question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I want to calculate the direction of the polarizing axis of a single polarizer.Is it possible to determine? If possible then How I can determine it?. </p> | g17481 | [
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<p>I am trying to understand electromagnetic fields so I have two question related to them.</p>
<ol>
<li><p>What is a electromagnetic field made of? Is it made of photons / virtual photons?</p></li>
<li><p>How about a static electric or magnetic field?</p></li>
</ol> | g558 | [
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<p>With laser scanning devices, very roughly speaking, the maximum deflection angle seems to be inversly proportional to speed. So for example, while acousto-optic deflectors can steer the beam very quickly, they can only do so over a small angle. As I understand it, this situation is roughly analogous to electrostatic... | g17482 | [
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<p>So the air pressure on earth remains relatively constant, right?</p>
<p><strong>Is there air gained or lost through transitions of any sort?</strong> e.g. plumes going out into space, earth gaining new air particles with gravity from air in the solar system.</p>
<p>I was curious to know whether in general the part... | g17483 | [
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<p><a href="http://en.wikipedia.org/wiki/Riemann_integral">Riemann integration</a> is fine for physics in general because the functions dealt with tend to be differentiable and well behaved. Despite this, it's possible that <a href="http://en.wikipedia.org/wiki/Lebesgue_integration">Lebesque integration</a> can be more... | g17484 | [
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<p>In string theory(s), are quarks just individual strings, or are they made of multiple strings? Are the heavier quarks made of heavier or longer strings? Are there red, blue, and green strings corresponding to the color charges of qcd? </p> | g17485 | [
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<p><a href="http://www.youtube.com/watch?v=SwFzn41DbEU" rel="nofollow">This is the wave by fans</a>. Does it satisfy the wave equation?</p> | g17486 | [
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<p><em>(this question is a crosspost from <a href="http://theoreticalphysics.stackexchange.com/questions/660/how-to-get-tangential-momentum-accomodation-coefficient-from-force-measurement-o">theoretical physics</a>.)</em></p>
<ul>
<li>I am using <a href="http://en.wikipedia.org/wiki/Atomic_force_microscopy" rel="nofol... | g638 | [
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<p>I'm attempting to solve the following problem:</p>
<p>Two friends hold on to a rope, one at each end, on a smooth, frictionless ice surface. They skate in a circle about an axis through the center of the rope and perpendicular to the ice. The mass of one friend is $a$ kg and the other has a mass of $b$ kg. The rope... | g17487 | [
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<p>Sorry if this question is dumb, and I know is physics 101, but I'm not that good with physics.</p>
<p>I'm writing an iPhone program that by collecting the acceleration data of the device tries to replicate the motion of the device in an virtual environment.</p>
<p>To simplify things, let's consider just one axis.<... | g17488 | [
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<p>So energy comes to earth from sun in the form of EM waves. Some of it is reflected back but some of it remains on earth and is used by plants to create food and some is used in the atmosphere creating storms. But how is <em>this</em> energy sent back to space?</p>
<p>If it is not sent back, then does it mean that t... | g17489 | [
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<p>Solitary waves are by definition a wave of single nature so the usual definition for periodic waves does not apply. <a href="http://www.coastal.udel.edu/faculty/rad/solcalc.html" rel="nofollow">R. Dalrymple</a> provides a definition but I saw a lot of other websites and papers which seem to use a wide range of defi... | g17490 | [
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<p>Follow up to</p>
<p><a href="http://physics.stackexchange.com/questions/168/intuitively-why-is-a-reversible-process-one-in-which-the-system-is-always-at-eq">Intuitively, why is a reversible process one in which the system is always at equilibrium?</a></p>
<p>and</p>
<p><a href="http://physics.stackexchange.com/qu... | g17491 | [
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<p>I'm trying to think of an intuitive reasoning for why $F^{\mu\nu}F_{\mu\nu}$ and $\tilde{F}_{\mu\nu}F^{\mu\nu}$ are Lorentz invariant. By this I mean that I don't simply want to show that they remain unchanged after actually performing a Lorentz transformation and seeing that I end up with the same expressions, but ... | g17492 | [
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<p>Is it possible that we have entanglement in different degrees of freedom of a singe particle.
like spin and linear momentum .</p> | g17493 | [
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<p>since we know that gravitational force is nothing but a curvature in space-time.
