3
votes
5answers
4k views

Can a black hole collapse in itself?

As we know that the black hole is a lump of highly dense matter, and that's the reason for it's so strong gravitational force. Bat let us assume that it has sucked up a huge amount of mass and it's ...
5
votes
2answers
36 views

Does the solar wind correspond to a net electrical current?

The solar wind is a stream of ions emitted from the sun. Are there more positive than negative charges released? That is, is there any imbalance in the charge emitted from the sun in the solar wind?
0
votes
1answer
21 views

What causes a charged particle to follow circular motion in a magnetic field? [duplicate]

I would like to know why particles follow a circular path in a magnetic field, what path they trace and how this path is measured and controlled?
1
vote
1answer
25 views

Solution of Burgers' equation in preshock region

According to Hamilton's & Blackstock's Nonlinear acoustics (Section 4.5.4) the solution of Burgers' equation of the form: $$ \frac{\partial P}{\partial \sigma} - \frac{1}{\Gamma}\frac{\partial^2 ...
2
votes
1answer
71 views

Is a nearby parallel universe still in use as an explanation for dark matter?

Is the theory which explains dark matter as the effect of a nearby parallel universe still used as an explanation for dark matter, or does this theory already lie on the pile of forgotten theories?
6
votes
1answer
38 views

Mathematical definition of wavefront in case of non harmonic waves

What is the general mathematical definition of wavefront? Wavefront is the surface where, at fixed time, the phase is constant But for non-harmonic waves we cannot talk about phase as the ...
-1
votes
0answers
19 views

Determine the shear in dislocation [on hold]

I don't know how to solve this kind of problem: Given a crystal and its volume V. This Crystal is subjected to a shear stress making a slip plane (h k l ) in a slip direction [h k l]. Given also the ...
0
votes
2answers
18 views

The direction of frictional force in circular turning

Why does the frictional force in case of circular motion point towards the center even though the motion is tangential to the radius?
1
vote
2answers
42 views

Can air be considered incompressible as long flow velocities are less than 100 m/s (Ma = 0.3)?

Multiple sources state that steady air flow (in open systems) can be considered incompressible at velocities less than 100 m/s (Ma = 0.3). Example: Deborah A. Kaminski, Michael K. Jensen, ...
0
votes
0answers
18 views

What is the name of basis states of bulk k.p Hamiltonian?

A k.p Hamiltonian for a bulk material can be represented by 8x8 matrix in basis of $|S\uparrow\rangle$, $|S\downarrow\rangle$, $|X\uparrow\rangle$, $|Y\uparrow\rangle$, $|Z\uparrow\rangle$, ...
12
votes
1answer
182 views

Explaining causal completion axiom in Haag-Kastler axioms?

There are several variants of the Haag-Kastler axioms for algebraic quantum field theory. Usually one associates an algebra $\mathcal{A}(O)$ to each open region $O$ of spacetime. An often-suggested ...
41
votes
5answers
5k 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 ...
-3
votes
1answer
13 views

Relationship between refractive index and concentration [on hold]

what does the gradient of the graph of refractive index against solution concentration mean
0
votes
1answer
13 views

What is the vapour pressure of carbon at room temperature?

The vapour pressure of carbon at 3642°C is one atmosphere (this is the sublimation temperature given in Wikipedia). At lower temperatures, the vapour pressure will be less, but of course it will ...
0
votes
1answer
49 views

How long will it take to collect enough energy to eject an electron [on hold]

A light source with intensity $1\ \mathrm{Wm^{-2}}$ shines on a piece of potassium. The binding energy of the electrons in potassium is $1.8\ \mathrm{eV}$. The “Bohr radius” of an atom is ...
2
votes
0answers
32 views

Barycenter correction for inner planets in solar system?

