dialog listlengths 4 30 | title stringlengths 15 150 | category stringclasses 14 values | dialog_time stringdate 2016-01-21 01:59:30 2018-07-01 01:34:46 |
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[
{
"message": "i have 3 markers and when i hover on the marker, i want the marker to get enlarged. can anyone help me to solve this. I had tried to change the pointer on mouseover but not getting how to enlarge marker on hover.TS:<pre><code> mapboxgl.accessToken = 'pk.eyJ1IjoicmFrc2hpdGhhMTkiLCJhIjoiY2pjcHl... | How to enlarge the marker on mouseover in mapbox gl js | gis | 2018-01-24T07:56:18.963 |
[
{
"message": "I try to calculate raster distance to restaurants using proximity in QGIS. I have the following data:Binary Int Raster with restaurant location Perimeter Shapefile Using QGIS GDAL Proximity, I got this error message, which I don't understand:<a href=\"https://i.stack.imgur.com/j9uSb.png\" rel=\"no... | Defining extent of SAGA proximity algorithm output | gis | 2018-01-24T12:28:17.110 |
[
{
"message": "I write a request that allows to snap a point to another.Here is the request:<pre><code> SELECT f.gid as gid, ST_Snap (f.Geom, g.Geom, min, 5) as geom FROM boiten as f, (SELECT ST_Collect (Geom) as Geom FROM ft_chambre) as g</code></pre>It works but the snapped p... | Snap point to point with St_Snap Postgis | gis | 2018-01-24T15:11:00.357 |
[
{
"message": "I've installed QGIS 2.99 to test its new features, particularly the 3D viewer, when I try the following I only see a square, not a 3D cube.In PostGIS I make a square and extrude it<pre><code>-- make a squareCREATE TABLE public.square1( id serial, geom geometry, CONSTRAINT square1_pkey PRI... | Viewing polyhedrals through the new 3D viewer QGIS 2.99 (3.0) | gis | 2018-01-24T16:41:56.550 |
[
{
"message": "I previously had 10.5 and opened up an ArcGIS 10.2 versions MXD. This week, I upgraded to 10.6 and tried to open the MXD from that same 10.2. That MXD would not open. All it would do is \"not responding\". I copied, renamed it and even re-downloaded it from the email it was sent from. Nothing.... | ArcGIS 10.6 opening mxd from 10.2 | gis | 2018-01-24T22:10:09.160 |
[
{
"message": "I am looking for an mobile multi-platform (or at least Android) application which will allow me to share my spatial data.On day to day bases I am working with QGIS in archaeology and with Losuc GIS in the field. I have developed some interpretaions (remote sensing based) which I would like to shar... | Mobile "GIS"/geolocalization application for popularisation of science? | gis | 2018-01-25T10:32:16.217 |
[
{
"message": "I'm trying to plot some cities stored in my rda file <code>naobrazokSR.rda</code> on a map from <code>GADM</code> while having a background of the map in color <code>#2C3E4F</code>. Without using the <code>coord_map()</code> this works as intended but looks deformed. After using the <code>coord_ma... | Ggplot2 map with colored background and coord_map() | gis | 2018-01-25T12:57:12.880 |
[
{
"message": "I want to create a center line for a river (polygon). I thought about simply creating a new line manually, but it would be a long and imperfect process. If there is a way to automate this process, that would be much better. Can anyone help?",
"role": "user"
},
{
"message": "I would try... | Create a center line between 2 polyline - QGIS | gis | 2018-01-25T14:48:33.747 |
[
{
"message": "I am creating a model that finds all the tracks(points) a wolf pack leaves who cross into a park using select by location, easy. I than want to find all the tracks(points) those same wolfs made on those same trips before and after leaving the park. The problem I am having is after the first featur... | modelbuilder stuck values during iterating | gis | 2018-01-25T21:06:44.890 |
[
{
"message": "I have QGIS 2.18.3 installed. I'm trying to change angle units from degrees to Gon/gradians (90 degrees = 100 Gon).I navigated to Settings--> Options --> Map Tools --> Preferred angle units, and changed it from \"degrees\" to \"Gon/gradians\".It seems that Gons/Gradians are applied to measurement ... | Advanced Digitizing Panel angle units | gis | 2018-01-26T11:20:44.263 |
[
{
"message": "Apparently, the new released SNAP 6.0 allows the sen2cor plugin to be installed and run directly within the SNAP. Indeed, SNAP installs the bundle when try to run it.However, it doesn't work for me. Although a new folder is generated (S2A_MSIL1A...from the S2A_MSIL1C), the folder does not contain ... | sen2cor 2.4.0 on SNAP 6.0 | gis | 2018-01-26T11:30:46.230 |
[
{
"message": "I have QGIS 2.18.3 installed. I'm trying to create a printable .pdf map with QGIS Print Composer. It needs to have X & Y coordinates listed in an attribute table, with 3 decimals accuracy.Print Composer has a separate button for \"Add attribute table\". I added the table using this feature, bu... | Attribute table trailing zeroes missing in Print Composer | gis | 2018-01-26T11:48:00.697 |
[
{
"message": "I have difficulties generating 3D contour lines from a raster file in QGIS. It's a tif raster of an elevation model that I exported from a professor's ArcGIS project. I want to create contour lines in order to import them into SketchUP to design some engineering biological measures. Every time I u... | Generating 3D contours instead of 2D lines from a raster | gis | 2018-01-27T19:17:57.263 |