I have a similar analogous for the electric or magnetic charges. Similarity is that both electromagnetic and gravitational forces follow the inverse square law. consequence of this can be that we can have a another interpretation of ele... | g537 | [
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<p>I deal with complex phase equilibria involving solid and liquid phases at high temperature. Below is a simplified temperature-XH2O diagram for a multicomponent system at constant pressure. </p>
<p><img src="http://i.stack.imgur.com/eWKdY.png" alt="enter image description here"></p>
<p>(Note: The bottom axis repres... | g17494 | [
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<p>The way I've always thought about is something like this: If measurements of space and time are essentially indeterminate (indeterminacy principle), then an entity "traveling at less than the speed of light" can be measured by another entity as "traveling at greater than the speed of light". It can be shown that th... | g538 | [
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<p>Would anyone suggest me useful web resources on lie groups and lie algebra and a good book to start with?</p> | g177 | [
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<p>What is the difference between <a href="http://en.wikipedia.org/wiki/Dispersion_%28water_waves%29" rel="nofollow">dispersion</a> and <a href="http://en.wikipedia.org/wiki/Diffusion" rel="nofollow">diffusion</a>?
Currently I believe, that diffusion is the mixture of molecules due to Brownian motion. So I read everywh... | g17495 | [
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<p>On page 20 of <em>A Brief History of Time</em>:</p>
<blockquote>
<p>. . . all observers should measure the same speed of light, no matter
how fast they are moving.</p>
</blockquote>
<p>But in an observer's frame of reference, they're actually not moving at all. So the sentence "should" read, ". . . they are mo... | g17496 | [
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<p>I came across an article claiming that if you charge two plates, one positive and one negative, and fasten them together (assuming they are insulated from each other), they will float in the air. I kind of got the idea that it depends directly on the voltage and it seems to require at least a hundred thousand volts.... | g17497 | [
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<p><strong>The following are some assumptions I'm basing my question on</strong>, from what (little) I understand of physics. I list them so an expert can (kindly) tell me where I'm going wrong.</p>
<ul>
<li>There is a probability assigned to every possible sequence of events. </li>
<li>Besides sequences that violat... | g17498 | [
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<p>Let's have two orthogonal n-particle quantum states: $|\psi \rangle$ and $|\phi \rangle$. In theory it is always possible to make an unambiguous measurement.</p>
<p>However, things get complicated when one restricts oneself to a certain class of measurements. With so called LOCC (Local Operations and Classical Comm... | g17499 | [
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<p>Consider an elevator moving upward with constant velocity. The constant velocity is maintained by an upward tensional force equal to weight. If we add the total work done on the elevator it will be zero since work done by two equal and opposite forces cancel out. But the elevator's P.E is increasing. How and who doe... | g17500 | [
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<p>Lightning and thunder during a snow storm is uncommon. As far as I know, more uncommon than during a typical rain storm. Why is this? I speculate it might be one, or both, of the following two ideas, one having to do with a change in the dielectric, the other having to do with a change in the catalyst. </p> | g17501 | [
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<p>The <a href="http://en.wikipedia.org/wiki/Kruskal%E2%80%93Szekeres_coordinates" rel="nofollow">Kruskal-Szekeres solution</a> extends the exterior Schwarzschild solution <em>maximally</em>, so that every geodesic not contacting a curvature singularity can be extended arbitrarily far in either direction. </p>
<p>Wiki... | g17502 | [
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<p>Maybe it's my ignorance of astrophysics/cosmology, but I have been wondering this:</p>
