question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<ol>
<li><p><strong>Free field theory:</strong> Why is it said that different Fourier modes in case of a free field (say, real Klein-Gordon field) are independent of each other?</p></li>
<li><p><strong>Interacting field theory:</strong> How exactly does the addition of non-linear term in the Lagrangian make the Fouri... | 2,438 |
<p>Why is <a href="http://en.wikipedia.org/wiki/Earnshaw%27s_theorem" rel="nofollow">Earnshaw's Theorem</a> inapplicable for moving ferromagnets?</p>
<p>Can I get a mathematical classical proof for this?</p> | 2,439 |
<p>I am wondering if I mix up the notion of <em>proper distance</em> and <em>proper length</em>.</p>
<p>I have two cuves in Schwarzschild space-time describing the flight of two photons (think of it as photons guided in by optical fiber, not geodesics).</p>
<p>$\gamma_1(\lambda) = \big(t_1(\lambda),r_1(\lambda),\frac... | 2,440 |
<p>I am trying to follow the steps to solve the integro-differential equation that arises from a plasma sheath problem given in <a href="http://scitation.aip.org/content/aip/journal/pop/13/11/10.1063/1.2388265" rel="nofollow">this paper</a>. This is the step I can't follow:</p>
<blockquote>
<p>$$\epsilon_o\frac{d}{d... | 2,441 |
<p>I have $N$ distinguishable particles in a 1D harmonic oscillator potential with 'proper' frequency $\omega$. The particles also have internal spin-$\frac12$ degrees of freedom in a magnetic field $B$ with magnetic dipole $\mu$. The spin induced energy level splitting is
$$\varepsilon=2\mu B=0.1\hbar\omega$$</p>
<b... | 2,442 |
<p>For example say the gravitation constant instead of equaling G, was actually a range bounded between 0 and infinity. </p>
<p>Our Universe would be at a point on this range (equal to our G value) where things could physically exist and produce stars, galaxies and life. Yet in the gravitation constant's dimension it ... | 2,443 |
<p><img src="http://i.stack.imgur.com/gQ3jg.gif" alt=""></p>
<p>I recently stumbled upon the above image describing partial transmittance, and was wondering what sort of equation would model such a wave propagating through varying mediums. Is there also an equation for continuous mediums, as opposed to the discontinuo... | 2,444 |
<p>In the book <a href="http://books.google.ca/books?id=UaY1MLmC780C&printsec=frontcover&source=gbs_atb#v=onepage&q&f=false" rel="nofollow">Nonlinear Optics</a>, it is stated that the nonlinear effects start to become a problem in WDM systems (around 1550 nm) after about 1 mW of optical power. However, ... | 2,445 |
<p>Assume a balloon filled with Hydrogen, fitted with a perfect valve, and capable of enduring vacuum (that is to say, it would retain it's shape and so well insulated that the extremes of temperature at high altitudes and in space would have little effect) were to be launched. </p>
<p>As long as the balloon were in a... | 2,446 |
<p>I'm reading about how the soon-to-be-launched <a href="http://en.wikipedia.org/wiki/Nuclear_Spectroscopic_Telescope_Array" rel="nofollow">NuSTAR</a> is on the cutting edge of focusing x-rays, which captures 5 to 80 keV radiation by focusing them with optics that have a 10.15 meter focal length onto 2 sets of 4 32×32... | 2,447 |
<p>The text I am reading (Stars and Relativity by Ya. B. Zel'dovich) discusses the possible existence of a repulsive force proportional to total baryon number. At the time of the book's publication it was stated that if such a force existed, it woukd need to be on the order of $10^{46}$ times weaker than the Coulomb fo... | 2,448 |
<blockquote>
<p>What are some common applications, uses, exploitations of the properties of surface tension? </p>
</blockquote>
<p>Here is what I mean. A water strider can walk on water, that is a consequence of surface tension. This is a consequence, but it is not human made.</p>
<p>On the other hand, I heard that... | 2,449 |
<p>English Wikipedia in the <a href="http://en.wikipedia.org/wiki/Poisson%27s_ratio#Width_change" rel="nofollow">Poisson's ratio article</a> gives an equation for large deformation:
$$
\frac{\Delta d}{d}=-1+\frac{1}{\left(1+\dfrac{\Delta L}{L}\right)^\nu}
$$</p>
<p>I couldn't find any reference for this equation. Co... | 2,450 |
<p><em>It's really shocking that the following question was voted down twice although the question is yet to be answered by anyone.</em></p>
<p>So please read the following and give an answer why physics community has taken a double standard in the following case.</p>
