question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I have chosen to make my own solar filter using Baader as opposed to Mylar or anything else based on these: <a href="http://physics.stackexchange.com/a/25204/6805">http://physics.stackexchange.com/a/25204/6805</a> and <a href="http://irwincur.tripod.com/mylar_vs__baader.htm" rel="nofollow">http://irwincur.tripod.com... | g14072 | [
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<p>A Lightning rod is fixed to the building and it is not given earthing then what happens? How does the lightning reach the ground through the building?</p> | g14073 | [
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<p>I'm trying to understand the constraints on the disk CFT correlation function $\langle O_1(y_1)O_2(y_2)\rangle$, where the $O_i$'s are boundary operators that are not necessarily primary. It's a well-known fact that the corresponding sphere correlator is determined up to an overall constant, but I seem to be getting... | g14074 | [
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<p>If I have a spring being compressed by two bodies, A and B, with different masses, how much energy would be transferred to each one when they are released and the spring expanded?</p> | g14075 | [
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<p>In my exam today I've been given this problem, yet even with the results at hand I simply can't warp my head around it; </p>
<p>Given the picture below, a bar is placed on two conducting rails with a resistor (in the form of a single thin wire) at the left. Now at t=0 the magnetic field changes which causes the bar... | g14076 | [
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<p>Using differential forms <a href="http://em.groups.et.byu.net/pdfs/publications/formsj.pdf">and their picture interpretations</a>, I wonder if it's possible to give a nice geometric & physical motivation for the form of the Electromagnetic Lagrangian density?</p>
<p>The Lagrangian for the electromagnetic field ... | g14077 | [
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<p>How do we know for certain that space is expanding?</p>
<p>Let's say that in the year 1950, we observe that galaxy 1 is 5 billion light years away from us and galaxy 2 is 10 billion light years away from us, putting both galaxies at a distance of 5 billion light years from each other. Then in 2013, we observe that ... | g14078 | [
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<p>When I was riding a car (I was not the driver), my eardrum felt a little similar to the case when I was in a plane that was taking off, and little loss of hearing. Nothing was played inside. The feeling was gone, when I left the car. This don't happen often when I ride a car. So I wonder what might be the reason? Th... | g14079 | [
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<p>I have seen case studies of the 3D Debye model where the vibrational modes of a solid is taken to be harmonic with dispersion relation $\omega = c_sk$. It is said that for temperatures much less than the Debye temperature, the heat capacity at constant volume $$C_V\sim T^3$$.</p>
<p>Now I want to show that for boso... | g14080 | [
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<p>Schrodinger's Equation does not set a limit on the size of wave functions but to normalize a wave function a limit must be set. How is this consistent physically and mathematically with Schrodinger's Equation.</p> | g14081 | [
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<p>In AQFT one specifies the structure of the observables as a $C^*$-algebra. This seems to excludes algebras that don't have a norm, such as the Heisenberg algebra. Fortunately for this case one turns to Weyl algebra. </p>
<p>Is that trick always possible? </p>
<p><em>Additional material:</em></p>
<ul>
<li><p>Relat... | g14082 | [
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<p>I am running an animation of a satellite in an elliptic orbit (defined by a parametric equation for $x$ and $y$ as a function of $t$) and want to make sure the spacecraft is traveling at the right speeds at different points in its orbit. That is, it should go slower at is apoapsis and much faster at its periapsis. I... | g14083 | [
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<p>I have been told that the AdS/CFT correspondence proof does not rely on the validity of string theory. To be honest I don't know what to make of this. The idea of taking seriously the results of applying the techniques of this correspondence is appealing, but before I head in that direction, I need some help finding... | g14084 | [
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<p>the quadrupole formula has some counterintuitive consequences, when analysing the power output averaged over a period</p>
<p>$$ P = \langle \frac{d^3 Q_{ij}}{dt^3} \frac{d^3 Q_{ij}}{dt^3} \rangle $$</p>
<p>Specifically, if two separated sources are considered inside the radiation zone, $\rho_1$ and $\rho_2$, and a... | g14085 | [
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<p><strong>A simple explanation for photon entanglement experiments</strong></p>