<p>Why do galaxies not appear stretched when we observe them? Assuming a galaxy that we observe is 100,000 light years in diameter, and we are viewing at an angle that is almost sideways, but enough to see its shape, there would ... | g539 | [
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<p>Suppose you have some sort of a "black box" system - you know nothing of its inner workings. The system has two outputs, let's call them A and B, and it occasionally emits photons - one photon from each output, with both the A photon and B photon emitted simultaneously. You observe the system for a while, and notice... | g17503 | [
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<p>I know that there are many different types of ice and many ways for ice to form but I want to know about ice that a human might typically encounter, i.e. from a freezer or a sub-zero environment (frozen lake or river strong enough to walk on safely). How does it compare to other common household objects? For example... | g17504 | [
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<p>Is it possible to measure the plane spacing in a crystal by measuring the angle at which transmitted light intensity dips? </p> | g17505 | [
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<p>Is there a model of <em>modified gravity</em> that either was close to or have succeeded in modelling the problem of dark energy, and suffers from no instabilities and explains the observational data. Also has the approach to use modified gravity to explain the problem of dark energy been abandoned?</p>
<p>Needed t... | g17506 | [
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0.09013473242521286,
-0.04006662219762802,
0.04838765785098076,
-0.0... |
<blockquote>
<p>The formation of ice from water is accompanied by:</p>
<p>A. absorption of energy as heat </p>
<p>B. temperature increase</p>
<p>C. decrease in volume </p>
<p>D. an evolution of heat </p>
<p>E. temperature decrease</p>
</blockquote>
<p>For the first one I think it's correct b... | g17507 | [
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0.00784277729690075,
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0.017379157... |
<p>when comb is rubbed with hair, and brought near small pieces of papers, small paper pieces gets a towards comb. Here the comb gets negatively charged and when brought near piece of paper where do electrons go because after sometime attraction of paper pieces towards comb stops and comb doesnt have negative charge th... | g363 | [
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-0.0... |
<p>I was browsing Reddit and I stumbled upon <a href="https://www.youtube.com/watch?v=54R6q2_-4Yo" rel="nofollow">this</a>. It is a video on making duct tape glow a blue light by pulling two pieces of duct tape apart. Appearntly the glowing is caused by something called <a href="http://en.wikipedia.org/wiki/Tribolumine... | g540 | [
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<p>So I've seen different reasonings for this; which is correct, or are they both corollaries of each other?</p>
<p>1) For a particle to be at rest, we would know its momentum and therefore by Heisenberg's uncertainty principle, the uncertainty in its position would be infinite. Is this acceptable?</p>
<p>2) $\lambda... | g17508 | [
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-0.... |
<p>I've done experiments on the thermo-viscoelasticity of liver tissue and the following results</p>
<pre><code>temp shift
1 20 4
2 30 8
3 40 20
4 45 49
5 50 300
6 55 8000
7 60 60000
</code></pre>
<p><img src="http://file2.npage.de/013648/02/bilder/curved_loglog.jpg" alt="shift vs temp ... | g17509 | [
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0.00... |
<p>So I still not sure how to apply like Right-hand rule (RHR) in this setup in problem like the one in the following so I tried to do RHR in order to get the direction but it didn't work out. This is an example from the Halliday and Resnick book.</p>
<blockquote>
<p>Figure 32-24 shows a wire segment, placed in a un... | g17510 | [
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0.0... |
<p>I was recently playing with <a href="http://demonstrations.wolfram.com/BeatFrequencyOfSoundWaves/" rel="nofollow">this Wolfram Demonstrations applet</a>, which demonstrates beats. </p>
<p>At first I thought the app didn't work because I couldn't hear any beats. Then I realized that the applet doesn't analytically... | g17511 | [
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<h1>Background</h1>