I want to run simulations of the solar system, and I've read in some papers that to speed up the simulations it is useful to use the barycenter correction of the inner planets (from Mercury to Mars), ...
-2
votes
0answers
24 views

Working out total electrostatic force [on hold]

To work out this question, would you find the electrostatic forces between z and y and z and x using the formula F=kq1q2/d^2, and just add them?
13
votes
3answers
2k views

Hypercharge for $U(1)$ in $SU(2)\times U(1)$ model

I understand that the fundamental representation of $U(1)$ amounts to a multiplication by a phase factor, e.g. EM. I thought that when it is extended to higher dimensional representations, it would ...
5
votes
1answer
172 views

Will the CMB rest frame always coincide with co-moving coordinates?

I understand that the CMB rest frame for a typical FLRW universe should coincide with co-moving coordinates, but under what conditions won't the two coincide? For example if the universe had some net ...
7
votes
2answers
206 views

Is entropy absolute (as in absolute temperature)?

Following this question on the Entropy at the Big Bang where I asked: Since Entropy always increases (in general); its expected that the entropy at the beginning of the universe should be the ...
0
votes
1answer
25 views

Can vernier scale ratio be less than 1?

I came across a question (See Image) that states about two vernier scales The first vernier scale is the top-most figure in the image: It has 10 vernier scale division equal to 9 main scale division ...
1
vote
0answers
34 views

Finding the exponent of $\lambda$ in Wien's displacement law

I am reading this paper on a short history of the $T^4$ radiation law. In particular, on page 5, By assuming that the wavelength of radiation emitted by a molecule was a function only of its ...
0
votes
2answers
335 views

How does back-emf oppose the input-current?

A circuit, has current $A$ flowing at a certain $V$. When there is a change in magnetic-flux, based on Faraday's law of induction & Lenz's law, we know that there is change in Potential ...
1
vote
0answers
30 views

Diffusion of carbon monoxide in air

I have been reading about carbon monoxide online. It is lighter than air; Yet, in the case of fire, most online sources claim it spreads evenly throughout a room. Why is this the case? How is it ...
-1
votes
1answer
18 views

Are stainless steel more radiation absorption than carbon steel?

Are stainless steel more radiation absorption than carbon steel? and if it is so why?
1
vote
2answers
11k views

Dimensonal analysis of damping constant?

What are the units of the damping constant from the following equation by dimensional analysis? $$\zeta = \frac{c}{2\sqrt{mk}}$$ I'm assuming the units have to be s^-1, as the damping constant is ...
1
vote
0answers
10 views

Different charges of plates of parallel plate capacitor

Suppose the plates of a parallel plate capacitor have charges +2Q and -Q initially. Then if they are connected with a battery of emf V what will be the charge distribution on the plates of capacitor? ...
4
votes
1answer
48 views

Hubble time and age of the universe

I'm having trouble with the following derivation of the 'age of the universe': http://imgur.com/gRvLWX8 The parts I'm struggling to conceptualize is what a 'universe expanding' means, and also why ...
5
votes
1answer
10k views

Intensity of unpolarized light through polarizer

When unpolarized light is polarized with two polarizers, the intensity becomes $I=I_ocos^2(θ)$ (Malus's law). But when unpolarized light is polarized with only one polarizer, the intensity is reduced ...
41
votes
1answer
3k views

Classical and quantum anomalies

I have read about anomalies in different contexts and ways. I would like to read an explanation that unified all these statements or points of view: Anomalies are due to the fact that quantum field ...
24
votes
4answers
1k views

When can a global symmetry be gauged?

Take a classical field theory described by a local Lagrangian depending on a set of fields and their derivatives. Suppose that the action possesses some global symmetry. What conditions have to be ...
1
vote
1answer
47 views

Relativistic transformation of electrical current

If, in frame $S$, we have an electrically neutral wire with some current $I$, modelled as positive charges moving in $x$ direction and negative charges moving in $-x$ direction, then how would one ...
17
votes
1answer
610 views

Vibrational anharmonic coupling and noise-induced spontaneous symmetry breaking in a hexagonal finite mechanical lattice

Happy holidays, everyone! The following is part question, part visual gallery, and part classical mechanics problem. Inspired by snow over the weekend I began simulating the vibrations of the ...
2
votes
1answer
22 views