<p>Example: Quantum teleportation La Palma-Teneriffa in 2012 (distance 143 km) - Photons were entangled in such a way that when measuring polarization of one of the photons (obtaining a random result) the other photon will show a perfectl... | g14086 | [
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<p>I know that <a href="http://en.wikipedia.org/wiki/Superfluidity" rel="nofollow">superfluidity</a> is caused by the fluid having zero viscosity. This only happens at very low temperature, so the fluid (e.g. Helium-4) is a Bose-Einstein condensate.</p>
<p>I also know that in a <a href="http://en.wikipedia.org/wiki/Bo... | g14087 | [
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<p>Combining the first and second law of thermodynamics we can get the following equation</p>
<p>$$TdS=dU-P_{ext}dV$$</p>
<p>First question: Is this equation applicable for irreversible processes such that that $dS≠\dfrac{dQ}{T}$?</p>
<p>Second question:If the system temperature $T_{sys}$ is smaller than the surroun... | g895 | [
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<p>In my book's thermodynamics chapter, it says that an </p>
<blockquote>
<p>"object that radiates heat faster also absorbs heat faster. This means
that an object that is a more efficient radiator comes to equilibrium
with its environment more quickly. With this in mind, is it better to
paint your house black ... | g508 | [
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<p>In quantum optics (and hence also cv quantum information), given the annihilation and creation operators of the electromagnetic fields $a$ and $a^{\dagger}$, the "position" and "momentum" operators that we can construct in analogue with the harmonic oscillator, i.e.
$$ x:=\frac{1}{\sqrt2}(a^{\dagger}+a) \quad\text{a... | g14088 | [
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<p>I'm trying to come up with a simple experiment that can demonstrate the properties of Gauss's Law for Magnetism. I am aware that it is a mathematical representation of the fact that magnetic monopoles don't exist (at least as far as we know), but are there any simple experiments that I could set up that a high scho... | g14089 | [
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<p>If, say, a particle with energy $E<V_0$, approaches a finite potential barrier with height $V_0$, and happens to tunnel through, where would the particle be during the time period when it is to the left of the potential barrier and to the right of the potential barrier? Surely there must be a finite amount of tim... | g14090 | [
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<p>What specific behaviour confirmed the existence of the W and Z bosons at the UA1 and UA2 experiments?</p>
<p>Thanks!</p> | g14091 | [
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<p>this is my first question on PhysicsSE (I'm already an user of MathSE). </p>
<p>I'm a mathematics students trying to understand Faraday's law, that is </p>
<p>$$\varepsilon= -\frac{d \Phi_B}{dt}$$</p>
<p>where $\varepsilon$ means electromotive force and </p>
<p>$$\Phi_B=\iint \mathbf{B}\cdot d\mathbf{S}$$ </p>
... | g142 | [
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<p>Two point charges, -2.5 micro coulombs and 6 micro coulombs, are separated by a distance of 1m (with the -2.5 charge on the left and 6 on the right).</p>
<p>What is the point where the electric field is zero?</p>
<p>This seems exceptionally easy, but I can't figure it out. I can calculate the answer if both charge... | g14092 | [
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<p><a href="http://en.wikipedia.org/wiki/Bessel_function" rel="nofollow">Hankel functions</a> are solutions to the scalar Helmholtz-equation $$\Delta\psi + k_e^2\psi = 0$$ in cylindrical and spherical geometry (with respect to a separated angular dependence). Thus, they are very important describing <strong>spherical</... | g14093 | [
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<p>I suspect not, because moving forward (or backwards for that matter) is an important part, but I would like to confirm.</p>
<p><strong>UPDATE</strong>: Clearly it's possible
<div style="z-index:0;">
<object style="height: 385px; width: 640px">
<param name="movie" ... | g14094 | [
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<p>The physical continuum is commonly assumed to have a mathematical continuum of points, that is, with a cardinality equinumerous with the Power Set of the set of natural numbers. However, since
[ZFC + "there exists an inaccessible cardinal"]
suffices to model analysis, and
[ZFC + "there exists an inaccessible cardi... | g14095 | [
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<p>How does one know the correct position of planets in relation to the sun when viewing the solar system from different angles makes the appearance of the planets different? I would think that it would require a satellite to orbit in a circular pattern above and below the entire solar system to get correct bearings.</... | g14096 | [