<p>Trying to determine how much weight a post can support without <a href="http://en.wikipedia.org/wiki/Necking_%28engineering%29" rel="nofollow">necking</a> when a monitor is attached to an articulated arm: a <a href="http://www.efunda.com/formulae/solid_mechanics/beams/casestudy_display.cfm?case=... | g17512 | [
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<p>For a $c=1$ Boson on a circle at the self-dual rdius, we get an enhanced gauge symmetry $\hat{SU}(2)_1$. It is said that we can orbifold this model by any finite subgroup of $SU(2)$ since $SU(2)$ is a symmetry of the model. But the Lagrangian of a $c=1$ Boson does not have an $SU(2)$ symmetry even at the self-dual r... | g17513 | [
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0.04747067391872406,
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0.05746696889400482,
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... |
<p>Why is the following equation true?</p>
<p>$$\frac{\partial \mathbf{v}_i}{\partial \dot{q}_j} = \frac{\partial \mathbf{r}_i}{\partial q_j}$$</p>
<p>where $\mathbf{v}_i$ is velocity, $\mathbf{r}_i$ is the displacement, and $q_j$ is the generalized coordinate into which $\mathbf{r}_i$ is transformed.</p>
<p>In read... | g17514 | [
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-0.... |
<p>I'm convinced that water waves for example:</p>
<p><img src="http://i.stack.imgur.com/4eLQT.jpg" alt="Water wave jpg"></p>
<p>are a combination of longitudinal and transverse. Any references or proofs of this or otherwise?</p> | g17515 | [
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0.02... |
<p>I'm having some problems in understanding the principles of sound propagation. The wave propagates though air (for example) exerts compression, which is followed by rarefaction. I think I got than right.</p>
<p>This is what I don't understand: What happens with the particles when the energy passes? Do they oscillat... | g17516 | [
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0.0444... |
<p>Let's look at Wikipedia example of applying Shannon–Hartley theorem to an additive white Gaussian noise (AWGN) channel with B Hz bandwidth and signal-to-noise ratio S/N.</p>
<p>$$
C = B \log_2 \left( 1+\frac{S}{N} \right)\
$$</p>
<p>where C is the channel capability in bits/second, B is the bandwidth in Hz, and S... | g17517 | [
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0.005938485264778137,
0.... |
<blockquote>
<p>If the gravitational field vector is independent of the radial
distance within a sphere, find the function describing the mass
density $\rho (r)$ of the sphere.</p>
</blockquote>
<p>I uses the divergence of $\bf g$:</p>
<p>$$\begin{align}
\nabla \cdot\vec g &= 4\pi G\rho \\
g &= -GM\frac... | g17518 | [
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0.0022129181306809187,
0.037359971553087234,
-0.0... |
<p>I know that the rotation energy of a diatomic homonuclear molecule is $E_{Rot}=\frac{\hbar J(J+1)}{R^2 M}$. Does the axis of rotation depend on $J$? With respect to which axis does the molecule for $J=1$ and why is that so?</p> | g17519 | [
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<p>I've been thinking about how astronomers can look at bright dots in the sky and deduce a whole bunch of things from their movements. I'm particularly interested in how people like Kepler and Galileo, 400 years ago, were able to deduce that planets move in ellipses and work out laws like equal times means equal areas... | g17520 | [
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<p>I'm often looking for old physics papers that had a big impact on science (Nobel prize, for example). But I can't seem to find a lot of them. Is there a reason why some papers are not digitally available, but others (that had less impact) are?</p>
<p>Specifically, currently I'm looking for:</p>
<blockquote>
<p>W... | g17521 | [
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0.008738940581679344,
0.014611084014177322,
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0.02810320071876049,
-0.007427... |
<p>Forgive me if the answer to this is obvious. I have no formal physics training, and I remember that when I asked my physics teacher this, she just frowned and said "Good question."</p>
<p>An electron is negatively charged. A proton is positively charged. Based on basic principles, it seems like it would be logic... | g132 | [
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0.03408299386501312,
0.0... |
