0
votes
1answer
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 ...
0
votes
0answers
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 ...
0
votes
0answers
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 ...
-1
votes
0answers
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 ...
0
votes
0answers
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 ...
1
vote
0answers
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?
0
votes
0answers
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 ...
0
votes
0answers
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 ...
0
votes
0answers
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 ...
0
votes
1answer
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?
-1
votes
0answers
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 ...
1
vote
2answers
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 ...
20
votes
6answers
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 ...
0
votes
2answers
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?
-3
votes
1answer
14 views

Relationship between refractive index and concentration [on hold]

what does the gradient of the graph of refractive index against solution concentration mean
6
votes
1answer
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 ...
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 $|S\uparrow\rangle$, $|S\downarrow\rangle$, $|X\uparrow\rangle$, $|Y\uparrow\rangle$, $|Z\uparrow\rangle$, ...
0
votes
1answer
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 ...
1
vote
2answers
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 ...
-2
votes
0answers
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?
0
votes
1answer
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 ...
3
votes
1answer
79 views

Energy-momentum tensor transformation [on hold]

I've been trying to find how the energy-momentum tensor changes if we add a total derivative to the lagrangian: $$L\to L+\mathrm d_\mu X^\mu.\tag{1}$$ From the answer key: $$T^{\mu\nu}\to ...
1
vote
0answers
31 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
60 views

Why is angular acceleration of a pendulum always negative?

I was trying to derive using the Lagrangian the equations of motion of a simple pendulum under the influence of gravity. Eventually, I was brought to this conclusion: $$\alpha = -(g\sinθ)/l$$ where ...
1
vote
0answers
11 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? ...
0
votes
1answer
72 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 ...
0
votes
0answers
16 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 ...
2
votes
0answers
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), ...
1
vote
0answers
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 ...
1
vote
2answers
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, ...
43
votes
4answers
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, ...
3
votes
0answers
70 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) = ...
5
votes
1answer
179 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 ...
2
votes
0answers
46 views

Scalar Curvature of a Conformally Flat Metric

Suppose that you have a metric $g_{\mu\nu}=\phi^2\eta_{\mu\nu}$ for some function $\phi$. There is a standard formula for what the scalar curvature $R$ looks like in terms of $\phi$, which is given by ...
-1
votes
1answer
19 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
1answer
50 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
0answers
26 views

Linearized Einstein equation on a general background metric

All of my texts only give the Linearized Einstein equation on the Minkowski background so I thought I'd try and figure it out by hand today. Using the standard perturbation $h_{\mu\nu}$ and denoting ...
0
votes
0answers
22 views

Natural light concentration [on hold]

Is it possible to use a stack of conical lenses to bring natural light to a specific focus and from there take it through optical fibers for illumination.
4
votes
1answer
39 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 ...
0
votes
0answers
15 views

What is this “outgrowth” on air tube in tonometer? [on hold]

I found the following "outgrowth" in air tube in electronic tonometer: The hole is apparently closed and air doesn't go out of it when tonometer pumps air inside. What is it for? Isn't it for ...
0
votes
1answer
29 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 ...
0
votes
0answers
16 views

The effects of multi-stranded wire on magnetic field strength

If I were to make a solenoid (with an air core) out of stranded copper wire- say for instance 8 strands- would this effect the magnetic field strength compared to, say, a solenoid with a single stand ...
0
votes
0answers
13 views

Directivity of dipole antennas inconsistency

I'm trying to model the directivity of dipole antennas of differing lengths. There are two main ways I've thought to approach this. The predicted radiation pattern is given by ...
0
votes
2answers
71 views

About de Broglie relations, what exactly is $E$? Its energy of what?

Well, you may know de Broglie relations, here they are: $$ E = h\nu, \quad\quad p = \frac{h}{\lambda} $$ My question is simple: What exactly is $E$? Is it the total energy? Maybe only kinetic energy? ...
0
votes
1answer
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 $\lvert\psi_1\rangle$, ...
8
votes
2answers
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 ...
0
votes
0answers
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 ...
3
votes
4answers
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 ...
0
votes
0answers
37 views

Why does scratching a blackboard gives such a painful noise?

I think we all have heard that terrible sound coming from scratching a blackboard with your nails. How is it produced? Has it something to do with the length of our nails?
0
votes
0answers
23 views

Electric potential due to something

What is the diffrence between "electric potential at some point due something" and "electric potential of something" ?

15 30 50 per page