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<p>I was interested in making what I thought would be a simple simulation of an electron encountering a positron by numerically solving the Schrodinger equation over several time steps, but I've run into 1 problem: the potential used in most textbooks (to solve the hydrogen atom for example) are still of a classical p... | g14097 | [
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<p>I have a set of samples that represents a waveform. This waveform resembles a frequency modulated sinusoidal wave (only it is not).</p>
<p>I would like to invert this waveform or <strike>shift it by $2\pi$</strike> shift it by $\pi$. of course taking the cosine of samples as they are without preprocessing is wrong.... | g14098 | [
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<p>The ground state for a quantum Hall system on a torus with fractional filling factor can be classified by the Chern number, which is why the Hall conductance is quantized. Is there another method or classification one can use to distinguish states?</p> | g14099 | [
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<p>I know that sound travels faster in water compared to air and say faster in steel than in what're so
What would the density have to be to cause sound to approach the speed of light</p> | g14100 | [
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<p>It's comparatively easy (cum grano salis) to grasp the following concepts:</p>
<ul>
<li>Euclidean space-time <em>(continous space and continuous time)</em></li>
<li>classical mechanics <em>(discretely distributed matter in continous space and continuous time)</em></li>
<li>Minkowskian space <em>(continously intermi... | g14101 | [
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<p>I was reading the Wikipedia article on <a href="http://en.wikipedia.org/wiki/Lagrangian_point">Lagrangian points</a> and doing the requisite wiki walk through the various quasi-satellites of Earth when a question occurred to me:</p>
<blockquote>
<p>Could there be a stable or Lissajous orbit around the minor body ... | g14102 | [
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<p>The formula for parrallel resistors is $\frac{1}{R_T} = \frac{1}{R_1} + \frac{1}{R_2}$</p>
<p>But how can you use this formula when one of the branches is a superconductor, eg:
<img src="http://i.stack.imgur.com/ltS11.png" alt="image description"></p>
<p>Where the red resistor represents a wire with some resistanc... | g14103 | [
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<blockquote>
<p>Generate two entangled photons, send one to a message sender and the other to the intended receiver. Both the sender and the receiver recover the same piece of quantum information from the photons, then the sender scrambles the message to be sent by some reversible function determined by the quantum i... | g14104 | [
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<p>Is there any physics theory that depicts our universe as $2+1$ dimensional?</p>
<p>I heard that black holes seem to suggest that the world might be $2+1$ dimensional, so I am curious whether such theory exists?</p>
<p>Just for curiosity.</p> | g14105 | [
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<p>I have read and heard in a number of places that <em>extra dimension might be as big as $x$ mm.</em> What I'm wondering is the following:
How is length assigned to these extra dimensions? </p>
<p>I mean you can probably not get your ruler out and compare with the extent of an extra-dimension directly, can you? So i... | g706 | [
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<p>To me there seems to be quite a few different definitions of $f_{NL}$ in cosmology and I would like to know if or how they are equivalent. Let me cite at least 3 such,</p>
<ul>
<li><p>One can see the equation 6.71 on page 100 of the book "The Primordial Density Perturbation" by Liddle and Lyth. The closest one can... | g14106 | [
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<p>The fact that the bosons of the weak force have mass is something that I think technically poses many problems.</p>
<p>To avoid this and other problems with the masses of the particles devised a mechanism within the standart model $SM$ of particle physics $"smpf"$ called "the Higgs field." This field is t... | g14107 | [
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<p>I understand that for low cross-section events a very high luminosity is necessary in order to obtain enough data to produce meaningful statistics. That is why the <a href="http://en.wikipedia.org/wiki/Large_Hadron_Collider" rel="nofollow">LHC</a> was built.</p>
<p>But which are these event which we are interested ... | g14108 | [
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<p>Since outer space is not quite a vacuum, and the distribution of various heavenly bodies is locally inhomogeneous, it seems reasonable to expect that the density and variety of particles 'contaminating' the vacuum varies with time and space. Are there any maps or data sets which detail this variation?</p> | g14109 | [
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<p>We believe that time is a dimension and that $x$,$ y$, $z$ are dimensions in space. Is quantity a dimension like these? And if not, how do we have dimensionless numbers (like $e$, $\pi$ etc.)? </p> | g14110 | [