[
{
"message": "Trying to use Numerical Digitize 0.3.0 in QGIS 2.18.15. I have both that plugin and Numerical Vertex Edit installed, and I can see both icons (greyed) on the Digitize toolbar.I create a new point layer, enable editing, and click the Add Feature button. Both of these buttons remain grey and unclick... | QGIS Numerical Digitize button always greyed out? | gis | 2018-01-29T12:33:54.377 |
[
{
"message": "I was wondering if anyone knew where I could find some documentation on proper syntax for use of wildcards in arcpy, such as with the ListFeatureClasses function?I have been unable to locate any thus far.",
"role": "user"
},
{
"message": "There is an ArcPy Café blog posting on this sub... | Documentation on wildcard syntax, such as for use in arcpy.ListFeatureClasses()? | gis | 2018-01-29T16:08:54.160 |
[
{
"message": "Problem<blockquote> For simplicity, let's consider a two dimensional problem. A plane wave is incident from $x$ axis: $$ \\psi_{inc}=e^{ikx} $$ The 2D Hamiltonian reads: $$ H=\\hat{p}_x^2+\\alpha \\hat{p}_y^2 +V(r) $$ where $\\alpha>0$ but $\\alpha\\neq1$. $V(r)=+\\infty$ when $x^2+y^2<... | Quantum scattering problem in anisotropic medium | physics | 2017-04-14T11:47:03.890 |
[
{
"message": "<a href=\"https://www.youtube.com/watch?v=dihQuwrf9yQ\" rel=\"noreferrer\">This video has a nice description of resonance inside a <a href=\"https://en.wikipedia.org/wiki/Rubens%27_tube\" rel=\"noreferrer\">Rubens' tube, and it has some pretty nice visuals of the tube being driven at the precise r... | What is the waveform for a Rubens' tube driven slightly off-resonance? | physics | 2017-04-14T15:15:57.120 |
[
{
"message": "Lets say we shoot a rocket from Earth and assume it starts with a base velocity. For something close to Earth one would use this to calculate its height depending on time etc.$$\\frac{1}{2}at^2 + v_0t + h_0 = h(t)$$If we try to calculate its height, we have to consider that the acceleration drops ... | Calculate rocket trajectory | physics | 2017-04-14T18:01:07.583 |
[
{
"message": "A Moebius strip is a simple example of a non orientable surface. Suppose a very thin metal model of one, say of length $2\\pi L$ (midline), width a, thickness negligible is perturbed (\"kicked\"), and then left to freely vibrate transversely. How do its vibrations differ compared to those of a ... | What are the eigenfunctions and eigenvalues of a moebius strip? | physics | 2017-04-15T01:08:11.137 |
[
{
"message": "We have studied that electron's position around the nucleus is given by probability distribution function, which determines the shape of atomic orbitals. Does the shapes of orbitals change with factors such as electric fields, magnetic fields, high temperatures, intense gravitational fields even w... | Change in shape of Atomic Orbitals | physics | 2017-04-15T08:16:30.087 |
[
{
"message": "Consider for example the next changess:<a href=\"https://i.stack.imgur.com/97wSA.jpg\" rel=\"nofollow noreferrer\"><a href=\"https://i.stack.imgur.com/mG7qI.png\" rel=\"nofollow noreferrer\">The change of a Higgs and the change of a muon [in the diagram of which we also see the decay of (virtual) ... | How can a truly elementary particle change into other particles? | physics | 2017-04-15T11:38:48.737 |
[
{
"message": "For counting, we use thousand, million, billion, trillion etc. For physical quantities, thousand becomes Kilo, million is Mega and (<a href=\"https://en.wikipedia.org/wiki/Long_and_short_scales\" rel=\"nofollow noreferrer\">short scale) billion is Giga. In both these systems, the consecutive prefi... | Why do physical units have different prefixes than the ones used for counting? | physics | 2017-04-15T15:05:53.933 |
[
{
"message": "Action of a particle is written as $$S[q]=\\int dt\\hspace{0.2cm} L(q(t),\\dot{q}(t),t).$$ How can I understand why $S$ is a functional of $q$, and not that of $\\dot{q}$? Assuming $L=\\frac{1}{2}m\\dot{q}^2-V(q)$ and $V(q)=\\alpha q^2$ (as an example), how can I understand that $S=S[q]$ and $S\\n... | Why is action a functional of $q$ only? | physics | 2017-04-15T18:07:24.073 |
[
{
"message": "[Editorial note: I'm going to revise this question according to the suggestions made in comments and answers during the next few days. Thank you all for your valuable hints.]There's the \"ant on a ballon's surface\" story that's often told if it comes to trying to unravel the knot in people's brai... | Is this a reasonable explanation for "the universe is finite but unbounded" which seems to be contradictory at first sight? | physics | 2017-04-16T03:31:31.313 |
[
{
"message": "The probability distribution for an observable with a discrete spectrum is defined by an inner product operation (and implemented as a dot product) on its wave function. $$\\langle \\psi|\\psi\\rangle$$ If $\\psi$ is expressed as a superposition of eigenvectors $\\left\\{|\\psi_1\\rangle,|\\psi_2\... | Is quantum interference only observed for observables that have a continuous spectrum? | physics | 2017-04-16T15:44:21.867 |
