question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I am considering a perturbation theory problem in quantum mechanics. The unperturbed hamiltonian is $$H_0 = A_1 \boldsymbol{B} S_{1z} + A_2 \boldsymbol{B} S_{2z}.$$</p>
<p>The eigenstates of the unperturbed hamiltonien are $ \mid M_1 M_2 \rangle$, where $-S_{1,2} \leq M_{1,2} \leq S_{1,2}$ ($S$'s are spin operators... | g17034 | [
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<p>I am trying to find a list with super conductors. In particular I am searching for a superconductor, that consists of 4 elements none of which is Oxygen.</p>
<p>The reason I rejected Oxygen, is because(from the kinematic factor) the maximum energy from scattering with the Oxygen is about $730 keV$.</p>
<p>Therefor... | g17035 | [
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<p>As I understand, the visible light from an optical telescope is focused on a sensor which correlates light exposure to an electrical voltage, which is then converted to an image.</p>
<p>A single antenna radio telescope's signal is focused on some sort a sensor but this signal represents only a single 'pixel.' To ge... | g17036 | [
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<p>$P=IV$, $P=I^2R$, $P=\frac{V^2}{R}$, what are the distinctions between these equations? How do you know which equation to use when?</p> | g516 | [
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<p>The Moon and Earth are approximately spherical conductive balls and the Earth has a self-capacitance of around 710uF. Is there ever a significant potential difference in the Earth-Moon system? Is there even a way to tell if there is? Presumably the Apollo astronauts didn't expect to be electrocuted on landing.</p>
... | g17037 | [
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<p>Why are all the interactions particle of a gauge theory bosons.
Are fermionic gauge particle fields somehow forbidden by the theory ?</p> | g17038 | [
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<p>We know due to <a href="http://en.wikipedia.org/wiki/Maxwell%27s_equations">Maxwell's equations</a> that: </p>
<p>$$\vec{\nabla} \cdot \vec{B}=0$$</p>
<p>But if we get far from the magnetic field, shouldn't it be weaker?
Shouldn't the divergence of the field be positive?</p>
<p>If we define the vector field as a ... | g17039 | [
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<p>Why is the speed of sound given so much importance in Astrophysics? For example in gas outflow (and accretion) problems, we often calculate the sonic point (the point at which the outflow speed becomes equal to the speed of sound). Is it simply because speed of sound is a convenient number that can be used to scale ... | g17040 | [
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<p>What does the plot of higgs branching ratio (see figure below) say about the higgs mass anyway? How can one use it as a guide to find the higgs mass experimentally? </p>
<p>If we e.g. go to $M_H=126$ GeV (in figure below) and then read off the different branching ratio: then if experiment agrees with this, it would... | g17041 | [
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<p>Is it possible, and has it been attempted, to use quantum mechanics to deduce Newtonian, macroscopic level mechanics laws as was the case of statistical mechanics deriving thermodynamic relations?</p> | g141 | [
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<p>I would like to know the physical meaning of the <a href="http://en.wikipedia.org/wiki/Legendre_transformation" rel="nofollow">Legendre transformation</a>, if there is any? I've used it in thermodynamics and classical mechanics and it seemed only a change of coordinates?</p> | g17042 | [
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<p>Audio is often explained by single frequencies. Typically <em>this is a sound wave</em>:</p>
<pre><code>plot sin(x) * 2 from 0 to 10
</code></pre>
<p><img src="http://i.stack.imgur.com/FzIdQ.gif" alt="plot sin(x) * 2 from 0 to 10"></p>
<p>However we usually deal with more complex sounds, more specific various fre... | g17043 | [
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<p>Let's consider five dimensional <a href="http://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory" rel="nofollow">KK theory</a>. This is Klein's metric</p>
<p>$\hat{g}_{AB}=
\begin{pmatrix}
g_{00}+A_{0}A_{0}&g_{01}+A_{0}A_{1}&g_{02}+A_{0}A_{2}&g_{03}+A_{0}A_{3}&A_ 0\\
g_{10}+A_{1}A_{0}&g_{11}+A_... | g17044 | [
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<p>Suppose I want to calculate the state associated with a spin particle under a magnetic field. I suppose the particle interacts via the Zeeman effect, and only through it. Then I want to resolve the Schrödinger equation: </p>
<p>$$\mathbf{i}\hbar\dfrac{\partial\Psi}{\partial t}+\dfrac{\hbar^{2}}{2m}\dfrac{\partial^{... | g17045 | [
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<ul>