<p>We know about Michelson's experiment. We also ... | 2,451 |
<p>I've been lightly studying GR lately. Something that has been bothering me has been the lack of (Ricci) curvature produced from the Schwarzschild metric in the few lectures I've watched, as well as the few snippets of text book I've been able to read. Why is there no (Ricci) curvature outside this spherically symmet... | 2,452 |
<p>Now consider I went into a rocket which goes an infinite distance far from earth. By infinite I mean very far. The gravitational attraction between me and the earth will significantly decrease and after a certain distance it will cease to act as the inertia of my rocket would be bigger than the gravitational force b... | 2,453 |
<p>I have a strong background in Fourier analysis, and I'm looking for QM resources that can build on that. Is there a book around or a little above the level of Griffiths that has that kind of emphasis? Any other resources are good too.</p> | 2,454 |
<p>The question basically amounts to whether I can construct the illusion of superposition with adjacent sine waves of varying frequency.</p>
<p><strong>Context</strong></p>
<p>I'm trying to play music on a Tesla Coil (like OneTesla and the works). If I want to play an A for instance, I'll modulate my input signal so... | 2,455 |
<p>I'm programming a 1 dimensional physics simulator in python. How do I calculate the amount of time until two particle points that are traveling towards eachother collide? I am using the equation: </p>
<pre><code>time = (m2.pos - m1.pos) / (m1.velocity - m2.velocity).
</code></pre>
<p>You can assume m1 is always o... | 2,456 |
<p>I'm working my way through Griffith's "Introduction to Electrodynamics". In Ch. 10, gauge transformations are introduced. The author shows that, given any magnetic potential $\textbf{A}_0$ and electric potentials $V_0$, we can create a new set of equivalent magnetic and electric potentials given by:</p>
<p>$$
\text... | 2,457 |
<p>There are known formulae relating a capacitor's voltage and current in its classic form (battery, wires, a capacitor circuit), but what if we had a charged plate (-ve), then we put on one of its surfaces a dielectric, then we put another plate (neutral, connected to the ground)? </p>
<p>Technically, this is a capac... | 2,458 |
<p>I'm trying to calculate the induced $-V$ in a DC circuit when current starts to flow, and reaches it's maximum value.
The inductance of the conductor is 1000nH it carries large amounts of current (1000A), what formula is best to know the $-V$ due to self inductance?</p> | 2,459 |
<p>I want to understand the derivation of the partition function for two distinguishable non-interacting particles. </p>
<p>Let the energy of particles $1$ and $2$ be $E_1$ and $E_2$ respectively. Setting $\beta = 1/kT$, the partition function becomes:
$$
Z = \sum_{s} e^{-\beta[E_1(s)+E_2(s)]}
$$
Where $s$ represents ... | 2,460 |
<p>What does the following mean with respect to <a href="http://en.wikipedia.org/wiki/Special_relativity">special relativity</a>?</p>
<p>$$\frac{1}{\sqrt{1 - \frac{v^2}{c^2}}}$$</p> | 2,461 |
<p>If one is able to travel into the past but at a spatial distance that puts him outside of his own past light cone would this be considered a causality violating trip? Looking at a Minkoski diagram, it would seem that one ought to be able to travel to a spatially displaced past without producing causality violations.... | 2,462 |
<p>I was reading up on the history of the solar neutrino problem, and as far as I can understand it, neutrinos supposedly oscillate from one form to another, thus explaining why there were only one-third the number of neutrinos detected than were expected, when they began neutrino observations in the 1960's.</p>
<p>Th... | 2,463 |
<p>It is claimed that <a href="http://www.google.com/#q=de+Sitter+temperature" rel="nofollow">de Sitter temperature</a> is $$T=\frac{1}{2\pi}H,$$</p>
<p>where $H$ is the Hubble constant. I presume it is expressed in natural units with which I am not familiar. So what it will be in Kelvins? Is it higher than the temper... | 2,464 |
<p>We know that level-k Abelian 2+1D Chern-Simons theory on the $T^2$ spatial torus gives ground state degeneracy($GSD$):
$$GSD=k$$</p>
<p><strong>How about $GSD$ on $T^2$ spatial torus of</strong>: </p>
<p><strong>SU(N)$_k$ level-k Chern-Simons theory?</strong></p>
<p><strong>SO(N)$_k$ level-k Chern-Simons theory?<... | 2,465 |
<p>I know classical physics, quantum mechanics, special relativity, basic nuclear physics.