[
{
"message": "If a plane mirror is rotated by an angle $\\theta$ ( keeping the incident ray fixed) then the reflected ray gets rotated by angle $2\\theta$.Does this happen with a Spherical mirror too i.e for paraxial rays?According to me, it will be true for paraxial rays since spherical mirrors are assumed to ... | Rotating a Spherical Mirror | physics | 2017-04-16T17:22:49.030 |
[
{
"message": "As I understood my Feynman diagrams are nothing more like pictures for the transition amplitueds (up to some orders). For this we introduce a interaction vacuum state $|\\Omega\\rangle$then we are able to calculate:$$\\langle\\Omega|T\\{\\phi(x_1)...\\phi(x_n)\\}|\\Omega\\rangle.$$I thougth this m... | Transition amplitude for QED+QFD+QCD interactions | physics | 2017-04-17T09:57:02.007 |
[
{
"message": "Two Questions: Field lines are always drawn perpendicular to the surfaces at the point of contact, what does that say about the physical electric field ( or why are they drawn as so not with an angle or parallel or otherwise. ) If ( according to my understanding ) field lines are lines of forces t... | How electric field lines are drawn | physics | 2017-04-17T11:44:30.163 |
[
{
"message": "Dipolar charge distributions are essentially all the same: regardless of how one adds up a combination of the form$$\\sigma(\\theta,\\varphi) = \\operatorname{Re}\\left[\\sum_{m=-1}^1 a_m Y_{1m}(\\theta,\\varphi)\\right],$$you only ever get a rotated version of the canonical $Y_{10}(\\theta,\\varp... | How many truly different multipolar charge distributions are there? | physics | 2017-04-17T12:36:19.517 |
[
{
"message": "Dipolar charge distributions are essentially all the same: regardless of how one adds up a combination of the form$$\\sigma(\\theta,\\varphi) = \\operatorname{Re}\\left[\\sum_{m=-1}^1 a_m Y_{1m}(\\theta,\\varphi)\\right],$$you only ever get a rotated version of the canonical $Y_{10}(\\theta,\\varp... | How many truly different multipolar charge distributions are there? | physics | 2017-04-17T12:36:19.517 |
[
{
"message": "In QM the norm of the wave function $\\psi(\\vec{x})$ is said to be the probability density that the particle is at $\\psi(\\vec{x})$ if one would observe its position. Generally, nothing more is explained what this exactly means, yet I'm confused by it. Hence my question: Does it mean that any gi... | What precisely is the wave function a probability density of? | physics | 2017-04-18T01:55:44.353 |
[
{
"message": "In QM the norm of the wave function $\\psi(\\vec{x})$ is said to be the probability density that the particle is at $\\psi(\\vec{x})$ if one would observe its position. Generally, nothing more is explained what this exactly means, yet I'm confused by it. Hence my question: Does it mean that any gi... | What precisely is the wave function a probability density of? | physics | 2017-04-18T01:55:44.353 |
[
{
"message": "Could anyone explain the differences between the photoelectric effect and the Compton effect in a complete but perceptible form?",
"role": "user"
},
{
"message": "You might want to check out this answer <a href=\"https://physics.stackexchange.com/questions/31581/compton-scattering-vs-p... | Diferences between photoelectric effect and the Compton effect | physics | 2017-04-18T20:02:25.693 |
[
{
"message": "I've been struggling with understanding basic spacetime diagrams in the first chapter of Schutz's book on General Relativity. I don't get why the slope of the t prime axis of a moving observer is 1/beta. I can understand how using the Lorenz derivations will give you such a result but Schutz prese... | Schutz and spacetime diagrams | physics | 2017-04-18T23:09:59.617 |
[
{
"message": "In standard quantum mechanics textbooks, the concept of operators is often introduced as linear maps that map a Hilbert space $H$ onto itself:$$\\hat{O}: H \\rightarrow H \\, .$$However, directly after, we use the position operator $\\hat{\\vec{x}}$, which isn't of the said shape, but instead is l... | Rigorous mathematical definition of vector operator? | physics | 2017-04-19T00:16:18.733 |
[
{
"message": "For Noether theorem with only internal symmetry, I've found <a href=\"https://physics.stackexchange.com/q/56905\">there has been a very clear proof. But I still struggle with the proof of coordinate transformation. Because there are so many different proofs which are not consistent with each oth... | Big puzzle about Noether's theorem of coordinate transformation (spacetime symmetry) | physics | 2017-04-19T01:26:02.680 |
[
{
"message": "My instructor put in the notes a picture of a loop without an inductor -just a battery with voltage $\\epsilon$, a switch, and resistor with resistance $R$. He explains that as soon as the switch is flipped, an emf is created that will oppose the change in flux. With an inductor, I can see how thi... | No inductor - any induced EMF when switch flipped on? | physics | 2017-04-19T04:00:58.323 |
[
{
"message": "I am looking for an understanding which shows that conservation of momentum is not violated while observing Casimir effect? The link for Casimir effect is <a href=\"https://en.wikipedia.org/wiki/Casimir_effect\" rel=\"nofollow noreferrer\">https://en.wikipedia.org/wiki/Casimir_effectIt appears we ... | Conservation of momentum/energy and Casimir effect? | physics | 2017-04-19T04:15:50.287 |