<li><p>Can anyone tell me where can I read about the notion of "short" and "long" representations? Like what they are etc. </p></li>
<li><p>From where can I learn the arguments which show that the bosonic subalgebra of $\cal{N}=2$ and $\cal{N}=3$ Lie superalgebra are given by $SO(3,2)\times SO(2)$ and $SO(3,2)\tim... | g17046 | [
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<p>I find myself greatly fascinated by physics and astronomy, though I really do not understand most of it. For example, I avidly watch programs and read books that discuss our current search for a Unified Theory which will unite the major forces (Strong Interactive, Weak Interactive, Electromagnetism on the one side, ... | g17047 | [
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<p>Now that an equivalence of <a href="http://arxiv.org/PS_cache/arxiv/pdf/1101/1101.2451v2.pdf" rel="nofollow">Navier Stokes and Einstein</a> equations has been established, and it is known solutions to <a href="http://projecteuclid.org/DPubS/Repository/1.0/Disseminate?view=body&id=pdf_1&handle=euclid.cmp/1103... | g17048 | [
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<p>A barrel/drum with a diameter of 60cm is rotating at 20RPM to get a good mixing of the fluid contained (type thick oil). </p>
<p>At what RPM should a barrel of 30cm rotate to get the same mixing efficiency with the same fluid? To get the same peripheral velocity, the RPM should be 40RPM, but will this give the same... | g17049 | [
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<p>If you are in a perfectly circular orbit and accelerate perpendicular to your velocity (directly towards the center of the orbit), what would happen to your orbit? Would it just shift in the direction of acceleration?</p>
<p>Is there a different result if the orbit is not perfectly round?</p>
<p>The basis for this... | g17050 | [
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<p>I am studying the derivation of the black hole temperature by means of the Euclidean approach, i.e. by Wick rotating, compactifying the Euclidean time and identifying the period with the inverse temperature. </p>
<p>Consider the Schwarzschild case as an example. The Euclidean Schwarzschild metric is of course</p>
... | g17051 | [
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<p>I'm trying to understand the <a href="http://en.wikipedia.org/wiki/Quantum_pseudo-telepathy" rel="nofollow">wikipedia article on quantum pseudotelepathy</a>. I've been trying to figure out the quantum circuits the players can use to win the game from the wiki article.</p>
<p>(Level of knowledge: Everything I know a... | g17052 | [
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<p>Many (all?) materials are polarizable at some level; meaning that when we apply an electric field across the material, there is an induced dipole moment
$$
\vec{p}=\alpha(\omega)\vec{E},
$$
where $\alpha(\omega)$ is the polarizability of the material at frequency $\omega$, $\vec{E}$ is the applied electric field, an... | g17053 | [
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<p>From the quantum mechanics(QM) viewpoint, does there exist a Hamiltonian $H$ for the system of H$_2$O molecules? Assume that the number of H$_2$O molecules is fixed.</p>
<p>Imagine that by calculating the free energy $F(T)$ from the Hamiltonian $H$, one can reproduce the three common phases <strong>ice</strong>, <s... | g17054 | [
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<p>I have noticed that some people will say that, when you put more mass in an oven, it takes longer for both to cook than if just were one.</p>
<p>Some others will say that timings are the same. Assume we have an oven that's heated to 350 degrees fahrenheit, and it's 10 cubic feet(it should hold about 340 liters of l... | g17055 | [
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<p>Suppose a wheel with radius $R$ is resting on a non-inclined surface. A torque $\tau$ is applied to the wheel center. In an attempt to prevent wheel from spinning, the ground applies a static friction force to the wheel at the contact point (parallel to the surface), then the wheel starts rolling without spinning. T... | g17056 | [
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<p>As far as I know clouds are lot of small droplets condensed in air.</p>
<p>If droplets are large enough we see a rainbow. If they are small we see a <a href="http://upload.wikimedia.org/wikipedia/commons/a/ac/360_degrees_fogbow.jpg" rel="nofollow">fogbow</a>.</p>
<p>Although the size of the droplets are big enough... | g17057 | [
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<p>Here's another question concerning the Lindhard function as used in the physical description of metals. </p>
<p>First we define the general Lindhard function in the Random Phase approximation as
