# All Questions

276 views

### Determining the capacitance of a system with a non-homogenous dielectric

In an experiment we were given non-homogenous dielectric substances described by functions of coordinate. How can capacitance be determined from this?
172 views

### Renormalization Group for anisotropic “Gaussian” model

I'm considering an "anisotropic" Hamiltonian of the form $$\beta H = \int d^n r_{||} d^{d-n} r_{\bot} \frac{K}{2} (\nabla_{||} m)^2 + \frac{L}{2} (\nabla^2_\bot m)^2 + \frac{t}{2}m^2 - hm$$ which in ...
1k views

### Counter Rotating Bicycle wheels on same axis-> Will they still cause me to spin on a stool?

So people are familiar with the idea of holding a spinning bicycle wheel while on a stool (whose seat can spin). You then tilt the spinning wheel and lo and behold you start to spin on the stool. Ok ...
2k views

### Total Resistance of Infinite Resistor Grid?

The problem of the infinite resistor grid is very common. The solution for the resistance between any 2 nodes in an infinite resistor lattice is all over the internet. My question is somewhat similar ...
780 views

### Simplified partial trace of two operators

If I have two operators A and B living in the Composite Hilbert Space $H_I \bigotimes H_{II}$ and I want to take the partial trace of $C=AB$ over the subspace $H_I$, i.e., $Tr_I[AB]$, is there any ...
134 views

### Which low energy SUSY models are compatible with LHC and tevatron data so far?

The LHC data has eliminated huge swaths of permissible low energy SUSY breaking models. But not all. Which regions of parameter space are still open?
268 views

### What is deep Fresnel region?

If I understand correctly, it has something to do with autocorrelation function, but can someone give me a definition or exact explanation? In case of scattering, if you wish to analyze pattern with ...
3k views

### Metric tensor of coordinate transformation

How do you find a metric tensor given a coordinate transformation, $(t', x', y', z') \rightarrow (t, x, y, z)$? Our textbook gives a somewhat vague example as it skips some steps ...
803 views

### Galilean transformation in relativity

Assume flat spacetime in a general relativistic framework (or special relativity for that matter) and two observers $A$ and $B$, with non-vanishing velocity relative to each other. We know that they ...
2k views

### Force on rope with accelerating mass on pulley

I have a pretty basic pulley problem where I lack the right start. A child sits on a seat which is held by a rope going to a cable roll (attached to a tree) and back into the kid's hands. When it ...
101 views

### Creation of Nuclear Isomers

As I understand it, if a nucleus is excited with energy exceeding its ground state, it releases energy via gamma radiation. An example would be technitium 99m, a medical tracer with a 6 hour half life ...
5k views

### Voltage and Current in transformers

In transformers, the ratio of the voltages equals the ratio of the turns - so double the output coil's turns and the output voltage doubles. Then, in order to conserve energy, current halves. This ...
298 views

### Why every galaxy is moving away from every other galaxy on astronomical scale? because of an explosion or because of creation of space?

Why galaxies move away from each other in general on the astronomical scale? Which answer is correct of the following? It is because of the big bang theory, everything is just moving away from ...
385 views

### Quantum phenomena near black hole event horizon

I wanted to re-open the question of quantum measurements across event horizons. If I set up two slits or more generally a diffraction grating which crosses a black hole event horizon, and I shoot a ...
416 views

### Air drag coefficient value

Is there any equation that calculates the $C_d$ value in the formula of air drag ? $$F_d = \rho C_d v^2 A$$ I have found that there are tables for this constant but I am looking for the equation that ...
480 views

### What happens to speed and frequency of a light beam moving in transparent medium when observed from different inertial frame of reference?