[
{
"message": "When dealing with circular polarizations, spherical harmonics, and generally with any vector-valued rotationally-invariant quantity, it is often a requirement to define complex-valued unit vectors of the form $(1,i,0)$ and $(1,-i,0)$, which have the nice property that under a rotation they go to t... | Why are circular unit vectors often defined as $\hat{\mathbf e}_\pm = \mp (\hat{\mathbf e}_x \pm i \hat{\mathbf e}_y)/\sqrt{2}$ | physics | 2017-04-19T10:35:55.700 |
[
{
"message": "I have two questions that i didn't find in books.When calculate time rates of change of the expectation values of $\\langle x \\rangle$ or $\\langle p_x \\rangle$, why is x or $p_x$ not derived from time?Now i want to show this, if $\\Psi(r, t) $ is a square integrable wave function normalised to ... | Find operator of $[x², px]$ to calculate a expectation value of $d \langle x² \rangle/dt$ | physics | 2017-04-19T11:04:46.137 |
[
{
"message": "In order to explain the colour of an atom or molecule⁺, one considers the orbitals of the electrons surrounding it and the respective energy level differences. A single free electron does however not possess any \"self-orbital\", and thus no colour in this sense. But let's consider higher incoming... | What colour is an electron? | physics | 2017-04-19T11:45:02.457 |
[
{
"message": "The value of the free convective heat transfer for water vary between: $50$ to $3000 (W/(m^2K))$. What is it that makes it vary?",
"role": "user"
},
{
"message": "Free (often called natural) convection is fairly complex and relies on a large number of factors.You can see on <a href=\... | Free convective heat transfer for water | physics | 2017-04-19T19:49:39.733 |
[
{
"message": "I learned from <a href=\"https://www.math.ubc.ca/~feldman/apps/vlPendulum.pdf\" rel=\"nofollow noreferrer\">https://www.math.ubc.ca/~feldman/apps/vlPendulum.pdf that the equation of motion for a pendulum of variable length is$$l\\ddot{\\theta} + 2 \\dot{l}\\dot{\\theta} + g \\sin \\theta = 0$$But ... | Equation of motion for pendulum with variable length | physics | 2017-04-19T20:58:41.927 |
[
{
"message": "Disclaimer: I have this doubt due to lack of knowledge, please clear my doubt without closing it or keeping it on hold. my doubt could be silly but please clarify the doubt.So my knowledge of gravitational waves is just ripples in the space time fabric and that is what most people believe. But can... | Gravitational Waves could be just vibrations in space and not spacetime fabric | physics | 2017-04-20T05:22:55.293 |
[
{
"message": "Electroweak theory argues that the symmetry that accompanies them is obvious only to the high energies, while it is hidden with inferior energies. Scientist use top analogy to explain this concept but for me this image is improper, it does not explain well why at low energies the symmetry breaks d... | Why in the electroweak theory is symmetry 'hidden' at low energies? But energy is not a function of time $E=h\nu$? | physics | 2017-04-20T07:57:25.920 |
[
{
"message": "So the Wood-Saxon density distribution for protons in a nucleus is given as follows:$$\\rho_p(r) = \\frac{\\rho_{p0}}{1+e^{[(r-R_0)/a]}}$$Here $r$ is the distance to the centre of the nucleus, and $a$ is the so called skin depth. $\\rho_{p0}$ is a constant such that the integral of the distributio... | Question about Woods-Saxon density distribution | physics | 2017-04-20T11:52:15.767 |
[
{
"message": "Here is my understanding:Non laser light must be passed through a single slit before being directed at double slits. This is to:1) make the light sufficiently monochromatic such that the double slits emit waves of the same frequency2) to make the light into a point source such that the double slit... | Why can bright and dark fringes form with white light? | physics | 2017-04-20T15:08:52.863 |
[
{
"message": "I am supposed to find the value of the redshift during photon decoupling when $\\Gamma=H$, where $\\Gamma=n_e \\sigma c$ is the rate of photon-electron scattering and $H$ is the Hubble parameter. I know that during photon decoupling the Universe is matter dominated, so I take $$H^2\\approx H_0^2 \... | How to find the density of electrons during the recombination era? | physics | 2017-04-20T16:49:04.180 |
[
{
"message": "Given a fluids viscosity, dynamic viscosity, initial velocity, initial pressure, and a pipes length and diameter as well as knowledge that it is vertical, is it possible to calculate the pressure drop for the fluid in the pipe? I've been trying to use the steady mechanical energy equation, but so ... | How to calculate pressure drop in vertical pipe? | physics | 2017-04-20T18:13:06.003 |
[
{
"message": "I have serious trouble understanding the concept of spontaneous symmetry breaking (in condensed matter specifically). Let's take time reversal in magnetic systems as an example. Ferromagnetism is said to spontaneously breaks time reversal symmetry. As I understand it, time reversal symmetry can be... | What is so special about spontaneous symmetry breaking? (time reversal example) | physics | 2017-04-20T20:57:14.183 |
