question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>Creating a beam of antiprotons allows to create antineutrons by charge exchange. How does this exchange work?
The question pops up after the question "<a href="http://physics.stackexchange.com/questions/134174/is-there-a-strong-evidence-of-antineutron-existance/134175?noredirect=1#comment274838_134175">Is there a st... | 4,912 |
<p>I thought I knew how to use calculus of variations, but then I started thinking about the problem of a rotating liquid and it confused me a great deal. It would be nice to hear your thoughts on the problem.</p>
<p>Suppose we have a liquid in a spinning cylinder in an equilibrium (i.e. the liquid is still in the rot... | 4,913 |
<p>A chain of some mass, forming a circle, is slipped on a smooth cone.
If we consider an infinitesimally small section of the chain, a component of gravity will try to accelerate it along the surface of the cone. So there must be some tension in the string that prevents the acceleration. What will be the direction of ... | 4,914 |
<p>How does the number of blades in a fan affect the flux of air? I read that 3 blades are the best option but some companies uses more blades because there's a misconception among people that more blades generates more air. </p> | 4,915 |
<p>Supposing it's possible to see some distant galaxies with an earth telescope, then, at the tip of the telescope lens there are photons comming from the distant galaxy...</p>
<p>So, if I extend my hand in a dark night without visible moon, and far from city lights, photons from distant galaxies are in my hand skin..... | 4,916 |
<p>I'm given a wave propagation in an anisotropic medium with the following properties:</p>
<p>$\epsilon=\left[\begin{array}{ccc} \epsilon_{11} & 0 & 0 \\
\epsilon_{21} & \epsilon_{22} & \epsilon_{23} \\
0 & 0 & \epsilon_{33} \end{array}\right] $ </p>
<p>$\mu=\left[\begin{array}{ccc} \mu_{... | 4,917 |
<p>Bear with me while I try to explain exactly what the question is. The question <a href="http://physics.stackexchange.com/questions/122392/can-a-curvature-in-time-and-not-space-cause-acceleration">Can a curvature in time (and not space) cause acceleration?</a> is imagining a coordinate system in which the curvature i... | 4,918 |
<p>I am just curious about the formalism of basic Quantum Mechanics. Lets take for instance the system of a spin-$\frac{1}{2}$ particle. The state of the particle is described by a vector in an abstract Hilbert space that is two dimensional (say $\mathcal{H}$). The set of Endomorphisms on $\mathcal{H}$ form a group (wh... | 4,919 |
<p>In the one-dimensional spin-$\frac12$ XXZ Heisenberg model,
$$H=J\sum_i{S_i^x S_{i+1}^x + S_i^y S_{i+1}^y+\Delta S_i^z S_{i+1}^z},$$
with $J>0$. There are two transition points:</p>
<ul>
<li>$\Delta=1$</li>
<li>$\Delta=-1$</li>
</ul>
<p>The transition at $\Delta=1$ is of BKT type. What about the transition a... | 4,920 |
<p>At the back of my mind I know they should be equal, but mathematically, how are the two $\Delta \phi$ angles equal?
<img src="http://i.stack.imgur.com/qIxBs.png" alt="Angles Image"></p>
<p>The only explanation present in the text is that, "both velocities are perpendicular to the radii vectors," but I don't see how... | 4,921 |
<p>Under light from the sun, a red object will scatter the red component of light, and absorb all others. Hence, the human eye perceives it as "red". White objects scatter all wavelengths of light.</p>
<p>Yesterday I bought an orange light bulb. Under its light, orange/reddish carrots look white. Why is that? A "white... | 4,922 |
<p>One way of detecting exoplanets orbiting around a star is the <a href="http://en.wikipedia.org/wiki/Methods_of_detecting_exoplanets#Radial_velocity" rel="nofollow">Radial velocity method</a>.</p>
<p>Can this be used to detect multiple planets? Wouldn't the star orbit the center of mass of the whole system with a co... | 4,923 |
<p>The following is an old question from an exam in a Physics $2$ course
I am taking, I have tried to solve the question and after I thought
I got the answer I looked at the solution and saw it isn't correct.</p>
<p>The solution explains what the answer is, but doesn't really explains
the facts used.</p>
<blockquote>... | 4,924 |
<p>Say, I'm amplifying a signal using a device with gain bandwidth, ΔG Hz, which is unknown.</p>
<p>My source signal which is being amplified is known to have a bandwidth of X Hz, and the amplified output signal has a measured bandwidth of Y Hz.</p>
<p>Is it possible to process the input and output signal to find the... | 4,925 |
