2
votes
2answers
237 views

How do electrons get a charge?

Electrons belong to a group of elementary particles called leptons. There are charged and neutral leptons. And electron is the charged one. But how come it got charged? The negative or positive ...
-1
votes
0answers
17 views

Magnetic field direction, Lorentz force direction?

I know that the direction of current flow can change the direction of Lorentz force, what about the direction of the magnetic field? Also, for induced current due to electromagnetic induction is the ...
0
votes
1answer
40 views

How can electric field representation be obtained from Enge representation using Maxwell's equations?

Suppose we have a long electric capacitor. Let $L$ be its length ($z$ coordinate), $W$ its width ($y$ coordinate), and $D$ its full height (full aperture; $x$ coordinate). Let $L\gg W\gg D$. The ...
0
votes
1answer
17 views

Running Euler's disk in a superfluid

I was considering the toy Euler's Disk, a video can be found here: http://www.youtube.com/watch?v=mVl2CBG_h2s I was interested in understanding the behavior of the disk particularly in vacuum and in ...
14
votes
5answers
588 views

What was the entropy of the universe at the time of the Big Bang?

(I asked this question in Philosophy.SE; but I was advised to direct it here, despite it is, in my opinion, somewhat too speculative for physics.SE). High entropy generally means high disorder; and ...
1
vote
2answers
456 views

Why does weak equivalence principle say gravity is equivalent to acceleration?

I am told that the weak equivalent principle, that $m_i=m_g$ (inertial and gravitational masses are equivalent) is equivalent to the statement that in a small system you can't tell whether you are in ...
1
vote
1answer
50 views

Can a spacetime solution in GR have no Killing vector fields?

Sometimes Killing vector fields in a given spacetime are described as giving information about a symmetry of that particular spacetime solution. If I look at the requirement of a Killing vector field ...
2
votes
1answer
266 views

Geodesic equation from Euler - Lagrange

There are several ways to derive the geodesic equation. One of which is the variational method which I seemed to understand it because it was written in great details. Then it was mentioned that the ...
1
vote
1answer
25 views

Is there a material that could “convert” near infrared frequency to infrared?

I have a laser with a wavelength of 650 nm (visible red light) and was wondering if there is some sort of material that could be used to absorb and disperse a different frequency of light around (900 ...
4
votes
1answer
117 views

Is WKB really applicable for the ground state?

It is a long time question for me. For me, it seems that WKB is applicable for a given $E$ if and only if $\hbar$ is sufficiently small. Or in other words, WKB is applicable if and only if the ...
0
votes
1answer
25 views

Making water spin a wheel [on hold]

Let's say that I have a wheel with 8 symmetric arranged rectangular plates of area $A$ and the water, with density $\rho$, in the river it moves with $v\: \mathrm{m/s}$. How do I calculate the ...
1
vote
1answer
12 views

Do two engines with the same specific impulse always perform the same amount of work?

As the title say, do engines with different thrusts with the same $I_{sp}$ and the same amount of fuel perform the same amount of work?
0
votes
0answers
14 views

Filtering UV Light to Visible Light [on hold]

I'm wondering if it is physically possible to filter UV light from 400nm to 100nm so that UV light is in the visible range. If we had a UV screen over a visible range screen, could there be two ...
-1
votes
0answers
18 views

Pion-Pion One-Loop Scattering Amplitude? [on hold]

What is the one-loop pion-pion scattering amplitude (with finite pion mass)?
-3
votes
0answers
20 views

What is a good (e-)book on flight dynamics, guidance, and navigation? [on hold]

I want to buy a detailed theoretical foundation book on flight dynamics, particularly geared towards navigation. Is there any solid comprehensive material?
1
vote
0answers
26 views

Non-Darcy Flow : Forchheimer plotting method

Recalling Darcy's equation for gas flow, assuming ($z\mu_g$) = Constant $$\tag{1} q_{g,sc}=\frac{kA}{L}\left(\frac{T_{sc}}{Tp_{sc}}\right)\left(\frac{1}{2z\mu_g}\right)(p_1^2-p_2^2)$$ For ...
17
votes
1answer
175 views

Fluctuations of an interface with hammock potential

This question is related to that one. I ask it here since comments are too short for the extended discussion that was going on there. I am interested in a very simple interface model. To each ...
0
votes
1answer
46 views

Does inducing charge on a grounded conductor do work?