[
{
"message": "I'm trying to work out the symmetry factor for a scattering inthe $\\phi^4$ theory. My initial and final states are:$\\left|i\\right> = \\left|p_1,p_2 \\right>$$\\left|f\\right> = \\left|p_3,p_4 \\right>$The expression for the amplitude to first order in $\\lambda$ is of the form:$$\\l... | Combinatoric factor in $\phi^4$-theory scattering | physics | 2017-04-20T21:53:11.363 |
[
{
"message": "I was looking at <a href=\"https://physics.stackexchange.com/a/40849/140964\">this answer on why <a href=\"https://en.wikipedia.org/wiki/Spectral_line\" rel=\"noreferrer\">absorption lines and emission lines don't cancel out: <blockquote> An experiment shining light on the material and looking at... | Why don't absorption and emission lines cancel out in our Sun? | physics | 2017-04-20T23:54:34.283 |
[
{
"message": "The Out-of-time-ordered correlator (OTOC) is defined as $\\langle[W(t),V(0)]^2\\rangle$, and can be considered as a new way to extract quantum chaos. However, the understanding of this special correlator is not clear. For a simple example, what the free fermion OTOC behaves? Both lattice or contin... | What is the Out-of-time-ordered correlator for free fermion system? | physics | 2017-04-21T04:28:19.130 |
[
{
"message": "I have the Hamiltonian:$$H(x,p)=\\frac{p^2}{2m}+\\frac{x^4}{4}$$When I find the critical points associatted with the system $\\dot{x}=\\frac{p}{m}$ and $\\dot{p}=-kx^3$, I find only one critical point in (x=0,p=0). Then I get the Jacobian matrix, evaluate it at this point and I get its eigenvalues... | Phase portrait Hamiltonian system | physics | 2017-04-21T10:41:15.423 |
[
{
"message": "What does happen if I push a piston in an adiabatic cylinder containing an ideal gas?According to Ideal Gas Equation:$$PV=nRT$$Is it possible to predict what's going to happen? Will Temperature and Pressure increase while Volume decreases?Do we have to control one Variable in all processes?",
... | What does happen if I push a piston in an adiabatic cylinder containing an ideal gas? | physics | 2017-04-21T16:54:40.583 |
[
{
"message": "What i'm struggling with is this question:Consider a spin S in an external magnetic field along the quantization axis so that the $|S_{z}>$ states are eigenstates with equally spaced eigenvalues E = $-h$$S_{z}$. For this Hamiltonian describe the time evolution of a spin-coherent state and rela... | Time evolution of a spin-coherent state | physics | 2017-04-21T20:15:44.623 |
[
{
"message": "There is <a href=\"https://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-structure-of-matter/protons-and-neutrons/\" rel=\"noreferrer\">a blog post by Matt Strassler about the structure of hadrons.He contrasts the \"conventional\" picture of hadrons shown below:<a href=\"htt... | What's the difference between a meson and a glueball? | physics | 2017-04-21T21:18:13.980 |
[
{
"message": "I make some calculations for double square potential well and I want the values to make sense for a real physical system. The energy is in eV. What would be a convenient unit of distance?On <a href=\"https://en.wikipedia.org/wiki/Electronvolt#Distance\" rel=\"nofollow noreferrer\">wikipedia one ca... | What units of distance should I use for square potential well? | physics | 2017-04-21T22:49:03.710 |
[
{
"message": "I am trying to do a Higgs triplet extension of the standard model but I don't know how to find the corresponding vacuum expectation value for the Higgs triplet. I read a paper where they found the expectation value for doublet to be $$<\\phi>_0 =\\frac{1}{\\sqrt{2}}\\Big{(}\\begin{matrix}0\\... | How to find vacuum expectation value of Higgs triplet? | physics | 2017-04-22T01:50:28.147 |
[
{
"message": "It says in my text book that einsteins photoelectric equation assumes the kinetic energy of a conduction electron can be considered negligible - this is confusing as everywhere else seems to say it's not the conduction electrons that are emmitted; it's the electrons in the atoms, and if it is the ... | Why can an electrons initial kinetic energy be considered negligible in the photoelectric effect? | physics | 2017-04-22T15:34:27.907 |
[
{
"message": "A telescope gives a clear view of a distant object when the angular displacement between the edges is at least $9.7 × 10^{-6} rad$. The Moon is approximately $3.8 × 10^5$ km from the Earth. Estimate the minimum diameter of a circular crater on the Moon's surface that can be seen using the telescop... | Angular displacement, minimum diameter of crater, and telescopes | physics | 2017-04-22T15:40:45.733 |
[
{
"message": "Let the electrical field inside the spherical shell be $E_1$ and outside be $E_2$, then by Gauss law, $E_2 - E_1 = 4\\pi \\sigma /k$, where $\\sigma$ is surface charge density of the spherical shell. Let the the volume charge density be $\\rho$ ranging from $x = 0$ to $x = x_0$ the thickness of th... | Electrostatic force on the spherical shell by the spherical shell | physics | 2017-04-22T18:16:57.810 |
[
{
