# All Questions

29 views

### Can a flow of current be produced in a wire if its is bombarded with Electromagnetic waves?

If you have a conducting wire and you bombarded it with EM waves, is there a frequency (lower then the threshold frequency to liberate the electrons) that would induce a current within the wire. I ...
9 views

### Assumptions that led to Wigner surmise of nuclear level spacings

In 1957, Wigner surmised (guessed) that the probability density of the spacing between adjacent energy levels of complex nuclei is given by $$P(s) = \frac{\pi}{2}s e^{\frac{-\pi s^2}{4}}$$ This is ...
28 views

### The question about an observer and an observed environment [on hold]

Imagine that Bob is observing everything that is not him (environment). The experiment: the environment changes somewhere far away from Bob. The conclusion: The change propagates in the ...
12 views

### the total deviation produced by slab when Ray comes out [on hold]

Q) A ray of light travelling in air is incident at grazing incidence on a slab with refractive index,$n(y)=[ky^{3/2}+1]^{1/2}$ where $k= 1m^{-3/2}$ and follows path as shown in figure. What is the ...
27 views

### Homework question on the Poynting vector

I need to show what the Poynting vector becomes when i insert the definition of A through creation and annihilation operators, what i get is the expected answer plus a term containing two creation ...
21 views

### How many times does baryogenesis happen during the history of the universe?

Does the baryogenesis happen both in GUT epoch and electroweak Epoch during the history of the universe? If yes, are there any differences during this two times?
48 views

### What is the physical implication of a homomorphism between SU(2) and SO(3)?

It can be shown that there exists a homomorphism between $SU(2)$ and $SO(3)$. What is the physical implication of a homomorphism actually? I know that in physics $SU(2)$ acts on a space of spin 1/2 ...
35 views

### Metal density increase [on hold]

Can you increase the density of a material (metal) by surface treatment? For example commercial copper. If we take the ordinary OF copper (99.95%), I would expect not to have the tabulated 8.92/8.96 ...
21 views

### Background and references for topological string theory

Where would one start to learn about topological string theory knowing no string theory? What are the general prerequisites and what kind of background in QFT is needed? Is a conventional book like ...
25 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?
25 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 ...
68 views

### How do light waves get their size?

An atom or (small) molecule has the size of about 100pm. Elektromagnetic waves range from about 0.1nm up to 1 km. The most common way waves (like light) are caused by 'jumping' electrons to another ...
4k views

### Supergun Launching of Satellites

I should say first that I don't believe this is a feasible launch method, otherwise NASA and other space agencies would be using it by now. It's based on this BBC news story Saddam Hussein's Supergun ...
20 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?
14 views

### Relationship between refractive index and concentration [on hold]

what does the gradient of the graph of refractive index against solution concentration mean
63 views

### Conformal Gravity

Lubos, in his comment to a question, says that (http://physics.stackexchange.com/q/61281) First of all, one can't gauge a symmetry without modifying (enriching) the field contents. Gauging a ...
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 $|S\uparrow\rangle$, $|S\downarrow\rangle$, $|X\uparrow\rangle$, $|Y\uparrow\rangle$, $|Z\uparrow\rangle$, ...
15 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 ...
44 views

### Why $U(1)_Y$ hypercharge rather than $U(1)_\text{em}$ electromagnetism?

In the Standard Model we have $SU(2)_I\times U(1)_Y$, where $U(1)_Y$ is weak hypercharge and $SU(2)_I$ is the symmetry group of weak isospin. Why do we introduce $U(1)_Y$ of weak hypercharge rather ...
26 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?
26 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 ...
79 views

35 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), ...
27 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 ...
44 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, ...
7k views

### Why would a spinning space station create a centrifugal force on an astronaut rather than simply spinning around him/her?

We often see films with spinning space station that create artificial gravity by having the astronauts pulled outwards by centrifugal force. I'd like to know if this would really happen, and if so, ...
70 views

38 views

### Global and relative phases of kets in QM

In one of the questions I'm trying to solve it is asked to, first, compute probabilities for the respective results of the Stern-Gerlach measurements performed on each state $\lvert\psi_1\rangle$, ...
815 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 ...
28 views

### Temperature of a single dipole [duplicate]

When taught about the temperature of a system from an illustrative point of view, I was told to think of molecules vibrating and hitting one another. If the molecules vibrate faster and faster (and in ...
82 views
+100

### Thermodynamic equilibrium - will the piston move?

Friend asked me this question and I didn't manage to solve it with basic thermodynamic reasoning. I believe this problem is easly solvable via numeric methods by choosing specific systems, though I ...