<p>Ok I am hoping to apply this answer to a piece of software, but it uses physics to work out the result so I require some help in that department. </p>
<p>I will attempt to explain this the best I can.</p>
<p>I need to work out the continual position of a scrolling list. If you were to flick the list it would conti... | 4,926 |
<p>I am slightly getting confused on the following issue:</p>
<p>When performing double-slit experiment of electrons, a screen allows the matter waves to be detected as particles. And as we all know that everything around us in fact consists of matter waves, the screen must also be formed of matter waves.</p>
<p>Then... | 4,927 |
<p>Fastest baseball pitch ever recorded was in 1974 at a speed of 100.9 miles per hour.</p>
<p>Does this mean that the pitcher's hand was also traveling at that speed or just the ball?</p>
<p>Is it physically possible to move hand/leg at that speed?</p>
<p>I'm asking this because basically pitcher's hand was moving ... | 4,928 |
<p>I think this is supposed to be a simple problem but I am having a hang up converting it to a one-body problem. It's one-dimensional. +q and -q a distance d apart, held stationary then let go at t=0. The potential is V(x)=kq^2/x. If I turn it into a one body problem, then m-->m/2, but how do i interpret the new x? Bo... | 4,929 |
<p>So when two boxes are connected together, and force is applied, two boxes move with the same acceleration. (assuming force is constant.) My question is, how are forces between two boxes get cancelled out? When force is applied to the first box, it would exert force into the second box which pushes the first box with... | 4,930 |
<p>According to special relativity, time starts to slow down as we increase our speed and eventually stops once we get to the speed of light. By that logic, photons don't age in a vacuum state as, to us, the time stops for them. However, in a medium, their speed decreases, that means time is 'stationary'. Does that mea... | 4,931 |
<p>Whenever one needs to calculate correlation functions in QFT using perturbations one encounters the following expression:</p>
<p>$\langle 0| some\ operators \times \exp(iS_{(t)}) |0\rangle$</p>
<p>where, depending on the textbook S is either (up to a sign)</p>
<ol>
<li><p>$\int \mathcal{L}dt$ where $\mathcal{L}$ ... | 4,932 |
<p>The Randall-Sundrum extra dimension scenario had been one of the most extensively studied class of theories. This offered a solution to the hierarchy problem. However, if this picture is not supported by the LHC, will it become completely defunct? What about theories like little higgs, composite higgs, technicolor, ... | 4,933 |
<p>Imagine I have room that is very hot and it is colder outside. I want to cool it down using a fan.</p>
<h2>Scenario 1</h2>
<p>There is only one door. I have one fan.</p>
<p>Where should I put it and which way should it blow?</p>
<p><img src="http://i.stack.imgur.com/540TE.png" alt="Room with a door"></p>
<h2>Sc... | 4,934 |
<p>For a bipartite quantum system evolving under some master equation, is the time derivative of the reduced density matrix equal to the partial trace of the time derivative of the matrix? </p>
<p>In other words, is the following true:</p>
<p>$\dot{\rho}_{A} = Tr_B(\dot{\rho}_{AB})$</p>
<p>(Where $\rho_A = Tr_B(\rho... | 4,935 |
<p>What is a good definition on Space, <a href="http://physics.stackexchange.com/q/17056/2451">Time</a> and the most specific topic "<a href="http://en.wikipedia.org/wiki/Spacetime" rel="nofollow">Spacetime</a>"? Because someone told me that spacetime is the foundation of the entire universe?</p>
<p>And also, Is it po... | 4,936 |
<p>The <strong>ADM mass</strong> is expressed in terms of the initial data as a surface integral over a surface $S$ at spatial infinity:
$$M:=-\frac{1}{8\pi}\lim_{r\to \infty}\int_S(k-k_0)\sqrt{\sigma}dS$$
where $\sigma_{ij}$ is the induced metric on $S$, $k=\sigma^{ij}k_{ij}$ is the trace of the extrinsic curvature of... | 4,937 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/10309/conservation-law-of-energy-and-big-bang">Conservation law of energy and Big Bang?</a> </p>
</blockquote>
<p>If energy can't be created or destroyed then how did the big bang create energy? and if e... | 166 |
<p>Is it possible that a false vacuum bubble to nucleate into our universe rather than a true vacuum one ? If yes,it will expand at speed of light within our spacetime or what ?</p> | 4,938 |