"message": "On a tennis court I often have 20 – 50 tennis balls randomly scattered in a portion of the court. When gathering the balls I will occasionally kick one into the scatter. I am surprized that rarely does the kicked ball pass through the scatter without a collision. The successful passage of a ball t... | Collisions with randomly scattered objects | physics | 2017-04-22T23:26:47.770 |
[
{
"message": "Coulombs law finds force between two charged objects, but what is the force if only one of the objects is charged?",
"role": "user"
},
{
"message": "Theoretically, if the two objects are point particles, the force is zero as answered by Noiralef.For real objects, however, there will be... | Finding electrical force between a charged object and an uncharged object? | physics | 2017-04-23T07:56:01.073 |
[
{
"message": "Generally, electric fields can't penetrate plasmas, and this is known as debye shielding. But when I was thinking about the E cross B drift, this hit me.The average motion of a particle along the perpendicular to the magnetic field is zero. By this I mean't to say particles do not drift perpendicu... | Can electric fields penetrate a plasma in the presence of a magnetic field? | physics | 2017-04-23T10:39:23.560 |
[
{
"message": "In every textbook on particle physics that I've read, I encounter the following matrix when reading about matrix of wave functions for the baryon octet:$$\\left[\\begin{array}{ccc} \\frac{\\Sigma^0}{\\sqrt{2}} + \\frac{\\Lambda}{\\sqrt{6}} & \\Sigma^+ & P \\\\ \\Sigma^- & -\\frac{\\Sig... | How to Derive Baryon Octet Matrix? | physics | 2017-04-24T08:29:06.267 |
[
{
"message": "If you placed a disk and a half-sphere made of the same, partially reflective material at the same distance from the (point) light source (distance measured to centre of sphere and middle of a disk), which object would absorb more energy per given time?",
"role": "user"
},
{
"message":... | Half-sphere vs disk energy absorption | physics | 2017-04-24T10:29:42.423 |
[
{
"message": "I am studying the non dimensional heat equation for a finite rod, and have the quantity $$Q=-\\frac{\\partial \\theta}{\\partial x}$$ where $\\theta$ and $x$ are non dimensional temperature and distance respectively. I was wondering what this quantity means. Question 1: Is it heat flow in the posi... | What does heat flux mean? | physics | 2017-04-24T17:19:29.913 |
[
{
"message": "The Kubo formula for Hall conductance in the Quantum Hall Effect is given as $$\\sigma_{xy}=i \\hbar \\sum_{n \\neq 0}\\frac{\\langle{0}|J_y|n\\rangle \\langle n|J_x|0\\rangle - \\langle{0}|J_x|n\\rangle \\langle n|J_y|0\\rangle}{(E_n-E_0)^2}$$I have read (and understood) the derivation. However, ... | Interpretation of the Kubo formula for Hall conductance | physics | 2017-04-24T17:53:26.183 |
[
{
"message": "I have a question regarding a Derivation presented on the web page <a href=\"http://www.pas.rochester.edu/~stte/phy418S05/hw3.html\" rel=\"nofollow noreferrer\">http://www.pas.rochester.edu/~stte/phy418S05/hw3.html.The Problem is to calculate the Partition function for a (discrete) elastic string.... | Partition Function - Simpler computation by changing ensemble | physics | 2017-04-24T20:30:21.370 |
[
{
"message": "Is there a way to understand the underlying \"cause\" for observing (special) relativity? What is the structure/geometry that makes these observations make sense? I noticed that if all objects are required to move at the speed of light through a normal four dimensional euclidean space, this has es... | Underlying structure behind relativity? | physics | 2017-04-24T20:48:33.027 |
[
{
"message": "Is there a way to understand the underlying \"cause\" for observing (special) relativity? What is the structure/geometry that makes these observations make sense? I noticed that if all objects are required to move at the speed of light through a normal four dimensional euclidean space, this has es... | Underlying structure behind relativity? | physics | 2017-04-24T20:48:33.027 |
[
{
"message": "What I'm asking is, if an ideal cylindrical inductor/electromagnet is charged and then discharged, will the energy lost by charging the inductor/electromagnet be equal to the energy gained by discharging it or will some of it be lost to radiation? Based on what I know about magnetism, there should... | Could an ideal inductor lose energy to electromagnetic radiation when charging and discharging? | physics | 2017-04-25T05:39:10.343 |
[
{
"message": "Is it possible to create such a wall composed with inaudible sound waves that the other sounds are completely reflected when they touch it ? Like a super wall with no transmission through it but with sound waves.<br><br>Thank you !",
"role": "user"
},
{
"message": "At first blush, no. ... | Sound walls with sound waves | physics | 2017-04-25T12:38:09.020 |
[
{
"message": "Ref. 1 uses a notion of non-Heisenberg uncertainty relations (UP).The authors remark that \"because spins obey non-Heisenberg uncertainty relations, enables simultaneous precise knowledge of spin angle and spin amplitude.\"There are no experiments with revised limits of the standard UP.The standar... | Are There Experiments with Revised Limits of the non-Heisenberg Uncertainty Principle? | physics | 2017-04-26T07:21:33.630 |