Imagine a grounded conductor as an plane of infinite area. If I bring a charge to a close proximity to the plane, it induces some charge distribution on the conductor. The question is: is any work ...
-3
votes
3answers
71 views

Can you die from a $250 \, \mathrm V$ broken cable? [on hold]

I have a laptop power cable that is broken, my dad taped it so it is safe now. I am just wondering: would it have killed me had I touched it? If you could state your qualification/job to show you ...
4
votes
1answer
257 views

Scaling with the Ising Model

I am stuck with one formula in the CFT book by Di Francesco and al. Chapter 3. Equation 3.46 third step, for those who don't have the book, he integrates out degrees of freedom from the Ising Model by ...
1
vote
1answer
204 views

Energy difference between symmetric and antisymmetric wavefunctions [on hold]

Is there any energy difference between a particle in a symmetric wavefunction and an identical particle in an identical potential but in a state with an anti-symmetric wavefunction? Or is it ...
1
vote
1answer
38 views

Does polarization remove any of the fields completely?

A light is made up of electric and magnetic fields oriented perpendicular to each other. Can polarization lead to the removal of any of the fields completely?
15
votes
2answers
2k views

Why don't we have a theory of everything?

What is currently stopping us from having a theory of everything? i.e. what mathematical barriers, or others, are stopping us from unifying GR and QM? I have read that string theory is a means to ...
1
vote
3answers
1k views

Can internal forces do work?

My Mechanics textbook claims that the sum of the work by internal forces is not generally zero. translated to English the paragraph reads: Notice about the work by internal forces: the work by ...
0
votes
1answer
20 views

What type of glass is used in oven glass doors? [on hold]

I understand that the glass used in convection oven door must be able to withstand high heat. But what should be the exact specification if I am thinking of replacing my broken oven door and ...
2
votes
3answers
75 views

What's the difference between frequency domain and time domain spectra?

If I have a mechanical oscillator and want to observe the dynamical behavior of the oscillator, is there any additional information to observe it in time domain and frequency domain? Normally, we ...
2
votes
3answers
330 views

Plants and Quantum Mechanics!

So, I have been working on quantum biology and found something interesting that I would like to write an equation for: Scientists have wondered how plants have such a high efficiency in ...
2
votes
0answers
45 views

Lorentz transformation - Bjorken & Drell

I'm trying to derive (14.25) in Bjorken & Drell (B&D) QFT. This is $$\tag{14.25}U(\epsilon)A^\mu(x)U^{-1}(\epsilon) = A^\mu(x') - \epsilon^{\mu\nu}A_\nu(x') + \frac{\partial ...
1
vote
2answers
69 views

How does electrostatic force affect electronic devices?

How does electrostatic force generated by two seperate plates having opposite charges affect electronic devices? I know that magnetic fields have some harmful effects to electronic devices but I am ...
3
votes
2answers
80 views

What materials are used in non thermal plasma?

While reading about non-thermal plasmas, I came across their ionization potentials(~1%), and other capabilities, such as their non Maxwellian energy distributions. At what temperatures, and pressures ...
1
vote
1answer
24 views

How do you work out the energy requirement for a submerged pump?

I was wondering if you were to place a pump in a submerged container and then were to open a hatch allowing water to flood the previously vacant cavity how much energy would be required to discharge ...
24
votes
2answers
2k views

I touched a tree that was touching an electric fence and got an electric shock. How is this possible if wood is an insulator?

I touched a tree that was touching an electric fence and got an electric shock. How was this possible if wood is an insulator? The tree wasn't wet either, and it was a pretty strong shock too.
1
vote
1answer
106 views

Reproductibility of the effects described in US patent 8,419,919

US patent 8,419,919, by P. Boss, F. Gordon, S. Szpak, and L. Forsley, describes what (I summarize) would be a method to perform particle generation leading to atomic transmutation, by palladium ...
0
votes
0answers
17 views

What is the physical process in paramagnetic resonance

In our QM lectures, Prof introduced an phenomenon called paramagnetic resonance, which described an electron precession in an $z$-direction magnetic field. I didn't quite understand this phenomenon, ...
2
votes
2answers
83 views

How would gravitons couple to the Stress-Energy tensor?