<p>Let's consider a bubble nucleation phase transition between different vacua via quantum tunnelling .For my understanding a particle must penetrate the potential barrier and find herself in an another energy state over the barrier. But this doesn't mean that the parent vacuum loses the particle ?This doesn't violate ... | 4,939 |
<p>On a question from my book:</p>
<blockquote>
<p>A long straight wire with a circular cross section of radius $R$ carries a current $I$. Assume the current density is not constant over the cross section of the wire, but rather varies as $J=\alpha r$ where $\alpha$ is a constant. Given $I, R$ </p>
<p>Find $\al... | 4,940 |
<p>It was a few days ago, and there was a very heavy storm(currents were flowing beside the sidewalks as normal). I became intrigued by a thin film of gasoline that got caught in one of the currents. The visible colors of course changed by my angle of incidence, yet because there was a current, the thickness of the fil... | 4,941 |
<p>I'm stuck on a problem of two satellites going towards each other. The mass of the first satellite is 400kg and the mass of the second satellite is 100kg. The altitude of the satellites is 1000km. I want to know if once the satellites collide, will they continue in orbit or will they crash and burn into the Earth? <... | 4,942 |
<p>I'm trying to make a simple conceptual map regarding some of the things in the title as they pertain to quantum mechanics and or quantum field theory, and I'm finding that I'm a little perplexed about a couple of items. Let me summarize a few things I have as being true, and then state what I don't understand.</p>
... | 4,943 |
<p>I have a $2D$ fluid parcel with coordinates $(0.5,-0.5), (-0.5,-0.5), (0.5,0.5)$ and $(-0.5,0.5)$ and this parcel is deformed by a steady flow field of $u=ay$ and $v=0$, defined on the basis ${(1,0), (0,1)}$. I tried to calculate the velocity gradient tensor $\tau_{ij}$ given by the matrix
$ \left( \begin{array}{cc... | 4,944 |
<p>I've been directed to a few articles, and I am sure there is a related post, but can someone explain the procedure by which we can view classic electromagnetism through quantum mechanics? Indeed we need to be able to look at any field as an ensemble of particles (photons), but how can we develop classic field theory... | 167 |
<p>Below is an image showing transducer A transmitting a signal with an amplitude of 3000mV, I am trying to calculate the amplitude of the signal received by transducer B in mV,
I understand that there are dB losses at each of the acoustic interference (1 to 5), </p>
<ol>
<li><p>Which of the two formulae (given below)... | 4,945 |
<p>Some background:</p>
<p>I'm majoring in Electronics and Instrumentation engineering, but I want to pursue theoretical physics. I'm currently In my second year of undergrad engineering. I attend some physics classes in the weekends and I've learnt classical mechanics (from John R. Taylor's book predominantly, with o... | 4,946 |
<p>Lets say you have a cylinder of length L, radius R, and mass M. How fast will it accelerate a mass of mass M2 that is entering the "throat" of the cylinder, considering the effects of <a href="https://en.wikipedia.org/wiki/Gravitoelectromagnetism" rel="nofollow">gravitoelectromagnetism</a>?</p>
<p>By Gravitoelectro... | 457 |
<p>Assume this question:</p>
<blockquote>
<p>Three events A, B, C are seen by observer O to occur in the order ABC. Another observer O$^\prime$ sees the events to occur in the order CBA. Is it possible that a third observer sees the events in the order ACB?</p>
</blockquote>
<p>I could draw spacetime diagram for th... | 4,947 |
<p>For a project I'm working on I'm using an accelerometer which measures acceleration in 3 directions, x, y and z.</p>
<p>My question is: How can I calculate the total acceleration in a certain direction from these 3 values?</p>
<p>Considering this simple graph layout: <img src="http://i.stack.imgur.com/UX9S8.png" a... | 4,948 |
<p>A potential that depends on time is usually solved using the time dependent perturbation theory in standard undergraduate textbooks in quantum mechanics. The reason usually mentioned is that time dependent potentials cannot be solved using separation of variables. </p>
<p>Is this the only reason why it has to be so... | 4,949 |
<p>I have this continuum version $$ H_{R}=\int dx\psi^{\dagger}(x)(\frac{p^{2}}{2}+V)\psi(x) $$ with $V$ as constant potential.</p>
<p>Is it always justified to go from this to $$ \sum_{i}c_{i}^{ \dagger }\left[c_{i+1}+c_{i-1}-2c_{i}\right] +V \sum_{i}c_{i}^{ \dagger }c_{i} $$
using the finite difference form of the o... | 4,950 |
<p>I report to you an interesting excerpt from my Physics book.