I would like to get into some particle physics. </p>
<p>I want to get into that higgs boson, lepton, quark things :D </p>
<p>Where to start? Any books, websites, video lectures? </p>
<p>Mathematical rigor required! </p>
<p>T... | 154 |
<p>Why is it that when we cut bread or anything else with a knife, the less effective way to cut it is just by pressing on it from above? And is it true that we can cut things with knife because of the thin edge that makes an interaction with the other material (like bread)?</p> | 2,466 |
<p>Quantum Mechanics is very successful in determining the overall statistical distribution of many measurements of the same process.</p>
<p>On the other hand, it is completely clueless in determining the outcome of a single measurement. It can only describe it as having a "random" outcome within the predicted distrib... | 2,467 |
<p>$g\phi^3$ , $d=4$ , 3 point One loop diagram (three external legs) Divergence</p>
<p>I am trying to find where the divergence factor/pole is on the following diagram in 4 dimensions so that I can use minimal subtraction...</p>
<p><img src="http://i.stack.imgur.com/lV1cy.png" alt="enter image description here"></p>... | 2,468 |
<p>Given reflectivity $R = 0.75$, an etalon is used as an interference filter, transmitting light of wavelength $4.3\mu m$ at normal incidence. The full width half maximum is about $\Delta \lambda = 0.2 \mu m$. Find the initial spacing of plate.</p>
<p>(a) Find the spacing of the plate.</p>
<p>(b) Find the change in ... | 2,469 |
<p>I've had it explained to me in a <a href="http://physics.stackexchange.com/questions/117013/is-there-a-difference-between-photons-that-act-as-virtual-particles-and-photon">separate post</a> that charged particles are constantly exchanging virtual particles with other charged particles and their energy is a steady st... | 2,470 |
<p>I always thought that $force$ is $mass * acceleration$. Well, that's what I learnt at school a while back. Now, I have been enlightened that force is in fact the rate of change of momentum. </p>
<p>What makes this interesting to me, is that this takes into account a change in mass with respect to time as also playi... | 47 |
<p>This question is related to the Big Bang Nucleosynthesis of light elements, more concretely I do not understand some features of the graph</p>
<p><img src="http://i.stack.imgur.com/GSfcM.png" alt="BBabundances"></p>
<ul>
<li><p>Why do the $^3$He and D abundances go down with increasing baryon to photon fraction wh... | 2,471 |
<p>How does sub-ambient cooling work?</p>
<p>There are water cooling systems for computers that can cool components to below room temperature. The problem I see here is that the water is cooled using room temperature air. How can the cooling system keep a 150 watt computer component at a temperature below room tempera... | 2,472 |
<p>I have a model that represents a bicycle (a wood block with wheels), and I'm balancing the center of gravity so it's the same as a real bike. However, when the center of mass is kept constant, does the weight of it affect the effect torque has on it when it hits a wall?</p>
<p>I'm planning to measure the angle the ... | 2,473 |
<p>Order parameter is used to describe second order <a href="http://en.wikipedia.org/wiki/Phase_transition" rel="nofollow">phase transition</a>. It seems that in some papers it is used in the first order phase transitions. Can first order phase transition have an order parameter? If so, how can we define the order para... | 2,474 |
<p>Dirac equation for the massless fermions in curved spase time is $γ^ae^μ_aD_μΨ=0$, where $e^μ_a$ are the tetrads. I have to show that Dirac spinors obey the following equation:
$$(−D_μD^μ+\frac{1}{4}R)Ψ=0\qquad(1)$$</p>
<p>where $R$ is the Ricci scalar.</p>
<p>I already know that $[D_\mu,D_\nu]A^\rho={{R_{\mu\nu}}... | 2,475 |
<p>It is well-known that Hooke's Law is only approximately true and thus that linear relation
is merely an idealization not strictly corresponding to the reality. Wouldn't it be necessary/appropriate that all linear relations decribing physical phenomena be reformulated to contain non-linear terms for use in cases wher... | 2,476 |
<p>I spent some time studying about temperatures and color of objects. It turns out that as we heat something it turns to red, then yellowish white and if we heat it more it turns to bluish-white.</p>
<p>Like we can say a blue star is hotter than a red star.