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<p>In his lectures professor Hamber said that the metric tensor is not unique, just like the 4 vector potential is not unique for a unique field in electrodynamics. Since the metric tensor is symmetric, only ten components of the metric tensor are unique. </p>
<p>However, as the covariant divergence of the Einstein's ... | g14111 | [
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<p>"A bar magnet is moved towards a freely hanging coil. Determine if the coil stays stationary or not. If it moves, determine if it moves away or towards the magnet."</p>
<p>My hypothesis: From Lenz's law an e.m.f will be induced in the coil to oppose the change in magnetic flux due to the relative approach of the b... | g14112 | [
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<p>Our universe has a finite size. It is often called the "radius of the universe", or "distance of the cosmic horizon".</p>
<p>If we would fly with relativistic speed at the position of our Earth, would this finite size Lorentz-contract? Or would it stay the same?</p>
<p>In simple words: Does the universe Lorentz-co... | g14113 | [
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<p>I have this childrens rubber ball which glows in the dark after it's exposed to light. I "charge" it with a flash light then play with my dogs at night. I thought to try a very intense green laser, and see how the ball reacted.</p>
<p>The laser light had no effect on the balls ability to glow. So I'm left wondering... | g14114 | [
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<p>So, how do we know $J_{+}|j,(m=j)\rangle =|0\rangle$?</p>
<p>I.e. that m is bounded by j.</p>
<p>We know that $J_{+}|j,(m=j)\rangle =C|j, j+1\rangle$, but how do I know that gives zero? Is it by looking at its norm-square?</p> | g14115 | [
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<p>This is a problem in a college physics textbook, and its bugging me that I can't get it. </p>
<p>The figure shows a circuit model for the transmission of an electrical signal, such as cable TV, to a large number of subscribers. Each subscriber connects a load resistance RL between the transmission line and the grou... | g14116 | [
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<p>The situation I am looking at is a magneto-static problem of a finite magnetic film with magnetization $\bf{M}$. I would like to find the the magnetic field far above the plate. My expectation is that far above the plate, the field should approach the dipolar field which scales as $1/r^3$. However my numerical calcu... | g14117 | [
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<p>I have encountered the minimal coupling between a field and charges before $$H = \frac{1}{2m}(p-qA)^2,$$</p>
<p>whereby I am considering the classical case. </p>
<p>The description minimal leads me to ask if there exist <a href="http://www.google.com/#q=exotic+couplings" rel="nofollow">exotic couplings</a> (non-mi... | g14118 | [
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<p>How did gunsmiths create revolver cylinders holes in 1850's without the use of electrical drill?</p>
<p>Which referces/ books specialize providing knowledge in similar molding method?</p> | g14119 | [
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<p>I have a question which asks me to determine what x is for the following nuclear transition</p>
<p>$$^{29}Si(\alpha, n)X$$</p>
<p>But I don't have any idea what this notation implies.</p>
<p>Another example:</p>
<p>$$^{111}Cd(n,x)^{112}Cd$$</p> | g14120 | [
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<p>(I don't have a direct reference so this is a little fishy and I'll delete it if nobody recognises what I'm talking about, but I though for starters I'll ask anyway)</p>
<p>I've heard at university that if you have a operator (linear Hilbert space operator?) which is bounded on a restricted (compact?) domain, then ... | g14121 | [
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<p>On Earth, UVB (280nm - 315nm or 320nm depending on the source) undergoes extensive attenuation through the atmosphere, when observed at the planet's surface, as illustrated below:</p>
<p><img src="http://i.stack.imgur.com/utbcZ.png" alt="enter image description here"></p>
<p><a href="http://en.wikipedia.org/wiki/U... | g14122 | [
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<p>Quantum levitation, flux pinning -- basically, when a superconductor floats above a permanent magnet, is really fascinating. But does the strength of the magnetic field influence the superconductor's height? And what relationship/formula suggests this?</p>
<p>For example, if I had a coil wrapped around a metal obje... | g14123 | [
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<p>As a picture is worth a thousand words, here is my problem:</p>
<p><img src="http://s21.postimage.org/rv7a0t8br/problem_pressure.png" alt="Picture here"></p>
<p>It is a closed water column with a bit of air in the top section.