<p>Do Newtonian Physics help in determining the escape velocity at and inside the event horizon at a distance less than Schwarzchild Radius from the singularity?</p> | g17522 | [
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<p>I am sorry if this question is silly; it′s just one of those things I wished I asked before leaving university.</p>
<p>If there were a static universe only as big as the size of two particles, say electrons, and there were one electron in it going back and forth from point A to point B: would time also go back and ... | g17523 | [
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0.01617712527513504,
0.012... |
<p>At the atomic level, at sea level on earth, what percentage of normal pure drinking water is void or empty space? What percentage of lead (the kind used to insulate from nuclear radiation) is void or empty space?</p> | g17524 | [
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<p>Since thrusters have no matter to push off of, how can a spacecraft generate thrust in the vacuum of space?</p> | g17525 | [
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0.0440... |
<p><strong>Warning</strong>: by background is in math, not physics. I've just recently started working with things that are close to theoretical physics. So please note that</p>
<ol>
<li>I'm still very confused by the jargon.</li>
<li>Maybe I'm asking something trivial, in which case please just give me some reference... | g17526 | [
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0.0... |
<p>Just as we have an abstract state vector $|\psi\rangle$ and its position representation $\psi(\vec{x}) = \langle \vec{x} | \psi \rangle$, how do we transform between a linear operator, say $H$, that acts on state vectors thus: $H |\psi\rangle$, and the differential operator form of the Hamiltonian that can act on th... | g17527 | [
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0.007126316428184509,
0.04327770695090294,
0.03... |
<p>I was taught in school that acceleration due to gravity is constant. But recently, when I checked Physics textbook, I noted that</p>
<p>$$F = \dfrac{G \cdot m_1 \cdot m_2}{r^2} $$</p>
<p>So, as the body falls down, $r$ must be changing, so should acceleration due to gravity.</p> | g17528 | [
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0.018507452681660652,
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0.0078371008... |
<p>A <a href="http://en.wikipedia.org/wiki/Fluorescent_lamp" rel="nofollow">fluorescent tube</a> (home-based) works on the principle of discharge of electricity through gases, as far as I can tell (I don't know much about cathode rays or gas discharge)</p>
<p>What happens inside the tube to create this pink color? Wik... | g17529 | [
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0.... |
<ol>
<li><p>What is the relationship between the Schwarzschild radius and Black hole Singularity?</p></li>
<li><p>Can the Planck length be the length of singularity?</p></li>
<li><p>Or is the length of the Schwartzschild shorter than the Planck length?</p></li>
</ol> | g17530 | [
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0.03959998860955238,
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<p>Suppose you reset the parameters of the standard model so that the Higgs field average value is zero in the vacuum, what would happen to standard matter?</p>
<p>If the fundamental fermions go from a finite to a zero rest mass, I'm pretty sure that the electrons would fly away from nuclei at the speed of light, leav... | g571 | [
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... |
<p>It is rather obvious for me that the generalized optical theorem (see e.g. Peskin&Schroeder) must hold for S-matrix elements for fermions as it is directly related to the unitarity of the S-matrix. But what about the generalization by Cutkosky to individual Feynman graphs? Do Cutkosky rules hold for any Feynman ... | g17531 | [
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... |
<p>This question regards Ewings molecular theory of magnetism<br /><br />
I.) Ewing's molecular theory of magnetism describes every magnetic substance as being a collection of dipoles that are initially in a state where there is no specific and uniform orientation as a result of the application of a magnetic field and ... | g17532 | [
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<p>I'm trying to write a piece of code that calculates a diffraction pattern similar to an X-ray experiment using a FFT.</p>