But why isn't it the same with flames?</p>
<p>Blue flame is... | 2,477 |
<p>According to <a href="https://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness" rel="nofollow">Wikipedia's article on the Mohs scale of mineral hardness</a>, materials / minerals with a higher rating cannot be "visibly" scratched by materials with a lower rating.</p>
<p>It goes on to admit that microscopic disl... | 2,478 |
<p>I can unterstand why because the integration over Grassman variables has to be translational invariant too, one has </p>
<p>$$
\int d\theta = 0
$$</p>
<p>and </p>
<p>$$
\int d\theta \theta = 1
$$</p>
<p>but I dont see where the rule for this double integration</p>
<p>$$
\int d^2 \theta \bar{\theta}\theta = -2i... | 2,479 |
<p>I consider an electron (charge $-e$) in $x=0$ and a constant electric field $E(x) \equiv E $. If the electron has initial velocity $v_0$ with the same direction of $E$, then its potential energy is
$$ U(x) = -eV(x) = -e E x $$
The total energy for $x=0$ is
$$ K(0) + U(0) = \dfrac{1}{2} m v_0^2 $$
Now if I try to obt... | 2,480 |
<p>I've recently seen that space is or could be a quantum vacuum full of particles like matter and anti matter appearing and possibly colliding causing in theory the same effects that dark energy has. My question is could Dark energy or dark matter be a left over waste product of matter/anti matter collisions? </p> | 2,481 |
<p>Basically, what are all the parameters that completely describe an electron in quantum theory.</p>
<p>In classical physics a complete and fundamental description of an electron is given by its mass, charge, and position. So $(m, q, \vec{x}(t))$ gives you complete information about the electron.</p>
<p>I would like... | 2,482 |
<p>The basic Randall-Sundrum model is given by the metric,</p>
<p>$$\mathrm{d}s^2 = e^{-2|\sigma|}\left[ \mathrm{d}t^2 -\mathrm{d}x^2-\mathrm{d}y^2 - \mathrm{d}z^2 \right]-\mathrm{d}\sigma^2$$</p>
<p>where $\sigma$ denotes the additional fifth dimension. Notice the brane is localized at $\sigma=0$; this 'slice' is pr... | 2,483 |
<p>They say <a href="http://en.wikipedia.org/wiki/Inflation_%28cosmology%29" rel="nofollow">inflation</a> must have occured because the universe is very homogeneous. Otherwise, how could one part of the universe reach the same temperature as another when the distance between the parts is more than light could have trav... | 2,484 |
<p>I have an 80 mm <a href="http://en.wikipedia.org/wiki/Refracting_telescope" rel="nofollow">refractor</a> telescope on a tripod, but it shakes on every touch. It's very hard to see via 6 mm (x120) ocular. Even a little wind causes the image to become too unsteady. </p>
<p>How can I make my tripod more stea... | 2,485 |
<p>I'm not an expert but I've come to understand that the universe is expanding at enormous speed. That means that all of the visible galaxies are moving away from us at great speed. </p>
<p>I also came to understand that, eventually (in many many years), all the galaxies and all of the rest of the objects outside our... | 2,486 |
<p>If general relativity is the newest model of Gravity which is so far been proven. Does it still have any anomalies such as the <a href="http://physics.stackexchange.com/q/26408/2451">problem</a> of Mercury's orbit during Newtonian gravity period?</p>
<p>If so are there other types of physics to be discovered?</p> | 2,487 |