If I run the pump and make the water flow from IN to OUT,</p>
<ol>
<li>Will the level s... | g14124 | [
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<p>I am getting into friction on an atomic scale. For instance, take two rigid layers of atoms of the kind A that are placed on top of each other, just like putting two boards of wood on top of each other. Then place some atoms or molecules of the kind B between those two rigid layers, i.e. put some pebbles between the... | g14125 | [
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<p>I got to read Feynman vol I and there was written that at absolute zero, molecular motion doesn't cease at all, because if so happens, we will be able to make precise determination of position and momentum of the atom. But we do know that Heisenberg uncertainty principle holds for microscopic particle IN MOTION....... | g14126 | [
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<p>Lets say i have density Matrix on the usual base</p>
<p>$$ \rho = \left(
\begin{array}{cccc}
\frac{3}{14} & \frac{3}{14} & 0 & 0 \\
\frac{3}{14} & \frac{3}{14} & 0 & 0 \\
0 & 0 & 0 & 0 \\
0 & 0 & 0 & \frac{4}{7} \\
\end{array}
\right) $$</p>
<p>from this two stat... | g14127 | [
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<p>This is a simple question. Does the Energy create both Fermion and Boson particles ? or just only the Fermion particles?</p> | g14128 | [
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<p>I have what may be a dummy question. In NMR or in the study of liquid crystals for example, an order parameter $S$ is often used:
$$
S=\left\langle\frac{1}{2}\left(3\cos^2\theta−1\right)\right\rangle
$$
with $\theta$ the angle of the molecule with a "director" (the magnetic field in NMR, the normal to a membrane for... | g14129 | [
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<p>I am trying to understand pure and mixed states better. If I have N quantum particles in an isolated system. The many-particle state is a superposition of the product of single-particle states by the appropriate statistics (bosons, fermions, or distinguishable). Would this state be still considered pure since there... | g14130 | [
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0.011341562494635582,
-0.017149852588772774,
-0.028498049825429916,
-0.013602000661194324,
0.03615584596991539,
0.056425802409648895,
0.06680183112621307,
-0.0538487546145916,
-0.0707504078745842,
-0.0015103694749996066,
0.025306088849902153,
0.0... |
<p>I have an aluminium baking plate that I did put in a very hot oven and now it is soft, so I can bend it or almost roll it up. Why? </p> | g14131 | [
0.03735506907105446,
0.04982433095574379,
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0.037313349545001984,
0.016083355993032455,
0.012665251269936562,
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0.086790531873703,
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0.0016064484370872378,
0.060019999742507935,
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0.0... |
<p>I am having an hard time trying to understand why the radiated power per unit area $P$ of a black body is given by
$$P=\frac{c}{4} u$$
in terms of the energy density $u$ and the velocity of light.</p>
<p>I know there is a derivation in <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/radpow.html" rel="n... | g14132 | [
0.05139514431357384,
0.07192840427160263,
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0.05993044376373291,
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0.040946006774902344,
0.042602650821208954,
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0.015234467573463917,
0.01830214075744152,
0.002446805825456977,
0.017... |
<p>Quantum mechanics is non-local in that long distance correlations are present, though there is no signalling possible. But QFT is Lorentz invariant and contains quantum mechanics as a special case. I assume this is not a paradox as paradoxes do not exist but I do not understand the details. Can anyone supply a refer... | g14133 | [
0.04129553958773613,
0.023982133716344833,
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0.04151461273431778,
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0.01772642694413662,
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0.02945587784051895,
0.012270772829651833,
-0.0... |
<p>Almost every book and article I can think of represents states of QFT using the Heisenberg picture of Hilbert space vectors, but Visser in "Lorentzian wormholes" does mention that you can also represent them as a functional.</p>
<p>It is very briefly mentionned, and he does not mention any sources for it, just the ... | g14134 | [
-0.0075330669060349464,
0.062392089515924454,