$\chi(q,\omega)=\frac{\chi_{0}}{1-\frac{4\pi e^2}{q^2}\chi_{0}}$ where $\chi_{0}$ denotes the "bare" Lindhard function" e... | g17058 | [
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<p>Cryogenics is related to very low temperatures, so, what is the term when referring to very high temperatures?</p> | g17059 | [
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<p>I'm a mathematics student with not much background in physics. I'm interested in learning about the path integral formulation of quantum mechanics. Can anyone suggest me some books on this topic with minimum prerequisite in physics?</p> | g981 | [
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<p>I'm trying to solve the following problem :</p>
<blockquote>
<p>An electron-positron pair annihilates, creating two photons. At what speed must an observer move along the line of the photons in order that the wavelength of one photon be twice that of the other?</p>
</blockquote>
<p>So far, I've found using $E=m_... | g17060 | [
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<p>I am trying to compile a list of fundamental commutation relations involving position, linear momentum, total angular momentum, orbital angular momentum, and spin angular momentum. Here is what I have so far:</p>
<p>$$
[x_i,x_j]=0 \\ [p_i,p_j]=0 \\ [x_i,p_j]=i\hbar\delta_{ij} \\ [J_i,J_j]=i\hbar\epsilon_{ijk}J_k \\... | g17061 | [
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0.008664963766932487,
-0.04316117614507675,
-0.06234389543533325,
-0.00874475110322237,
-... |
<p>I have been going through several calculations where I am asked to calculate $\langle p^2 \rangle$ and the task is proving to be pretty tedious. Does anyone know of a shortcut for this? Such as with $\langle p \rangle$ where:</p>
<p>$$ \langle p \rangle = m\frac{d\langle x\rangle}{dt} $$</p>
<p>I have seen a few... | g17062 | [
0.004483590833842754,
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0.05936087295413017,
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... |
<p>Google found these lyrics:</p>
<pre><code>I love the morn, to see the first Radon,
When the stars Argon,
As the night Krypton,
And, if it’s cloudy, you won’t Xenon.
</code></pre>
<p>Years ago, I saw approximately the same lyrics with sheet music. The staffs of the music turned into Feynman diagrams. I can't reme... | g17063 | [
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0.0051763323135674,
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<p>Qualitatively, for a plum pudding model atom (where the positive charge of each atom is even diffused throughout the volume of the atom) I think that the deflection of incident alpha particles would be caused by the electrons and not the positive charge at all. Is this correct?</p>
<p>Quantitatively, for a detecto... | g17064 | [
0.026473358273506165,
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0.010876511223614216,
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<p>Obviously experiment is the end-all-be-all of any science, but I'm curious if there's any a priori reason to model space as Euclidean three-space (from a pre-relativity viewpoint, of course; I'm ignoring the fact that space is only locally Euclidean). I'm comfortable with differential geometry if it's necessary.</p> | g17065 | [
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<p>$$\ddot\phi + \frac bm\dot\phi = \frac{F}{mr}$$</p>
<p>I want to integrate this to get an equation for $\dot\phi(t)$ but I don't know how to integrate double derivatives. The answers say that the homogeneous equation associated with it is:</p>
<p>$$\ddot\phi + \frac bm\dot\phi = 0$$
and by integrating that you get... | g17066 | [
0.03283317759633064,
0.03070680983364582,
0.01431398093700409,
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0.1010374054312706,
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0.04151328280568123,
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0.023039... |
<p>Can two particles remain entangled even if one is past the event horizon of a black hole? If both particles are in the black hole?</p>
<p>What changes occur when the particle(s) crosses(cross) the event horizon?</p>
<p>I have basic Physics knowledge, so I request that answers not assume an in-depth understanding o... | g17067 | [
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0.014595447108149529,
0.015430748462677002,
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0.018016507849097252,
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<p>Does corrosion of a sample of iron increases or decreases its mass? I think that the mass will increase because of additional oxygen atoms.</p> | g17068 | [
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<p>A near-sighted person without eye-glasses can not clearly see things at distance.</p>
<p>If he takes a photo of the things at distance, he can see the things from the photo much clearer, because he can place the photo much closer to his eyes.</p>