[
{
"message": "<a href=\"https://en.wikipedia.org/wiki/Quadrupole_ion_trap\" rel=\"nofollow noreferrer\">Paul traps have been confusing me a lot recently. So sorry if there are too many questionsI know that Paul traps confine ions with the help of rapidly switching quadruple electric fields, I've heard that Paul... | Trying to understand Paul traps | physics | 2017-04-26T12:46:46.917 |
[
{
"message": "I have read different questions related to the atomic orbitals labelled with 2px and 2py present here, such as <a href=\"https://physics.stackexchange.com/questions/190726/what-is-the-difference-between-real-orbital-complex-orbital/329122#329122\">What is the difference between real orbital & ... | Atomic orbitals and complex wavefunction | physics | 2017-04-26T12:55:28.573 |
[
{
"message": "I have watched <a href=\"https://www.youtube.com/watch?v=Xo232kyTsO0\" rel=\"nofollow noreferrer\">PBS Space Time that gluons could be viewed as negative potential energy (tension between quarks) and that they actually are 99% of all the mass in protons and neutrons.Now the way I understand negati... | Where did all the negative potential energy in gluons went to? | physics | 2017-04-26T16:41:59.897 |
[
{
"message": "In Peskin p.282, it is said \"The general functional integral formula (9.12) derived in the last section holds for any quantum system, so it should hold for a quantum field theory.\" (9.12) is the formula<br>$U(q_a,q_b,T)=(\\prod_i\\int Dq(t)Dp(t))\\exp[i\\int_0^T dt(\\sum_ip^i\\dot{q}^i-H(q,p)]$I... | Paradox in derivation of path integral of quantum fields | physics | 2017-04-27T07:10:00.343 |
[
{
"message": "I was reading some papers on astrophysics, and in several of them, I've encountered velocity being used as distance. Or more precisely, distance being in dimensions of distance over time. For example, a paper referred to a group of galaxies at \"roughly $2000\\:\\mathrm{km\\:s^{-1}}$ in distance.\... | What is "velocity distance" in astrophysics? | physics | 2017-04-27T13:56:05.213 |
[
{
"message": "$$\\psi(x,t) = \\int_{-\\infty}^{\\infty} A(k)e^{i(kx-w(k)t)} \\mathrm{d}k$$Also, what properties of this equation will tell me whether or not this wave is going to spread over time?",
"role": "user"
},
{
"message": "That's a general solution for a wave packet.1) A(k) is the spatial Fo... | How to tell if wavepacket is nonstationary vs. stationary? | physics | 2017-04-27T21:07:17.933 |
[
{
"message": "What is the mechanism of cold neutron radiative capture by proton? I have seen some experimental papers on studies of parity violation via this reaction, but I haven't seen a fundamental description of the process or references on one. The old nuclear theory books seem to either omit this topic co... | Cold neutron radiative capture by proton | physics | 2017-04-27T21:18:29.183 |
[
{
"message": "The answer is C, but why? At first I thought it was B because the springs would shake the block causing it to produce a wave and as more time has elapsed there would have been more time for friction to act on the block making the block slowly returning to equilibrium. My second possible reasoning ... | How does a spring generate a wave? AP Physics 1 | physics | 2017-04-28T05:02:20.807 |
[
{
"message": "My current understanding of the topic does not allow me to answer this question.Also, by 'object' I mean a theoretical massless macroscopic object (if we assume such an object is possible, and if such an assumption is absurd, then let the object be a group of massless particles).Since at a speed o... | Is speed essentially infinite for a massless object moving at $c$? | physics | 2017-04-28T06:32:53.113 |
[
{
"message": "At a very basic level, fusion can occur when the electrostatic repulsion between nuclei is overcome and they approach close enough for the strong force to come into play. Thus, the easiest reactions would occur in nuclei with the lowest electrical charge relative to their nucleon count.So that bei... | Why is D-T fusion easier than T-T? | physics | 2017-04-28T14:46:32.330 |
[
{
"message": "Consider an object say O (which is a rigid body having appreciable dimension wrt its orbit) is rotating about a fixed point C (and it is not spinning about its axis through centre of mass) at centre of circular orbit then At first guess we would assume that the body is just translating and all par... | What kind of motion is orbital revolution it most definitely cannot be pure rotation as no particle of body is fixed? | physics | 2017-04-29T08:25:52.847 |
[
{
"message": "Question :two railroad boxcars weighing $50,000$ N each are approaching one another at $5$m/s and $7$ m/s. After they collide and couple together, how fast will thecombination be moving and in which direction?From the problem I have the following setup:<a href=\"https://i.stack.imgur.com/SGUCV.png... | Linear momentum, colliding bodies, whether they move in the same direction after collision | physics | 2017-04-29T15:23:46.887 |
[
{
"message": "What is meant when it is said a CCD's response is nonlinear? Does it mean the value of a pixel of the camera is not proportional to the number of received photons? Does it involve saturation? What factor expresses this?",