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0.03857526555657387,
0.0019293419318273664,
0.02161235734820366,
0.017788918688893318,
-0.03669709339737892,
0.005907665006816387,
0.0348551981151104,
0.05... |
<p>Why is it that the bound charge is $Q_b = - \oint_S{\mathbf{P} \cdot d\mathbf{S}}$? In particular, why is there a negative sign? Hayt's book on electromagnetism describes this as the "net increase in bound charge within the closed surface". Compared to Gauss' law $Q_{f} = \oint_S{\mathbf{D} \cdot d\mathbf{S}}$, th... | g14135 | [
0.04168824106454849,
0.009791376069188118,
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0.050482675433158875,
0.02852640300989151,
0.04191518574953079,
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0.05632123723626137,
0.05691416189074516,
-0... |
<p>What aspects of "conventional" quantum field theory (i.e. what's used by most practicing physicists) are considered to be lacking mathematical rigor? </p> | g14136 | [
-0.03125028312206268,
0.033979322761297226,
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0.002079879632219672,
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0.032969940453767776,
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0.017615992575883865,
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0.021612612530589104,
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... |
<p>There's a question I've come across that I've got some confusion on. </p>
<blockquote>
<p>A drum of mass $M_A$ and radius $a$ rotates freely with initial angular speed $\omega _0$. A second drum of radius $b>a$ and mass $M_B$ is mounted on the same axis, although it is free to rotate. A thin layer of sand $M_s... | g14137 | [
0.11383721232414246,
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0.018623111769557,
0.002385925967246294,
0.04063199833035469,
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0.10875997692346573,
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0.032317645847797394,
-0.008930725045502186,
0.0144179... |
<p>I have to Taylor expand an effective potential $U_{eff}$, which is given by:</p>
<p>$$U_{eff}(r)=-\frac{Gm_{1}m_{2}}{r}+\frac{l^{2}}{2\mu r^{2}}$$</p>
<p>I then expand it and get:</p>
<p>$$U_{eff}(r)=U_{eff}(r_{min})+\frac{dU_{eff}}{dr}\bigg|_{r=r_{min}}(r-r_{min}) +\frac{1}{2}\frac{d^{2}U_{eff}}{dr^{2}}\bigg|_{r... | g14138 | [
0.016705958172678947,
0.004654869902879,
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0.019848693162202835,
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0.019306911155581474,
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-0.0014747491804882884,
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0.08016598969697952,
0.048093393445014954,
-... |
<p>I want to show:$$ Tr\left (F\tilde{F} \right )=\partial_{\mu}K^{\mu }=\partial_{\mu}\left (\varepsilon _{\mu \nu \rho \sigma }Tr\left ( F_{\nu \varrho }A_{\sigma }-\frac{2}{3}A_{\nu }A_{\rho }A_{\sigma} \right )\right ).$$</p> | g14139 | [
0.021908055990934372,
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0.033875472843647,
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<p>I am reading Jackson, Classical Electrodynamics, and I have a question regarding the electrodynamic <a href="http://en.wikipedia.org/wiki/Multipole_expansion" rel="nofollow">multipole expansion</a> (with page numbers I refer to the 3rd edition). So on page 409, he gives in equation 9.9 the general formula for the ex... | g14140 | [
0.026389071717858315,
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0.02115613967180252,
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0.03175296634435654,
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0.03287486732006073,
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<p>A spherical capacitor with inner radius $r_1$ and outer radius $r_2$ is filled with dielectric material with permittivity $\epsilon=\epsilon_0+\epsilon_1\cos^2\theta $.<br>
$\theta$ is the polar angle. Furthermore there is a charge $Q$ on the inner surface at $r_1$ and a charge $-Q$ on the surface at $r_2$. </p>
<... | g14141 | [
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0.0664958730340004,
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0.061715275049209595,
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<p>We measure distances in universe by the units of light year/s or parsec. Which means distance traveled by light in one year equals one light year. Thus the lights we receive from the distant stars or galaxies are coming from many light years away.</p>
<p>So how do we know the age of the light so that we determine t... | g14142 | [
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0.020398076623678207,
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0.0962827056646347,