<p>We can see that when a charge sphere is at rest & we are to put it in motion with any desired velocity than we will have to apply the same force for a longer time as if it were applied to the identical uncharged sphere to put it in motion with the same desired velocity.Here the due to electromagnetic fields asso... | 2,488 |
<p>So it's Thanksgiving here in the states and an odd combination of things are on my mind. In the past day, I've</p>
<ul>
<li>Brined a turkey whole, skin on</li>
<li>Taken a long epsom salt bath</li>
</ul>
<p>(Same thing, right? What a turkey! Haha.)</p>
<p>Anyways, it got me wondering, can a long salt water bath i... | 2,489 |
<p><strong>Question:</strong></p>
<p>Will this work as I've shown it here, more or less, or will the iron cylinder being hollow produce results not shown? </p>
<p><strong>Topic:</strong></p>
<p>I'm experimenting with magnetic fields and have been testing electromagnets. For a specific device that I'm interested in e... | 2,490 |
<p>The pressure cooker is heated at the base to cook the food. The pressure cooker releases steam when the force exerted by pressure exceeds the counterweight, at which point the weight rises up allowing steam to escape. The time to cook is measured by the number of times steam is released.</p>
<p>When food(dry lentil... | 2,491 |
<p>Hope this isn't something trivially wrong, I am a beginner in classical mechanics. But anyways, say there is a cube, of side length $a \ \text{cm}$. The volume of the cube is $a^3 \ \text{cm}^3$. If the total mass of the cube is $m \text{ kg}$, the <a href="http://en.wikipedia.org/wiki/Density" rel="nofollow">densi... | 2,492 |
<p>I had read somewhere that a star, whose light passes very close to the sun and reaches the earth produces 4 images of the same star (left, right, top and bottom) in a telescope due to gravitational lensing. However, this cannot be possible. Since light from the star passes on all sides of the sun (continuous 360 deg... | 48 |
<p>As far as I understand a new pattern of crystal growth has been found experimentally. How does it relate to the known 2D and 3D nucleation and growth of crystals? The dominating theory of crystal growth nowadays is that initiated by Cabrera and Frank. How is the new finding related to what we know so far or is it at... | 2,493 |
<p>When judging if relativity is important in a given phenomenon, we might examine the number $v/c$, with $v$ a typical velocity of the object. If this number is near one, relativity is important. In optics, we examine $\lambda/d$, with $\lambda$ the wavelength of light involved, and $d$ a typical size-scale for the ... | 2,494 |
<p>Suppose I do two experiments to find the triple point of water, one in zero-g and one on Earth. On Earth, water in the liquid or solid phase has less gravitational potential per unit mass than water in the gas phase. Therefore, the solid and liquid phases should be favored slightly more on Earth than in zero-g.</p... | 2,495 |
<p>I have a horizontal bar on vertical rails and we can consider that does not exist any friction. </p>
<p>Perpendicular to the plane of the rails it exists a magnetic field $B$. </p>
<p>I am asked to find the movement equations and the bar position depending on time. </p>
<p>And I have made some considerations: </p... | 2,496 |