<p>From my knowledge, the diffraction pattern for point particles can be calculated from the following formula:</p>
<p>$$
S(\mathbf{k}) = \left| \int_V d\mathbf{r}\rho(\mathbf{r})e^{-i\mathbf{k... | g17533 | [
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-0.02914242073893547,
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0.029081221669912338,
0.0036995538976043463,
-0.023787938058376312,
0.03380713611841202,
-0.04500642418861389,
-0.046618200838565826,
0.008163726888597012,
0.07056011259555817,
0.06965432316064835,
0.0... |
<p>I am trying to solve the following equation for a positively charged plane with charge density $\sigma$ at $z = 0$. </p>
<p>$$ \phi''(z)=-\frac{e}{\epsilon \epsilon_0} \big(z_+n_{+} e^{-\beta z_+ e\phi}-z_{-} n_{-} e^{\beta z_- e\phi} \big) $$</p>
<p>So far I have determined that the electric field and potential ... | g17534 | [
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0.02259601652622223,
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0.049... |
<p>I have digitized a video of a flying fly in a 3-dimensional space.</p>
<p>At all instants I know the x, y, and z co-oridinates of the following points on the fly's body ---</p>
<p><img src="http://i.stack.imgur.com/T3XGk.jpg" alt="enter image description here"></p>
<p>The points are my choice, and the points can ... | g17535 | [
0.037808604538440704,
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<p>When you send some kind of radio signals at some frequency say 5 GHz to a repeater and it transmits it back at higher power, what change is made to the radio signal? For example: Will it be transmitted back at higher frequency or in what terms it is said to be amplified? How do you measure its strength?</p> | g17536 | [
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<p>I am not sure which form of <a href="http://en.wikipedia.org/wiki/Maxwell%27s_equations">Maxwell's equations</a> is fundamental, integral form or differential form. Imagine an ideal infinitely long solenoid. When a current is changing in time, can we detect classical effects outside a solenoid, for example generatin... | g17537 | [
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<p>Neutrinos can't be given Dirac masses because there is no $SU(2)_L$ singlet right handed neutrinos in the standard model. But can neutrinos be given Majorana masses in the standard model?</p>
<p>EDIT: Why Majorana mass term cannot be included for neutrinos in the $SU(2)_L\times U(1)_Y$ standard model without any mo... | g17538 | [
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<p>I have been watching <a href="https://www.youtube.com/watch?v=Vv6Q_SW71zM" rel="nofollow">this video</a> carefully and I want to know how the wings of birds generate thrust. This is because the wings are more or less flapping up and down --- generating the lift. But I do not see any appreciable change in the angle o... | g17539 | [
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<p>I am confused with the <a href="http://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect" rel="nofollow">Bohm-Aharonov effect</a>: though quantum mechanics is said to be gauge invariant, the presence of a solenoid imposes a gauge. I used to think that a phase shift did not change anything in the physical interpreta... | g17540 | [
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<p>I have a circuit for which output current waveform has both positive and negative points. Now I want to get a center of the charge for this waveform (means where my net charge is concentrated ?). Is there any formula or theorem to calculate this.</p>
<p>My current waveform has time on $x$ axis and current values at... | g17541 | [
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<p>I know what a gaussian fixed point is, and I did read the <a href="http://en.wikipedia.org/wiki/Gaussian_fixed_point" rel="nofollow">wikipedia entry</a>, but it wasn't helpful. It says because the probability distribution is gaussian, but what probability distribution? </p> | g17542 | [
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<p>Suppose a wheel is rolling smoothly on a horizontal plane i.e., it is rolling without slipping.</p>
<p>Now let's take the two cases of the horizontal plane:</p>
<ol>
<li><p>It has friction</p></li>
<li><p>It is frictionless</p></li>
</ol>
<p>In the first case, as of my knowledge friction doesn't come into play wh... | g17543 | [
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<p>Just a quick sanity check here:</p>