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<p>I recently read an article on dark matter and I could understand this things given as follows
All the ordinary matter we can find accounts for only about 4 percent of the universe. We know this by calculating how much mass would be needed to hold galaxies together and cause them to move about the way they do when t... | g438 | [
0.04521794244647026,
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0.029138052836060524,
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0.038144927471876144,
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<p>I've been learning about pressure and fluid dynamics, and I've stumbled onto a problem. Say you have a straw in a cup. The surface area of the water in the cup is much greater than that of the straw. </p>
<p>So, I would expect Atm. Pressure × Large Area (of the cup) gives a <em>much</em> greater force than Atm. Pre... | g14143 | [
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0.04810831695795059,
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0.05208073556423187,
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<p>In some specifications for telescopes, I saw a value marked as f/4.6. What does it mean exactly, and how important is when it comes to choosing a telescope?</p> | g14144 | [
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0.11240722984075546,
... |
<p>The $E$ string of a violin has a linear density of $0.5 g / m$ and is subjected to a
$80\text{N}$ of tension, tuned for a frequency $u = 660 \text{Hz}$:</p>
<ol>
<li>What is the length of the rope?</li>
</ol>
<p>I know that in order to answer the question I have manipulate the equation:</p>
<p>$$
\nu = \sqrt\fra... | g14145 | [
0.044752202928066254,
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0.029103726148605347,
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<p>Assuming two stars are 1 light year apart and a traveler is travelling at 0.75 of $c$, from the point of view of the traveler what would be the observed time en route? Also, if a vehicle is constantly accelerating, will it reach 0.75 of $c$ within a reasonable amount of time? What would the Lorenz transforms look li... | g14146 | [
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... |
<p>I wanted to know how a radio frequency accelerating cavity actually works. I know that an electric field is used to accelerate the charged particles. However, is this done by using metal plates with opposite polarities or are there tubes (like in the linac) within the accelerating cavity which have fields in between... | g439 | [
0.04862663149833679,
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0.03526337817311287,
0.04330039396882057,
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<p>I know that when photons pass through matter, the law that describes the intensity in function of the thickness is:</p>
<p>$$I(x)=I_0 e^{-\mu x}$$ </p>
<p>where $\mu = \rho \frac{N_a}{A} \sigma$ and $\rho$=density of the matter, $N_a$= Avogadro constant, A= mass number of the matter and $\sigma$=cross section.</p>... | g14147 | [
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0.036217521876096725,
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<p>Usually one finds this expression for the low energy action</p>
<p>$$S = \frac{1}{2\kappa_0^2}\int d^D X\; \sqrt{-G}\; \mathrm{e}^{-2\Phi}\,(R-\frac{1}{12}H_{\mu\nu\lambda}H^{\mu\nu\lambda}+4 \partial_{\mu}\Phi\partial^{\mu}\Phi).$$</p>
<p>On dimensional grounds one can deduce $\kappa_0^2$ near $\ell_s^{24}$ (for ... | g14148 | [
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<p>Questions first, then my rough estimations:</p>
<p>1) Is it possible to perform moon laser ranging with amateur motorized 114mm telescope? My calculations suggest that for 1mJ laser it should receive ~2 photons per source 1mJ laser pulse. </p>
<p>2) Given that we already talking about individual photons, how it wa... | g14149 | [
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<p><img src="http://i.stack.imgur.com/nXoEe.jpg" alt="enter image description here"></p>
<p>I cannot understand how and why those two expressions are coming (the ones I have highlighted). Please explain.</p> | g14150 | [
0.01196750532835722,
0.005113745573908091,
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0.000943138322327286,
0.0644972026348114,
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0.029299437999725342,
0.06097925826907158,
0.044... |
<p>$\int\frac{GMm}{x^2}dx$ where $x$ varies from $\infty$ to $r$.</p>
<p>Situation we are bringing a very small mass from infinity to a distance r in the gravitational field of Earth with constant velocity(distances are measured between earth and small mass).