<p>If he turns his back at the things at distance, and holds a mirro... | g17069 | [
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<p>I am a first year physics student, but I am 20 years old (pretty old for my country, average starting age is 18), because I started after leaving med school, which I find extremely jailed in "memorization walls", with no place for analytical problem solving, something that I have loved all my life. I started to love... | g517 | [
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0.0... |
<p>You can't go faster than light, and light can't be additive (if you shine a light from a spaceship, the light is not going $c$+"speed of spaceship", it's just going like it always does).</p>
<p>But what happens when two spaceships, each going 75% the speed of light, are traveling directly towards each other?</p>
... | g109 | [
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<p>There are a number of questions on this site that explain the many wave-like behaviors of photons by making reference to <a href="http://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality" rel="nofollow">wave-particle duality</a>. </p>
<p>However, I have just finished reading Feynman's book <em>QED</em>, where he ... | g17070 | [
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<p>What is the relationship between <a href="http://en.wikipedia.org/wiki/Aharonov-Bohm_effect">Aharonov-Bohm effect</a> and Integer <a href="http://en.wikipedia.org/wiki/Quantum_Hall_effect">Quantum Hall effect</a>?</p> | g17071 | [
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<p>So I like to go outside for a morning coffee with a cigarette. In winter here it's usually between -5C to -25C, and sometimes it gets down to -30C and colder. Assuming that my coffee is about 75-80C, what are the chances that the coffee mug will shatter in the cold?</p>
<p>My mug is made from some kind of organic g... | g17072 | [
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<p><a href="http://www.digitaltrends.com/cool-tech/nasa-confirms-impossible-space-drive-actually-works-revolutionize-space-travel/" rel="nofollow">This article states</a>:</p>
<blockquote>
<p>But somehow, despite all of the reasons it shouldn’t work, it does.</p>
<p><a href="http://ntrs.nasa.gov/search.jsp?R=20... | g518 | [
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0.017846591770648956,
0.024898206815123558,
... |
<p>I'm working with a problem in linear elasticity, and I have to calculate the strain energy function as follows:</p>
<p>$$2W=σ_{ij}ε_{ij}$$</p>
<p>Where σ and ε are symmetric rank 2 tensors.</p>
<p>For cartesian coordinates it is really easy because the metric is just the identity matrix, hence:
$$
2W=σ_{xx}ε_{xx}... | g17073 | [
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0.04551727697253227,
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<p>1.) How do we physically interpret an active Lorentz transformation? The passive transformation seems simple enough: you view a fixed object from the perspective of a new observer. When we actively Lorentz transform a vector are we interpreting this as moving the vector to a new point in spacetime considered from th... | g17074 | [
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<p>I have this graph, and I need to know the <strong><em>displacement</em></strong> in the interval <strong>from 0 to 5 seconds</strong>, so I found the area of the rectangle that you can see there. A = w*h, which means X = (5 seconds)*(20 m/s), then <strong>displacement = 100 meters</strong>.<img src="http://i.stack.i... | g17075 | [
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<p>Is airplane moving slower at higher altitude ? If air is less compressed shouldn't propeller move less air ?</p> | g17076 | [
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<p>Recently I decided to brush on the those parts of classical mechanics that always gave me trouble. One of those parts was the <a href="http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation" rel="nofollow">rocket equation</a> so I figured that I would try to derive the appropriate equations from scratch. Evidently... | g17077 | [
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<p>Say you have two blocks with masses $m_1$ and $m_2$, where $m_1>m_2$. The smaller block sits atop the larger block. The larger block is connected to a spring, which is then connected to a wall a distance $x$ away. What must the coefficient of friction be in order for the smaller block to stay on top of the larger... | g17078 | [
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0.012105521745979786,
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<p>I would like to find the original reference in which the polar parameterization of quaternions was given (i.e. the relationship between the components of a unit quaternion and the polar angles of an axis and rotation angle of a three-dimensional rotation). I assume it would have been written by Hamilton, but the phy... | g17079 | [