<p>I'm preparing a tutorial for a class on classical electrodynamics and I wanted to show an example of a gauge condition which leads to a contradiction, so I simply thought of $$(A^\mu)' = A^\mu - \partial^\mu \chi \stackrel{!}{=} 0\quad \forall \mu \in \{0,1,2,3\}\qquad (1)$$
F... | g17544 | [
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<p>While playing with voltage multiplication and capacitors, I began to think if my experiments could damage my electrical equipment (eg. mobile phone) by creating strong magnetic fields over a short duration. (for example when experimenting with coil gun technology)</p>
<p>So far, I have restrained myself to human-sa... | g17545 | [
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<p>Other than notation devices, I don't see any direct application of matrices/determinants in physics. For example, they are just a different way to write a partial derivative and determinants find if they can be explicitly solved if written down as simultaneous equations. Calculus, for instance, can be directly appl... | g17546 | [
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<p>Azimuthal quantum number $l$, and magnetic quantum number $m$ are defined when we do derivation for $L^2f=l(l+1){\hbar}^2f$ and $L_zf=l{\hbar}f$. </p>
<p>This is my own conclusion after studying introduction to quantum mechanics by Griffiths. Correct?</p>
<p>But I don't know why does $L_zf=l{\hbar}f$ become $L_zf=... | g17547 | [
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<p>I have a real scalar field which is given by the propagator as:</p>
<p>$$[\phi(x),\phi(y) ] =\int \frac{d^3 p}{(2\pi)^3} \frac{1}{2E_0} (\exp(-ip\cdot (x-y)) -\exp (ip\cdot (x-y)))$$</p>
<p>And I am asked to show that this equals $$\frac{1}{4\pi r} \partial_r J_0(m\sqrt{t^2-r^2})$$</p>
<p>Where $J_0$ is bessel fu... | g17548 | [
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<p><a href="http://en.wikipedia.org/wiki/Gabriel_Kron" rel="nofollow">Gabriel Kron</a> was an important research electrical engineer known for applying differential geometry and algebraic topology to the study of electrical system.
Towards the end of his career he published a number of unusual, even by his standards, p... | g17549 | [
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<p>Suppose a large neutron star were to be spun-up by a particular pattern of mass-accretion. The increased centrifugal force could presumably mitigate the increased gravity thus delaying gravitational collapse. How far could this process be taken?</p> | g17550 | [
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<p>I watched a short introduction video online. There are few concepts which are a bit confusing. </p>
<p>1) The video said the laser is single mode (monochromatic), the wavelength is 780nm, so what is that wavelength really refer to? What I am asking is what's the wavelength related to the medium creating that laser?... | g17551 | [
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<p>I went to a grocery store on a hot day that was very well air-conditioned, and I noticed as I went through the open entrance that there seemed to be a very powerful downward air current right at the doorway. After crossing the invisible threshold, the temperature immediately dropped a good 15 degrees or so.</p>
<p... | g17552 | [
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<p>just wondering if it is a distinction without a difference - it seeming a bit weird that one thing can decay into different things.</p> | g17553 | [
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<p>How does one calculate the gravitational field of an irregularly shaped object? I was thinking specifically of the gravitational field due to a human, and tried to see if modeling a human as an infinite wire would work, and of course it's a horrible approximation*. </p>
<p>Is there anyway to do it without relying o... | g17554 | [
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<p>Basically in almost every semiconductor texts, there will be all these concepts concerning electrons, holes, dopants, fermi-levels.</p>
<p>However, I have been always confused about the picture of hole transport in semiconductor device, say, a simple PN junction.</p>
<p>With a specific acceptor level and dopant co... | g17555 | [
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<p>Let's have metrics
$$
ds^{2} = f(\mathbf r)dt^{2} - h(\mathbf r )\delta_{ij}dx^{i}dx^{j}.