now work done by gravity is $\int\frac{GMm}{x^2}dx$ (where ... | g14151 | [
0.02712845243513584,
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<p>In another StackExchange Physics question, @Rego had found the following equation to calculate the lift force generated by <strong>a simple rectangular blade</strong>.</p>
<blockquote>
<p>$$F = \omega^2 L^2 l\rho\sin^2\phi$$
in which $\omega$ is the angular velocity, $L$ is the lenght of the helix, $l$ is the ... | g14152 | [
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<p>I am having trouble understanding how the following statement (taken from some old notes) is true:</p>
<blockquote>
<p>For a 2 dimensional space such that $$ds^2=\frac{1}{u^2}(-du^2+dv^2)$$
the timelike geodesics are given by $$u^2=v^2+av+b$$ where $a,b$ are constants.</p>
</blockquote>
<p>When I see "geodesic... | g14153 | [
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<p>I understand einstein's train paradox. Where one man on a platform is passed by a man in a traincar, at the moment they meet a flash of light is given off in the middle of the train car. To the man on the platform the light hits the ends of the car at opposite moments in time. To the man in the train car they hit at... | g14154 | [
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-0.... |
<p>I understand that the massless fields of the Type I string theory are the described by:
[\begin{array}{*{20}{c}}
{{\rm{Sector}}}&{{\rm{Massless fields}}}\\
{{\rm{R - R}}}&{{C_0}}\\
{{\rm{NS - NS}}}&{{g_{\mu \nu }},\Phi }\\
{{\rm{R - NS}}}&{{\Psi _\mu }}\\
{{\rm{NS - R}}}&{\lambda'}\\
{\rm{R}}&... | g14155 | [
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0.008154467679560184,
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... |
<p>How does the path of light become visible due to scaterring of light? According to me it will only tell the presence of colloidal particle but the book give the example of cinema hall projector and says that you could tell path of light due to scattering of light. Nevertheless, without scaterring of light also we ca... | g14156 | [
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0.08480313420295715,
0.03432744... |
<p>Suppose I wrap wire around a bar magnet, creating a solenoid such that the poles of a bar magnet and the poles of solenoid are opposite to each other. If I were to hold a compass near one side, which pole would the compass detect? That of the bar magnet or of the solenoid?</p> | g14157 | [
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0.0... |
<p>Take an shell or bubble.
The bubble is strong enough to maintain it's static sphere shape, except when a photon bounces off the inner surface.</p>
<p>A photon fires from inside the bubble.</p>
<p>The inner surface gets pelted by this photon, and the inner surface bounces it back similar to a trampoline bounce. The... | g14158 | [
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<p>Please forgive: I am a layman when it comes to physics and cosmology, and have tried finding an answer to this that I can understand, with no luck.</p>
<p>As I understand it, the solar system evolved from a massive molecular cloud. To me, this seems to break the second law of thermodynamics, as I think it suggests ... | g779 | [
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<p>I have to use the Green's function for the 2D Helmholz equation
$$(-\nabla^2 - E) \psi(x, y) = 0$$ on the rectangular domain $[0, L_x] \times [0, L_y]$ with Dirichlet boundary conditions:
$$\psi(0, y) = \psi(L_x, y) = \psi(x, 0) = \psi(x, L_y) = 0$$ in my calculations. </p>
<p>To get the Green's function I used eig... | g14159 | [
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<p>I read photons do not age because they move at the speed of light. So when a photon interacts with my eyes, aren't they apart in space-time by the difference of the time in the frame of reference of the eye and the time when the photon started traveling?</p>
<p>I guess I am imagining a 4D-space here. What is my err... | g14160 | [
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<p>I recently followed courses on QFT and the subject of renormalization was discussed in some detail, largely following Peskin and Schroeder's book. However, the chapter on the renomalization group is giving me headaches and I think there are many conceptual issues which are explained in a way that is too abstract for... | g14161 | [
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<p>Is it possible for a massless particle to undergo zitterbewegung? In massive Dirac theory the Zitterbewegung frequency comes out to be $2mc^2/\hbar$. It looks like the effect will vanish for a massless particle. But the effect is due to the interference between particle and antiparticle state which is also there for... | g14162 | [
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<blockquote>
<p><strong>Premises And the Conclusion of the Paradox</strong>: (1) When the arrow is in a place just its own size, it’s at rest. (2) At every moment of its flight, the arrow is in a place just its own size. (3) Therefore, at every moment of its flight, the arrow is at rest.</p>
</blockquote>
<p>If some... | g14163 | [
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... |
<p>I'm doing magnification and lens in class currently, and I really don't get why virtual and real images are called what they are.</p>
<p>A virtual image occurs the object is less than the focal length of the lens from the lens, and a real image occurs when an object is further than focal length.</p>
<p>By why virt... | g209 | [
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