<p>While reading about the <a href="http://en.wikipedia.org/wiki/Clausius-Clapeyron_equation" rel="nofollow">Clausius Clapeyron equation</a> from the Feynman lectures on Physics, I couldn't understand a few things from its derivation:</p>
<p>Although the argument was pretty clear, when the system consists both gas(vap... | 2,497 |
<p>In <a href="http://arxiv.org/abs/hep-th/0702178" rel="nofollow">this 2007 paper by Alan Guth</a> discussing eternal cosmic inflation, he start's using a value $\phi$ on page 8. My understanding is that $\phi$ is the scalar field representing the dark energy of a "false vacuum" - but then why does $\phi$ appear as th... | 2,498 |
<p>I have some question about interpreting PDG particle cross section data sets' metadata fields. The data sets I'm having questions for are <a href="http://pdg.lbl.gov/2011/hadronic-xsections/hadron.html" rel="nofollow">http://pdg.lbl.gov/2011/hadronic-xsections/hadron.html</a></p>
<p>For example, the data set for p-... | 2,499 |
<p>I'm trying to write N=4 SYM in terms of N=1 superfields. I have the lagrangian</p>
<p>$$\mathcal{L}=\frac{1}{16 k} \int d^2 \sigma \text{Tr} \big[W^a W_a\big]+c.c+\int d^4\theta \text{Tr}\big[\bar{\Phi}^i e^V \Phi^i e^{-V}\big]+\frac{\sqrt{2}}{3}\int d^2\theta \text{Tr}\big[\phi^i [\phi^j,\phi^k]\big]\epsilon_{ijk}... | 2,500 |
<p>Charged pions $\pi^\pm$ decay via an intermediate $W$ to (e.g.) a lepton-neutrino pair. </p>
<p>The pions being scalar (spin-0) particles and the intermediate $W$ having spin 1, how is spin conserved in this interaction?</p> | 2,501 |
<p>Are there any books or articles that describe models for transport in a metal/semiconductor junction where the thickness of the semiconductor is less than the thickness of the depletion/accumulation layer?</p> | 2,502 |
<p>Calculate $r$ vector and $v$ vector in AU and AU/TU respectively for the Halley's comet on September 12, 2014 given:
= 17.9 AU
= 0.967
= 2.8274 rad
Ω = 1.0210 rad
= 1.9513 rad
= 0 rad on February 9, 1986</p> | 2,503 |
<p>In relation to my question <a href="http://biology.stackexchange.com/questions/10945/isotropicity-of-sarcomere-bands-in-skeletal-muscle-cells">here</a> I wanted to make sure that my physical argument was not flawed. </p>
<p>Anisotropic properties, (especially refractive index) is characteristic of a well-ordered s... | 2,504 |
<p>What is the transfer matrix size for a strip lattice of width $n$ vertices, with arbitrary $q$??<br>
I am not sure if it is $q^n$ x $q^n$ or something else.</p>
<p>Any reference is also welcome.</p> | 2,505 |
<p>My textbook says talking about Cygnus X-1 (the first black hole to be identified as such) has variations in brightens of the order of 0.01 seconds and that this means that it's dimeter must be on the order of 3000km (=speed of light times 0.01). Why must this be so? The reason I asked is could (if it was not a black... | 2,506 |
<p><strong>Context</strong>: Solid state physics. Monoatomic linear chain.</p>
<p><strong>Question</strong>: To prove that the total momentum of the chain is zero.</p>
<p><strong>Attempted solution</strong>: I consider the sum:</p>
<p>\begin{align*}
p = \sum_{n=1}^{N} m \dot{u_n}
\end{align*}</p>
<p>where $u_n$ is ... | 2,507 |
<p>In the solution of Schrödinger Equation for harmonic oscillator why the distance between peaks of the probability distribution function decreases when n increases?</p>