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<p>Would it be possible to create shielding for a camera, allowing it record food being cooked from the vantage point of the inside of a consumer microwave oven without the camera being damaged?</p>
<p>Wikipedia says a consumer oven usually uses 2.45 gigahertz (GHz)—a wavelength of 12.2 centimetres. So surely you coul... | g17080 | [
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<p>The temperature of Hawking radiation is inversely proportional to the mass of a black hole, $T_{\rm H}\propto M_{\rm BH}^{-1}$, and so as the black hole shrinks the temperature of the radiation should grow. What happens as the mass shrinks to zero?</p>
<p>Naive application of the above formula leads to arbitrarily... | g17081 | [
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<p>OK - I have never posted on this site before, and I hope this question isn't closed as "request for reference" but here goes:</p>
<p>I'm a software guy who likes to dabble in math, physics and cosmology. Have read "The History of Time" and some books about information theory.</p>
<p>Last night, I started reading P... | g17082 | [
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<p>In flux compactifications to 4D, e.g. Type IIB on a CY orientifold $X$, one uses fluxes to stabilize the axio-dilaton $\tau$ and the complex structure moduli $z_a$ - the periods of the holomorphic three-form $\Omega$ over the basis three-cycles: $z_a=\int_{\alpha_a}\Omega$, by solving a system of equations for a sup... | g17083 | [
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0.054061... |
<p>This is a two-part question...</p>
<p>Firstly, models of the specific heat capacity $C$ (i.e. Debye, Einstein) in relation to the temperature $T$ give $C$ as steadily increasing with $T$. I assume that the change in $C$ is due to the heat the system gains being stored in its degrees of freedom- so why doesn't it in... | g17084 | [
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<p><strong>Update:</strong> I provided an answer of my own (reflecting the things I discovered since I asked the question). But there is still lot to be added. I'd love to hear about other people's opinions on the solutions and relations among them. In particular <strong>short, intuitive descriptions of the methods use... | g17085 | [
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<p>The electric power produced by a current $I\in\mathbb{R}^+$ and a voltage $V\in\mathbb{R}^+$ is
$$
P = IV.
$$
Now the current is given as an (alternating) current density $J(\mathbf{x},t)=\Im(e^{i\omega t} j(\mathbf{x}))$, $j:\Omega\to\mathbb{C}$, across the cross-section $\Omega\subset\mathbb{R}^2$ of a conductor. ... | g17086 | [
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<p>Recently I recorded UV-Vis spectra of liquids with a two-beam spectrometer (Perkin Elmer 900). Lack of proper racks for cells of 0.5 cm optical path length let me use a stack consisting of a 0.2 cm cell and a one of 0.5 cm. Such a stack was hold in both beams -- for convenience, the smaller ones filled with water,... | g17087 | [
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<p>Can anyone describe the mathematics behind the calculation of a <a href="http://en.wikipedia.org/wiki/Gravitational_keyhole" rel="nofollow">resonance keyhole</a> (for a two-body model)? It seems like the size and position of the keyhole should be a function only of mass and relative velocity, but I'm having difficu... | g17088 | [
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0.023713380098342896,
0.010405715554952621,
0.013568068854510784,
0.11525794118642807,
-0.041... |
<p>How radio waves create the current in antenna in terms of photons? If it is Compton scattering then why is not changed the freuency of photons?</p> | g17089 | [
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0.029252607375383377,
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0.02381792664527893,
-0.029574910178780556,
0.014187023974955082,
0.05337968096137047,
0.014934370294213295,
0.0081... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/7713/predicting-decay-rates-via-the-standard-model">Predicting Decay Rates via the Standard Model</a> </p>
</blockquote>
<p>More specifically, does (any) current theory allow for approximate or exact pre... | g519 | [
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<p>Let us consider a completely sealed weighing scale such that the air pressure above and below the pan of the scale are equal and is equal to 1 atm. pressure. The scale initially reads zero. Now if this weighing scale is placed in a completely evacuated chamber, will there be any change in the reading? I am guessing ... | g17090 | [