"role": "user"
},
{
"message": "Yes, non-linear simply means the... | Nonlinear Response of CCD camera | physics | 2017-04-29T16:24:31.117 |
[
{
"message": "From the method of images we know that the potential everywhere above a grounded plate with a point charge above it is equal to$$ V(x,y,z) = (\\frac{q}{4 \\pi \\epsilon_0})[ \\frac{1}{\\sqrt{x^2 + y^2 + (z-d)^2}} - \\frac{1}{\\sqrt{x^2 + y^2 + (z+d)^2}}] $$$$ = (\\frac{q}{4 \\pi \\epsilon_0})[ \\... | Point charge above infinite plate - with Legendre Polynomials | physics | 2017-04-29T23:32:41.680 |
[
{
"message": "Suppose I have a ideal gas mixture consisting of two different types of ideal gases, say $A$ and $B$, in a container with volume $V_{tot}$. There are $N_A$ particles of gas $A$ and $N_B$ particles of gas $B$. The temperature and pressure of the mixture are denotes by $T$ and $P$. Can I still use t... | Confused about ideal gas law with two types of gases | physics | 2017-04-30T07:35:40.863 |
[
{
"message": "I have an axially magnetized neodymium magnet of diameter $d$ and height $h$. The material is N42. I would like to derive a formula for the pull force.This calculator does it: <a href=\"https://www.kjmagnetics.com/calculator.asp\" rel=\"nofollow noreferrer\">https://www.kjmagnetics.com/calculator.... | What is the formula for the pull force of a cylindrical magnet | physics | 2017-04-30T13:12:06.727 |
[
{
"message": "The electromagnet spectrum looks to be continuous, yet energy is discrete. Shouldn't one see evidence of the electron's \"quantum leap\"? What's going on?<a href=\"https://i.stack.imgur.com/uTHGfm.jpg\" rel=\"nofollow noreferrer\"> Moderator, please size my photo. Thank you.",
"role": "user"
... | Why do I not see evidence of discrete energy in the spectrum? | physics | 2017-04-30T15:40:43.347 |
[
{
"message": "I am studying introductory electricity and magnetism, and this is a conceptual question.For an infinite conducting sheet, any excess charge is localized onto one side. There is no electric field in the interior of the surface or the other side. The reasoning, as I understand it, is that any such f... | Infinite Conducting sheet | physics | 2017-05-01T03:10:59.977 |
[
{
"message": "Can a system without any interaction with other system be a non-equilibrium system; or is it that gain and loss is always needed for non-equilibrium?",
"role": "user"
},
{
"message": "Yes, of course. The simplest way to see this is to consider a system with non-equilibrium initial cond... | Can a closed system be a non-equilibrium system? | physics | 2017-05-01T08:45:19.797 |
[
{
"message": "Friction arises as an effective macroscopic force, unlike the four fundamental interactions in nature which are there at the microscopic level. How can we understand, the appearance of friction as a dissipative force originating from the fundamental interactions between atoms or molecules? In part... | How does friction and its velocity dependence arise from microsocpic interactions? | physics | 2017-05-01T16:12:53.927 |
[
{
"message": "Consider a box. How to open it by creating a pressure in the box, without contact?For example, can I open it by a sound bomb?",
"role": "user"
},
{
"message": "A <a href=\"https://en.wikipedia.org/wiki/Blast_wave\" rel=\"nofollow noreferrer\">blast wave of sufficient strength will be f... | How to open a box? | physics | 2017-05-02T00:18:55.737 |
[
{
"message": "I am trying to derive the result of the TKNN formula but am experiencing difficulty in deriving the Kubo formula. The Kubo formula used in the TKNN paper is,$$ \\sigma_{xy}= \\frac{ie^2}{\\hbar} \\sum_{E^a < E_F < E^b} \\frac{\\langle a|v_x|b \\rangle \\langle b|v_y|a \\rangle - \\langle a|v... | Derivation of Kubo Formula for Hall Conductance | physics | 2017-05-02T11:09:33.813 |
[
{
"message": "there is the experiment called coin drop. you have a glass and a coin on top of a surface such as a paper. so basically when you move the paper slowly the coin remains on it but when you move it really fast the coin drops into the glass. I asked my teacher why is that and he said that it is becaus... | The coin drop experiment | physics | 2017-05-02T18:31:30.680 |
[
{
"message": "On page 257 of Griffiths' Quantum book, he says \"Typically, the perturbation will break the degeneracy: As we increase $\\lambda$, the common unperturbed energy $E^0$ splits into two. Going the other direction, when we turn off the perturbation, the \"upper\" state reduces down to one linear comb... | How do we know/prove that a perturbation splits degenerate states into orthogonal linear combinations? | physics | 2017-05-02T18:46:04.987 |
[
{
"message": "On page 257 of Griffiths' Quantum book, he says \"Typically, the perturbation will break the degeneracy: As we increase $\\lambda$, the common unperturbed energy $E^0$ splits into two. Going the other direction, when we turn off the perturbation, the \"upper\" state reduces down to one linear comb... | How do we know/prove that a perturbation splits degenerate states into orthogonal linear combinations? | physics | 2017-05-02T18:46:04.987 |
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