<p>Is there a good reason for it or is it just the consequence of solving the Schrödinger Equation?</p> | 2,508 |
<p>Given complete knowledge of the precise state of every property of every particle and energy phenomenon existing in our universe for a given infinitely small frame of time, is it possible to completely determine the status of every property of every particle and energy phenomenon existing in the succeeding time fram... | 49 |
<p>If right in the centre of the Earth would be like a hole and I could teleport right there, what would happen to me? Would I explode, implode? My own theory is that maybe I would levitate because since I'm right in the middle, the gravity wouldn't affect me...</p>
<p>What do you guys think? </p> | 50 |
<p>I am appreciating particle physics and I read about mesons. In quark's model, mesons are pairs of quark-antiquark. Now I think that in general matter-antimatter annihilate and so I don't understand how meson could be possible. Why don't a couple up-antiup annihilates? </p>
<p>Thank you!</p> | 2,509 |
<p>Linear antenna directed along z, photons (EM waves) propagate along x. Momentum of photons have only x component. Why electrons in antenna have z component of momentum?</p> | 2,510 |
<p>The rate at which time passes is relative depending on speed and the gravity as predicted in general relativity. This theory has been tested by scientists by comparing two identical atomic clocks, one on Earth the other on a rocket speeding at escape velocity. The initially synchronised clocks measured different amo... | 2,511 |
<p>I'm working on a research project involving absorption spectra of particulates in solution. I was curious if someone could clarify or direct me to a resource that explains broadening mechanisms <em>specifically</em> for absorption spectra. For example, the oft-cited Heisenberg and Doppler broadening effects both mak... | 2,512 |
<p>When a light beam reaches a dielectric surface, the incident and reflected beams have different intensities depending on polarization. For the so-called Brewster's angle, the reflected light is lineary polarized.</p>
<p>My question is: how does this law work in case of mirror-like surface, when (ideally) all the li... | 2,513 |
<p>The question reads as such: "What is the mass of a 1.05 µCi carbon-14 source?"</p>
<p>First I convert to decays/s: $R = 1.05 µCi=3.885 \times 10^4 decays/s$.</p>
<p>The half-life for carbon-14 that we've been using is 5730 years or $T_{1/2}=1.808 \times 10^{11} s$, so $\lambda=\frac{ln(2)}{T_{1/2}}=3.834 \times 10... | 2,514 |
<p>The magnetic monopoles does not exist which can be shown by $ \int {\vec{B} \cdot d\vec{A}} = 0 $.</p>
<p>But in Faraday's Law of electromagnetic induction, we clearly show the EMF induced is the <em>time rate of change of the magnetic flux</em>, which is $ E = -\frac{d\Phi_B}{dt} = -\frac{d\int{\vec{B}\cdot d\vec... | 2,515 |
<p>The energy of a single planet in a gravitational potential is $$E=\frac{m\dot{r}^2}{2}+\frac{L^2}{2mr^2}-\frac{GMm}{r}$$
And the effective potential energy is defined as the last two terms. Note this satisfies $$F=-\nabla U$$
$$mr^2 \dot{\theta}-\frac{MmG}{r^2}=-\frac{d}{dr}(\frac{L^2}{2mr^2}-\frac{GMm}{r})$$
$$=\fr... | 2,516 |
<p>I have the following question to answer:
a force of160 N stretches a spring 0.050m from its equilibrium position.