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<p>For <a href="http://en.wikipedia.org/wiki/Dispersion_relation" rel="nofollow">Dispersion relation</a> , according to Gaussian profile, the author in the <a href="http://arxiv.org/abs/0910.5922" rel="nofollow">equation 3 wrote as</a><br>
$\omega= \left(k^2+\omega_{mass}^2\right)^{1/2}$
My question is what is mass fr... | g17091 | [
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<p>I remember the following fact about a rigid pendulum:</p>
<p>The point when the pendulum weight is lowest is a stable equilibrium while the point where the pendulum weight is highest is an unstable one.</p>
<p>But if you perturb the suspension point of the pendulum with small, quick oscillations, the upper point b... | g17092 | [
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<p>How to prove that equivalent resistance of any passive network is always lower if we add a resistor between arbitrary two nodes?</p>
<p>Note that this is not necessarily a parallel circuit, 2 nodes that we connect with a resistor are not the same 2 nodes between we want to measure equivalent resistance but complete... | g17093 | [
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<p>Why we couldn't transmit Electricity wirelessly even after so many proposals available proposed by Tesla ?</p>
<blockquote>
<p>Tesla tried to generate more interest in Wardenclyffe by revealing its
ability to transmit wireless electricity, but Morgan was not
interested, and the 1903 "rich man's panic" on Wall... | g17094 | [
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<p>A common exercise in non-stationary electromagnetism is to find the electric and the magnetic field generated by a capacitor with round plates, if the potential difference between the plates varies in time (typically $V=V_0 sin( \omega t)$ or $V= \alpha t$).</p>
<p>While finding the fields internal to the capacitor... | g17095 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/1686/why-does-the-mass-of-an-object-increase-when-its-speed-approaches-that-of-light">Why does the mass of an object increase when its speed approaches that of light?</a> </p>
</blockquote>
<p>A charged ... | g54 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2229/if-photons-have-no-mass-how-can-they-have-momentum">If photons have no mass, how can they have momentum?</a> </p>
</blockquote>
<p>I'm sure this question has been asked here before but I wasn't able... | g195 | [
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<p>I'm a newbie here so have mercy. </p>
<p>I'm studying electromagnetic waves. This is the propagation of energy via the vibration of charged particles, as I understand it. </p>
<p>A charged particle could be like a proton, which has a positive charge. So I'm imagining a simplified "universe" that just exists along ... | g17096 | [
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<p>It is easy to understand the concepts of momentum and impulse. The formula $mv$ is simple, and easy to reason about. It has an obvious symmetry to it.</p>
<p>The same cannot be said for kinetic energy, work, and potential energy. I understand that a lightweight object moving at very high speed is going to do more d... | g17097 | [
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<p>I'm part of the Western Martial Arts/Historical European Martial Arts community, and a debate that often comes up is parrying with the edge vs parrying with the flat of a blade. I want to do some calculations myself to really convince myself one way or another.</p>
<p>Specifically what I'm looking to do is to calcu... | g17098 | [
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<p>How exactly was the <a href="http://en.wikipedia.org/wiki/Oh-My-God_particle" rel="nofollow">Oh-My-God particle</a> (ultra-high energy cosmic ray) observed and its energy measured?</p> | g17099 | [
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<p>I'm coding a basic simulation of using error correcting codes to transmit data from a satellite back to earth. I'm not sure what to set the "noise level" to. Let's say a satellite orbiting Mars transmits a signal which contains 128 bits, approximately how many of those bits would be changed by the time the signal re... | g17100 | [
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<p>A stone is dropped into a 40m deep well. The sound of the splash is heard 2.95 seconds after the stone is dropped. Find the speed of sound.</p> | g17101 | [
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<p>Let's suppose there is a very massive object and a small object that are 1 lightyear apart. </p>
<p>The massive object is large enough that the gravitational force pulling the small object is easily noticeable.</p>
<p>Suppose (never mind how) that through some freaky event the massive object suddenly disappears or... | g17102 | [
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<p>Well I'm learning about the models that have been proposed for the atom, and the Bohr model came up.