How would gravitons couple to the Stress-Energy tensor $T^{\mu\nu}$? How did physicists arrive at this result? I've read that it follows from the analysis of irreducible representations of the ...
3
votes
1answer
161 views

What near-future measurement technique improvements will extend our physical knowledge?

Inspired by the wiki-article on atom-lasers: Another application, which might also benefit from atom lasers, is atom interferometry. In an atom interferometer an atomic wave packet is ...
0
votes
1answer
27 views

How do I calculate the right ascension of the points along the ecliptic at given elevations?

How do I calculate the right ascension of the point along the ecliptic nearest the sun at sunset and sunrise that is at a given altitude/elevation? For example, I'd like to compute the right ...
0
votes
0answers
16 views

Soft Scalar Emission [on hold]

For a massless spin particle $\phi$ which has an interaction Lagrangian density of the form $\phi(x)J(x)$, where $J(x)$ contains only massive particles fields, what is the rate of emission of soft ...
2
votes
1answer
49 views

Curvature of a particle move

I'm simulating a particle movement following a normal distribution. How this is done: My particle has a constant speed v and every step the particle move, I ...
0
votes
1answer
135 views

Reciprocal Lattice of a non-bravais lattice

Is a reciprocal lattice defined for non-Bravais lattices? I'm trying to work out one for HCP structure and not figuring it out.
1
vote
1answer
76 views

Can I tune a magnetic field to conduct heat from a rotating object?

Is there a way to transfer heat from a rotating object made of iron into a suitable heat sink using a magnetic field as a transfer medium?
0
votes
0answers
18 views

Spectral Decomposition for Complex Conserved Current [on hold]

What is the spectral decomposition for the vacuum expectation value of a complex conserved current $J^\mu(x)$, $\langle T\{J^\mu(x),J^\nu(y)^\dagger\}\rangle$?
2
votes
1answer
504 views

Minimal vs. Non-minimal coupling

What is the difference between Minimal vs. Non-minimal coupling in General Relativity? A brief introduction to Minimal Coupling in General Relativity could be useful too.
1
vote
1answer
135 views

If a car appears in horison and within 2 seconds passes you by, whats the speed it's doing?

While watching the first 4 seconds of driving at 745 km/h is ludicrous from any angle wondered If we knew the curvature of the Earth in a "flat" desert, what would be the speed of the car? ...
10
votes
1answer
162 views

The status of the BICEP2 'discovery' after Planck 2014

The tumultous period after the original announcement that the BICEP2 experiment had supposedly detected strong evidence of cosmological inflation in the form of B-mode polarization in the cosmic ...
2
votes
2answers
61 views

Higher rank $\gamma$-matrix question

I read that the higher rank $\gamma$ matrices can be written as alternate commutators and anti-commutators. For example, the rank 3 gamma matrix can be written as $$\gamma^{123} = ...
2
votes
1answer
60 views

Electron/positron annihilation lines in astrophysics

I have a reasonable understanding of electron/positron annihilation, in that it is a collision between a pair of particles, one matter and one antimatter, that generally produces gamma radiation. ...
0
votes
0answers
23 views

Interference of sound: how to calculate the sound intensity at each point?

I need help with the following question: Two speakers are sending out sound in phase with the frequency 2,13 kHz. The sound from the speakers is registered in three points A, B and C. See figure. ...
6
votes
1answer
69 views

Twin paradox, different starting locations

Let's say I have a twin who is at rest relative to myself and ten light years away from me, we are both in rocket ships. We have agreed that I will send a laser pulse and that when he receives it we ...
1
vote
0answers
12 views

How come plasmon resonances of metals are capable of being tuned to different wavelengths?

I read in this article that plasmon resonances though being a pre-determined property of a metal are capable of being tuned to other wavelengths when these same metals are made into tiny ...

15 30 50 per page