A. what is the spring constant of the spring?</p>
<p>The equation for Hooke's Law in my text is F=-kx, where k is the spring constant. So with some simple algebra we can find an equation for k: k = -(f... | 2,517 |
<p>A proton p collides with a neutron(at rest) n at relatively low-energies and creates a 'deuterium-core' d:</p>
<p>$$p+n->d+\gamma$$</p>
<p>Find the wavelength for the photon as a function of the proton's momentum and the angle that the photon creates with the proton.Do this relativistic.</p>
<hr>
<p>So seems ... | 2,518 |
<p>In Misner, Thorne, Wheeler (henceforth written as "MTW"), "Gravitation", Box 16.4, there's an experimental setup construction (or method) presented by which</p>
<blockquote>
<p>"<i>Each geodesic clock is constructed and calibrated as follows: [...]</i>", where "<i>Those that pass through [event] $\mathcal A$ are ... | 2,519 |
<p>I'm well aware of transmutation as a way to effectively make radioactive material decay faster, however that isn't really what I mean.</p>
<p>Doing a quick Google search I found references to several theoretical treatises on the subject, and a few references to experiments with, at best, inconclusive results. Among... | 2,520 |
<p>I have read that quantum mechanics says that the amount of possible particle configurations is $10^{10^{122}}$ to be exact in the universe. Do we know this figure to be exactly true to the exact figure? Wouldn't we need to know a true theory of quantum gravity to know the exact answer? Is the amount exactly that fig... | 2,521 |
<p>My dad and I have tried to calculate the strength of the explosion if the lid was suddenly freed. We took some measures:</p>
<ul>
<li>Lid mass: $0.7 \textrm{kg}$</li>
<li>Lid surface: $0.415 \textrm{m}^2$</li>
<li>Internal pressure (above external): $ 1\textrm{atm}\approx 100 \textrm{kPa} $</li>
</ul>
<p>Now we ar... | 2,522 |
<p>I'm trying to find the electric field due to an electric dipole $\mathbf{d}$. There are plenty of approaches to doing this online, but I want to do it "my way," which doesn't seem to be working (and I have yet to find this approach in textbooks/online). I start with the potential:</p>
<p>$$ \phi(\mathbf{r}) = \frac... | 2,523 |
<p>So, let's say we have a spacecraft in deep space. It activates its rocket engines, to keep it simple. The engine reaction channels exhaust through the aft nozzle, right? How does that chemical reaction actually induce a change in the velocity of the spacecraft? The particles <em>have</em> to push against the geometr... | 2,524 |
<p>I accept the Big Bang theory. What I can't understand is how there can be a where or when to the Big Bang if space time did not exist prior to it. Did space and time exist prior to the Big Bang? </p> | 51 |
<p>How strong would have to be nuclear explosion on exo-planet that orbits some other star for it to be detectable outside of that system.<br>
Or it would be impossible due to amount <a href="http://www.neatorama.com/2008/03/22/trivia-solar-energy-1-trillion-1-megaton-atom-bombs-per-second/#!8m5ue" rel="nofollow">of ra... | 2,525 |
<p>I am presently in my senior year and I am considering fluid mechanics for my thesis.
What area of research of fluid mechanics which is purely analytical and very mathematical since I am an applied mathematician can I look into.
NOTE 1: I am from a 3rd world country and the academic standard is low.
NOTE 2: Please pr... | 2,526 |
<p>Here is a drawing of the circuit that is confusing me:
<img src="http://i.stack.imgur.com/Kag3r.png" alt="enter image description here"></p>
<p>I don't quite understand how batteries work in this diagram. If a battery has a negative and positive terminal, there must be a barrier preventing them from neutralizing on... | 2,527 |
<p>This is about a step in a derivation of the expression for the relativistic Doppler effect.</p>
<p>Consider a source receding from an observer at a velocity $v$ along the line joining the two. Light is emitted at frequency $f_s$ and wavelength $\lambda_s$. The frequency $f_0$ and wavelength $\lambda_0$ received by ... | 2,528 |
<p>I am reading Wald for the interior solutions of a static spherical metric. Assume it to be of the form
$$ds^2 = -f(r)dt^2 + h(r)dr^2 + r^2 ( d{\theta^2} \sin^2{\theta}d{\phi^2})$$</p>
<p>Wald states: For a perfect fluid tensor $T_{ab}= \rho u_a u_b + P ( g_{ab}+ u_{ab})$</p>
<blockquote>
<p>In order to be compa... | 2,529 |
<p>I'm reading the QFT textbook by Weinberg. In volume one chapter 10 page 451, at the lower part of the page he says,</p>
<blockquote>
<p>Now, because $\Pi^*_{\mu\nu}(q)$ receives contributions only from one-photon-irreducible graphs, it is expected not to have any pole at $q^2=0$.</p>
</blockquote>
<p>$\Pi^*_{\mu... | 2,530 |
<p>A cylinder of mass M and radius R is in static equilibrium as shown in the diagram. The cylinder
rests on an inclined plane making an angle with the horizontal and is held by a horizontal string
attached to the top of the cylinder and to the inclined plane. There is friction between the cylinder
and the plane. What... | 2,531 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.