Suppose a transparent medium where speed of light is $c/n$, an inertial frame of reference $K$ which is stationary relatively to the medium and an inertial frame of reference $K'$ which is moving ...
6k views

### What is “quantum locking”?

I've always assumed that "quantum locking" was a term invented by the writers of Dr Who, but this video suggests otherwise. What is quantum locking? Is it real?
2k views

### How may the magnetic resistance for a magnet moving through a copper pipe be calculated?

When a magnet moves past non-magnetic, electrically conducting material such as copper, the changing magnetic field induces electric eddy currents in the copper, which create their own magnetic field ...
243 views

### Are Everettian branchings global or local?

Everett's theory of quantum mechanics is about the wavefunction of the whole universe holistically. If a branching occurs very far away at the Andromeda galaxy, do I also branch? Are branchings global ...
279 views

### Would a strong diamagnetic material exhibit inductance?

Do metals with the property of strong diamagnetism also exhibit inductance? Would a fluctuating magnetic field induce a weaker current in a strongly diamagnetic metal as compared against a ...
539 views

### Why does the speed of light within a solid depend on frequency?

Different frequencies of light travel at different speeds through solids, which along with Snell's law allows for rainbows. Has this phenomenon of variable speeds been predicted through derivations? ...
214 views

### Degeneracy and the Hamiltonian

How many linearly independent eigenfunctions can be associated with one degenerate eigenvalue of the Hamiltonian operator? (Is there a limit since it contains a 2nd order differential operator?) ...
436 views

### Why we don't see long range airborne CO2 lasers?

I wonder, why http://en.wikipedia.org/wiki/Boeing_YAL-1 is not CO2 one? Are the issues with air transparency at 10um? Or it's impossible to focus on large distances due to diffraction?
1k views

### Effects of high frequency lighting on human vision?

I have a couple of different LED flashlights. One of them has three different "modes" of brightness, and the way it controls it is via pulse width modulation (PWM). Here is a picture that illustrates ...
594 views

### What is a nonlinear field?

I have read two possible definitions. A nonlinear field is A field taking values on a manifold. A field whose equation is nonlinear. What do you understand by a nonlinear field or a nonlinear ...
8k views

### Best way to solve P-V-T Question

Typically in an exam or problem set we have a problem that's like this: Determine the specified property at the indicated state of water. Locate the state on a sketch of the T-v and P-v diagram. p= 3 ...
442 views

### How to determine the required resolution to view an image at a certain size?

If I have several camera specifics, can I determine the required resolution to view an image at the size I want? For example, let's say I want a picture of a square painting to be at least ...
273 views

### Looking for specific Relativity example

Many years ago (in the '70s I think) I read an explanation of the meaninglessness of simultaneity at large distances. The example had to do with two people walking along a sidewalk in opposite ...
302 views

### In continuum mechanics, what is work potential in the context of total potential energy?

I'm reading a book on the finite element method. Specifically I'm looking at the background material where they are discussing potential energy, equilibrium, and the Rayleigh–Ritz method. The book ...
179 views

### What is a proton-rich atom?

http://wiki.chemprime.chemeddl.org/images/e/e4/Plot_of_Neutron_Number_vs._Proton_Number_.jpg The above graph shows that all elements have more neutrons than protons in this nucleus. So how is there ...
2k views

### What will the strength of a sintered steel piece be compared with a cast piece?

By sintering here, I mean specifically deposition laser sintering, i.e., put down a patch of steel powder, zap it with a laser so that it liquifies at least partially, lay down a new patch, laser, ...
385 views

### Why does gravity forbid local observables?

I heard in a conference that gravity forbids to construct local gauge invariants like $\mathrm{Tr}\left\{−\frac{1}{4} F_{μν}^{a}F_{a}^{μν}\right\}$ and only allows non-local gauge invariant quantities ...
72 views

### stress work of uniformly deforming continuum

I have a volume which is deforming (using explicit time-integration scheme) uniformly with velocity gradient $L$ and stress tensor $\sigma$. I would like to determine work done by the volume ...
149 views

### Confusion with the torque

Consider an imaginary vertical plane. Now say, a body is falling freely (under earth's attraction). If you consider any axis that is perpendicular to that plane. We get a non-zero value for torque. ...
713 views

913 views

### What is the conserved canonical momentum for a relativistically moving charge in a static Coulomb electric field?

The canonical momentum is a fundamental conserved quantity from Noether's theorem for translational invariance of the Lagrangian. Yet I'm finding it very difficult to see its derivation, or even a ...
2k views

### Stress vs Strain for mild steel

After Yield point on stress strain diagram the under curve occurs what does it mean what will happen for the mild steel at that particular time and again why the curve goes to up and reaches ...
503 views

### Wave equations & propagation theories

I'm interrested in making computer simulation but I've run into rather physics oriented problem. I have to choose how to propagate my wave. Though I've found technique called FDTD (finite-difference ...

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