < x < -a-b \\ 0 & -a-b< x < -a \\ V_0 & -a < x ...
0
votes
0answers
25 views

Was the mass of the universe the same when it first began as it is now? [duplicate]

I've heard that the big bang began in all places at once, but my physics teacher told my class that the universe was all once compressed into a single dense piece of matter. If my physics teacher is ...
0
votes
0answers
7 views

Finding the gate source voltage and the resistance of the drain capacitor in a MOSFET circuit [on hold]

I'm trying to catch up on a module I missed. Here I have a feedback-biased MOSFET circuit. For question 1 where it asked me to find the drain current when $V_{GS} = 5$. Which I calculated to be ...
1
vote
0answers
13 views

Conformal mapping for calculating magnetic reluctance

I work currently on the calculation of magnetic resistance for a air-gap of an electrical machine. For this I am using conformal transformations. I am doing this on a 2D slice. As the machine is ...
10
votes
3answers
292 views

What happens in a car crash?

Me and mom were in a car accident. We are ok, but I want to know how fast the car that hit us was going. We were stopped at a light. The car that hit us from behind was a big GMC SUV. Our car was a ...
2
votes
1answer
19 views

Energy conservation when capacitor charges in a zero resistance circuit

We know that when a capacitor charges from a source $E$, it stores energy of $E=\frac{1}{2}QV $. This is derived without taking into consideration any resistances present in the circuit. We also ...
3
votes
0answers
23 views

How does a plasma globe work?

I am trying to simulate a plasma globe using computer. But I do not know how to model the motion of its filaments. My first guess is to construct a potential field. And the filaments are the paths ...
0
votes
0answers
14 views

Interacting fermionic SPT phases in 2d with time-reversal symmetry

Interacting fermionic SPT phases in 1d and 3d with $\mathbb{Z}_2^T$ symmetry are classified by $\mathbb{Z}_8$ and $\mathbb{Z}_{16}$ respectively, as shown in the paper by Fidkowski and Kitaev ...

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