My teacher told me that the one of the main postulate of the theory is that when an atom is in ground state, it can neither absorb nor emit energy. This is what gives the atom its stability. However, it can obviousl... | g17103 | [
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<p>Below is the question from Andy Strominger's presentation at the String 2014 conference. The question was asked by credible physicist Ashoke Sen as an important question. </p>
<blockquote>
<p>"What is the precise relation between quantum entanglement and classical geometry?"</p>
</blockquote>
<p>Could somebody d... | g17104 | [
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<p>the spectrum of the Gamma and Alpha decays are both discrete, i.e. the $\alpha$-particles and the $\gamma$-rays take on only discrete values when emitted from a decaying nucleus.</p>
<p>Why is it then, that the $\beta^{\pm}$ can take on continuous values?</p>
<p>The main thing that distinguishes the beta decay fro... | g17105 | [
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<p>It is a classical theorem in quantum mechanics or quantum chemistry or quantum information that a two-fermion wave function has a beautiful canonical expansion:</p>
<p>$$f(x_1, x_2) = \sum_{j=1}^N \sqrt{p_j} \left( \phi_{2j-1}(x_1)\phi_{2j}(x_2) -\phi_{2j}(x_1)\phi_{2j-1}(x_2) \right).$$</p>
<p>Here $f$ is the wav... | g17106 | [
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<p>As per my knowledge, phase transformation require energy gain or loss.if we are changing a liquid to gas we heat it and that is how molecules of liquid gains energy and lattice spacing increases and bonds becomes weaker and thus gets converted to gas.
But we know that if we lower the pressure of water (a closed con... | g17107 | [
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<p>As I understand it, there is a large contingent of physicists who believe that the measurement problem is "solved" by decoherence, without, for example, needing to postulate the existence of "many worlds." Yet at the same time my understanding is that in the decoherence picture there is only unitary evolution of the... | g17108 | [
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<p><img src="http://i.stack.imgur.com/8m1Xj.png" alt="enter image description here"></p>
<ol>
<li><p>Consider the circuit shown, where $R_{1} > R_{2}$. I meant to say that resistance offered by the resistor 1 is greater than the resistance offered by the resistor 2. Keep $t$ constant i,e calculate the charge transf... | g520 | [
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<p>Suppose we have a cylindrical resistor, with resistance given by $R=\rho\cdot l/(\pi r^2)$</p>
<p>Let $d$ be the distance between two points in the interior of the resistor and let $r\gg d\gg l$.
Ie. it is approximately a 2D-surface (a rather thin disk).</p>
<p>What is the resistance between these two points?</p>... | g17109 | [
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0.02888374775648117,
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<p>How is the speed of light calculated? My knowledge of physics is limited to how much I studied till high school. One way that comes to my mind is: if we throw light from one point to another (of known distance) and measure the time taken, we could know the speed of light. but do we have such a precise time measuring... | g17110 | [
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<p>How to start with a perfect fluid concept and reach (by approximations through certain mathematically well defined assumptions) to the concept of particle ? Here newtonian gravitation is being assumed. The state equation of matter can be assumed to be that of dust.</p>
<p><strong>EDIT</strong></p>
<p>Assume any in... | g17111 | [
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<p>I know the basics of solar system like how Earth moves around Sun, and that we have so many planets, elliptical orbit of earth, and how far is sun from earth etc etc. I want to take a step back and understand how mankind has been able to construct this knowledge of solar system piece by piece. Questions:</p>
<p>-- ... | g17112 | [
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0.028143... |
<p>so I've been at this for about 3 - 4 hours now. It is an homework assignment (well part of a question which i've already completed). We did not learn this in class. All work is shown below. </p>
<blockquote>
<p>An atom in an excited state of $4.9 eV$ emits a photon and ends up in the ground state. The lifetime of... | g17113 | [
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<p>How has the distance between sun and earth been calculated by scientists?