$$
Hot to show that motion of light in spacetime with this metrics is equal to motion in continuous media with refractive index $n = \sqrt{\frac{h}{f}}$?</p>
<p>Is it logical to start from Maxwell equations in curved spacetime... | g17556 | [
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<p>In a recent spectroscopy lab I performed for one of my classes we used a Lambda Scientific LLE-1/2 mercury/sodium lamp (to look at the sodium doublet) and a Lambda Scientific LLE-8 hydrogen/deuterium lamp (to look at the hydrogen/deuterium line). I have been trying to find exactly how these lamps excite the atoms in... | g17557 | [
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<p>In 1+1D Ising model with a transverse field defined by the Hamiltonian
\begin{equation}
H(J,h)=-J\sum_i\sigma^z_i\sigma_{i+1}^z-h\sum_i\sigma_i^x
\end{equation}
There is a duality transformation which defines new Pauli operators $\mu^x_i$ and $\mu^z_i$ in a dual lattice
\begin{equation}
\mu_i^z=\prod_{j\leq i}\sigma... | g17558 | [
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<p>I am 16 at the moment. I am really interested in physics. Especially particle physics. Can someone please tell me how to start learning the subject. like what to learn first. like which fundamental theories and concepts, the math needed in it, etc, etc.</p> | g17559 | [
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<p>If the Hamiltonian has basis of eigenvectors $\phi _1, \phi_2,..$ with corresponding eigenvalues $E_1,E_2,...$.</p>
<p>I then define an observable $A$ by:</p>
<p>$$A\phi_1 = \cos(\beta)\phi_1 + \sin(\beta)\phi_2$$
$$A\phi_2 = \sin(\beta)\phi_1 -\cos(\beta)\phi_2$$
And $A\phi_n=0$ for all $n=3,4...$</p>
<p>Now I c... | g17560 | [
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<p>What is the motivation for the definition of concurrence in quantum information? On the surface, the definition looks pretty ad hoc.</p>
<p>The definition is often given for the case of 2 qubits only. What is the generalization to higher dimensional spaces?</p> | g17561 | [
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<p>How does a fan moves air towards you (I mean in 1 direction). Also propeller and fan have different shapes, does it mean they work different?</p> | g541 | [
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<p>I'm working on a drone simulator to make the physics classes more interesting for the students, especially for ones do not like this subject so much.</p>
<p>What kind of information can help the teachers in their classes?</p>
<p>If you are a teacher, I will appreciate so much your contribution</p>
<p>Thank you</p... | g17562 | [
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<p>LO-TO splitting occurs in an <em>ionic</em> (i.e. polar) solid such as GaAs or NaCl. What happens is that the degeneracy of the transverse optical (TO) and longitudinal optical (LO) phonons at $k=0$ is broken and the LO phonon has a greater energy. From a physical point of view, in the limit that the wavelength is i... | g17563 | [
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<p>I'm in a first year statics course. We have spent the whole semester solving for forces and moments so that the system is in equilibrium.</p>
<p>When we are given a system, we immediately begin solving for all variables for the system to be in equilibrium. But how do we know that the system <em>can</em> be put in e... | g17564 | [
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<p>Consider a Dp-brane. Compactify $d$ spatial dimensions over a torus $T^d$. Suppose $d\geqslant p$, and that the Dp-brane is completely wrapped around the compactified dimensions.</p>
<p>Look at the open string modes ending on this wrapped D-brane. There is a zero energy open string mode associated with each spatial... | g17565 | [
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<p>The question <a href="http://physics.stackexchange.com/q/41392">Statistics of bound states of anyons with order pq</a>, and its answer inspires this question.</p>
<p>Suppose you have an anyonic particle with nonintegral spin s. Presumably, if there's an (unstable) bound state between this anyon and its antianyonic ... | g17566 | [
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<p>We found VY Canis Majoris, a star so big it can't even be seen in scaled illustratations with the sun itself.</p>
<p>However, we stop at particle physics, or quantum mechanics, i.e. particles, subatomic, etc.</p>
<p>If stars keep getting bigger, and we keep finding things bigger, and the size of the universe still... | g17567 | [
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<p>I have demonstrated that <a href="http://en.wikipedia.org/wiki/Weight" rel="nofollow">weight</a> only is measured based on the gravitational pull of where you live.</p>
<p>For example, the gravity on the surface of Mars is three times smaller than the gravity on the surface of Earth.</p>
<p>So my question is simpl... | g17568 | [
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<p>In <a href="http://www.goodreads.com/book/show/1258635" rel="nofollow"><em>The Variational Principles of Mechanics</em></a> by Lanczos, in section 1 of Chapter 1, Lanczos states that for a complicated situation, the Newtonian approach fails to give a unique answer to the problem, in contrast to the analytical mechan... | g17569 | [
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