Coupling constant for an object in a photon gas

I want to model a photon gas as a bath of harmonic oscillators, and examine the effects of this bath on a system which is also a harmonic oscillator. The trouble I'm having is in relating the ...
0
votes
0answers
12 views

units of measurement in Bloch equations

I am trying to understand the Bloch equations for understanding MRI and the equation describes the change of magnetization during NMR excitation and relaxation as: $$ \frac{dM}{dT} = \gamma M \times ...
1
vote
0answers
26 views

BTZ Black holes

I computed the two point function for two scalar fields in BTZ black hole that is defined as a local $AdS_3$ space time with discrete identification, as defined in many papers. Referring to this ...
0
votes
1answer
112 views

Simultaneous measurement for quantum entanglement

In the simple example that we measure the spin of two entangled particles, we measure one to have spin up so we know the other has spin down. If we could (theoretically) measure both particles at the ...
45
votes
4answers
3k views

Why do some location on Earth have only one tidal maximum per day instead of two?

Most places in the ocean have two high tides and two low tides per "day" (~25 hours). But I remember reading that some locations only have one of each per day. This answer has some great explanations ...
4
votes
2answers
234 views

Electric Field inside a diode

When a voltage is applied to a diode (Forward or Reversed bias) the depletion zone is changed due to charges change in this region. My question is in both case (Forward or Reversed bias), how the ...
3
votes
0answers
61 views

Integration by parts with Dirac Delta function

I am having some hard time trying to understand the following "heuristic" integral, involving integration by parts with the Dirac's Delta. We start with the following relation $$ f(x) = ...
2
votes
1answer
32 views

Measuring the growth of the Hubble sphere

I have a question which I believe will greatly help my understanding of the Hubble sphere and what it means physically. Say we have a flat ($k=0$) Universe with no dark energy ($\Lambda=0$) during ...
0
votes
3answers
232 views

How is Capacitance affected by a seperation distance and with or without a battery?

The questions specifically says this : A parallel-plate capacitor initially has capacitance $C$. The distance between the plates is then doubled, with a $9.0V$ battery connected. The battery is then ...
0
votes
1answer
27 views

What is the physics with examples behind the boundary conditions for heat, wave and Laplace equations?

Mainly there are three types of boundary conditions, TYPE I, TYPE II, TYPE III. TYPE I is also known as Dirichlet conditions, i.e, $u(0,t)=f(t),\,\,\mbox{and}\,\,u(L,t)=g(t)$ TYPE II is also known ...
1
vote
1answer
48 views

Power generation with a long, horizontal pipe, using atmospheric pressure differences

Straight to the point. If I float a pipe starting from a point in the ocean that has the atmospheric pressure of 101 kPa (Call it Point A) all the way to another geographic position on the ocean with ...
0
votes
2answers
110 views

How the standard units for length force and time are defined in US Customary Units as standard units are defined in SI?

I'm much confused about US customary units so I want to ask a lot more questions under single question.First how standard units ,in US customary Units,of force time and length are defined as second or ...
0
votes
0answers
8 views

Solving Bloch equation for MRI

I am trying to write a numerical solver for Bloch equation to track the magnetisation of a spin during the excitation and relaxation processes. The general Bloch equations can be written as: $$ ...
4
votes
1answer
37 views

Which way the water evaporate faster?

-Hello everyone, Yesterday I was preparing some tomato sauce and, in order to remove some water from the sauce, I put it in a pot on the burner and waited until it started to evaporate. When I sow a ...
1
vote
1answer
48 views

What is the difference between a tensor, vector, and a matrix? [duplicate]

I'm currently going through notes on a physics course and I'm having trouble understanding the difference between a tensor, a vector, and a matrix. I know that a vector is a kind of tensor and that a ...
1
vote
1answer
54 views

Proportional acceleration due to changing density of the Earth

My question has to to do with a recent video minutephysics posted about the time it takes for a person to fall through the earth, found here https://www.youtube.com/watch?v=urQCmMiHKQk At around ...
-4
votes
2answers
68 views

Why did big bang occur? [on hold]

Why did big bang occur? Why did it expand from singularity? By why I mean to ask what disturbed it's equilibrium homogeneous state, that it suddenly inflated? Like if there was some sudden ...

15 30 50 per page