and size of sun?</p>
<p>Thanks,</p> | g17114 | [
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... |
<p>When the 'photon' is emitted, it would reason that the result of the energy fluctuation that creates 'it' rather is created as an energy wave, which when measured by us or a surface, it 'becomes' as a particle.</p>
<p>If my reasoning is right, the question then becomes why, or how, this wave appears as a corpuscula... | g304 | [
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<p>So I'm reading my textbook and it says that that magnitude of air resistance $f(v)$ can be given as a taylor expansion:</p>
<p>$$f(v) = bv + c^2v = f_{\text{linear}} + f_{\text{quadratic}}$$</p>
<p>The linear term, $bv$ is related to the viscosity of the medium while the quadratic term is related to the density of... | g17115 | [
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0.00917873065918684,
0.01558984350413084,
-0.04571276530623436,
0.03424714505672455,
0.02... |
<p>How is it possible to discover neutrinos from the big bang? Were the neutrinos emitted just before the big bang? Or at the same moment? If they moved outward in all directions, basically unhindered by matter or gravity, how can we hope to ever detect them? Unless something caused some of them to turn back and tra... | g17116 | [
0.0010989605216309428,
-0.0013618760276585817,
0.03010725788772106,
0.01437887828797102,
0.022261401638388634,
0.016241157427430153,
0.005298559088259935,
0.04668815806508064,
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-0.08022420108318329,
-0.04488160461187363,
0.006199978291988373,
0.059285324066877365,
0.0... |
<p>Electrons naturally repel one another. However, in a superconductor, a phonon-mediated interaction causes the electrons to have a weak attractive interaction. Suppose that the interaction between two electrons is $V(\textbf{q})$ (the bare Coulomb interaction, which is $>0$) and that the effective interaction betw... | g17117 | [
0.06455274671316147,
0.05521982163190842,
0.007628691848367453,
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0.09312503039836884,
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0.013039479032158852,
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0.0826239362359047,
-0.030633054673671722,
0.00371... |
<p>I'm studying the Casimir Effect at finite temperature. To calculate the Helmoltz free energy in the canonical ensemble I need to sum a particular series. In some scientific papers it is suggested to use a modified Poisson formula over positive integers only that appears to be:</p>
<p>$$\frac{1}{2}F(0) + \sum_{n=1}^... | g17118 | [
0.00751966517418623,
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-0.01184901688247919,
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0.049909722059965134,
-0.022646687924861908,
... |
<p>String theory was originally formulated from a perturbative description (using quantum mechanics (QM) and replacing points by strings and evaluating path integral). Still, although QM has an upgrade to a field formalism -- QFT (that helps to solve the problem with causality and negative energy particles), I don't re... | g17119 | [
0.09541792422533035,
0.009241389110684395,
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0.03728271648287773,
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0.0093474630266428,
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-0.04434436932206154,
0.01787053607404232,
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0.0038074683398008347,
-0.022... |
<p>Does someone know some reference which treats QFT in a space with the following non-Lorentzian signature: $g_{\mu\nu}=\text{diag}(-1,-1,1,1)$. I'm interested in basic stuff like the shape of the scalar propagator and Feynman rules in such a space.</p> | g17120 | [
-0.049827393144369125,
0.007427000906318426,
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0.03188543766736984,
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0.03396029770374298,
0.00817192904651165,
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-0.012552439235150814,
-0.009826075285673141,
0.041191283613443375,
0.00614386610686779,
0.... |
<blockquote>
<p>Trolley with mass of $m_0=1 \ kg$ is moving without friction on the railway track. It is raining so there is a constant mass flow of water $\Phi_m=0.1\ kg/s$. Constant force $F=0.1 \ N$ is accelerating the trolly horizontally. </p>
<p>What is the velocity at time $t$ if the trolly is stationary i... | g17121 | [
0.03804420679807663,
0.017244616523385048,
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0.012506324797868729,
0.05313055217266083,
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0.07827876508235931,
0.006425901316106319,
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-0.021312829107046127,
-0.0373922698199749,
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0.054201796650886536,
-0.01... |
<p>Given a 2-state system with (complete set) orthonormal eigenstates $u_1, u_2$ with eigenvalues $E_1, E_2$ respectively, where $E_2>E_1$, and there exists a linear operator $\hat{L}$ with eigenvalues $\pm1$, </p>
<ol>
<li><p>would the normalized eigenfunctions (in terms of the given eigenstates) just be $$u_1\ove... | g17122 | [
0.004976494237780571,
-0.03626455366611481,
-0.0005240410682745278,
-0.016831928864121437,
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0.025321446359157562,
-0.003075715620070696,
0.020158881321549416,
-0.01488097757101059,
0.05526379495859146,
... |
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