It is an Italian version, so I apologize in advance, as I'm sure I won't give proper justice to its beauty in the translation as the authors would have done.</p>
<p>Talking about </p>
<blockquote>
<p>There is a profound theoretical connection between ... | 4,951 |
<p>Can one explain the relativistic energy transformation formula:</p>
<p>$$E = \gamma\ E',$$</p>
<p>where the primed frame has a velocity $v$ relative to the unprimed frame, in terms of relativistic time dilation and the quantum relation $E=h\nu$?</p>
<p>I imagine a pair of observers, A and B, initially at rest, ea... | 4,952 |
<p>I have calculated the dipole transition elements of electronic states $\langle a|D_1^m|b \rangle$ following the book of Cohen-Tannoudji (Complement $E_X$) and tried then to calculate from that the Rabi frequency $$\Omega_{a\to b}=\frac{1}{2\hbar}E_m \langle a|D_1^m|b \rangle.$$
But what is the direction of the E-fi... | 4,953 |
<p>Using the <a href="http://books.google.ie/books?id=ecS5DKstwREC&pg=PA196&dq=%22engineers%20and%20physicists%20who%20use%20the%20Laplacian%22&hl=en&sa=X&ei=7f96UqXOG8PQ7AbG7YG4Ag&ved=0CDEQ6AEwAA#v=onepage&q=%22engineers%20and%20physicists%20who%20use%20the%20Laplacian%22&f=false">intui... | 4,954 |
<p>According to the <a href="http://en.wikipedia.org/wiki/Haag%E2%80%93Lopuszanski%E2%80%93Sohnius_theorem">Haag-Lopuszanski-Sohnius theorem</a> the most general symmetry that a consistent 4 dimensional field theory can enjoy is <a href="http://en.wikipedia.org/wiki/Supersymmetry">supersymmery</a>, seen as an extension... | 4,955 |
<p>A charged particle moving in a magnetic field experiences a Lorentz force $F=qv\times B$. A charged particle in a electric field experiences a force given by Coulomb's inverse square law. </p>
<p>But for a magnet we have what seems to be adhoc ways to calculate how the magnet will rotate.
In the above case we spea... | 4,956 |
<p>I recently got confused (and slightly annoyed by the lack of technical details) when reading a popular <a href="http://www.scientificamerican.com/article.cfm?id=dark-worlds" rel="nofollow">article</a> (authored by Jonathan Feng and Mark Trodden) introducing the concept of super WIMPs.</p>
<p>The article characteriz... | 4,957 |
<p>In the letter of introduction to Einstein's 1916 paper on General Relativity, he writes, "The mathematical tool sthat are necessary for general relativity were readily available in the 'absolute different calculus,' which is based upon the research on non-Euclidean manifolds by Gauss, Riemann, and Christoffel, and w... | 4,958 |
<p>Referencing this news article:
<a href="http://www.smh.com.au/technology/sci-tech/cosmic-burst-in-far-away-galaxy-puzzles-nasa-20110408-1d6kz.html" rel="nofollow">http://www.smh.com.au/technology/sci-tech/cosmic-burst-in-far-away-galaxy-puzzles-nasa-20110408-1d6kz.html</a></p>
<p>It also references an event id:<br>... | 4,959 |
<p>Can someone explain why the rotation matrix is a unitary, specifically orthogonal, operator?</p> | 4,960 |
<p>Who is the author of the term "Coulomb logarithm"? In fact, Coulomb logarithm was computed by Langmuir in his paper of 1928 where the term "plasma" was introduced into physics, but the term "Coulomb logarithm" seemed to appear later. The earliest reference I found is the paper <a href="http://www.fnti.kiae.ru/conten... | 4,961 |
<p>I have read through the wikipedia page and several lecture notes/arxiv papers from my google search (and several related P.SE questions), but I'm still hopelessly confused.</p>
<ol>
<li><p>Consider a 'classical Schrodinger field in a box' problem. Since the field evolves just like a normal wavefunction, I could sti... | 4,962 |
<p>For those spin liquids with <em>SU(2) spin-rotation symmetry</em> <strong>or</strong> <em>time-reversal(TR) symmetry</em> , the Spin Density Wave (SDW) order parameters are always zero, say $\left \langle \mathbf{S}_i \right \rangle=\mathbf{0}$, due to the spin-rotation symmetry or TR symmetry.</p>
<p>But if a spin... | 4,963 |
<p>Leslie Ballentine develops in QM: A Modern Development an interpretation based on the ensemble interpretation, and responds to most criticisms. </p>
<p>My question: what criticisms still exist against this interpretation such that it is not recognized as the standard interpretation within the physics community? </p... | 4,964 |
<p>I am trying to understand the balance of energy -law from continuum mechanics, fourth law <a href="http://en.wikipedia.org/wiki/Continuum_mechanics#Balance_laws" rel="nofollow">here</a>. Could someone break this a bit to help me understand it? From chemistry, I can recall $$dU = \partial Q + \partial W$$ where $U$ i... | 4,965 |
<p>Can any one suggest a good reference for studying renormalization of disjoint, nested and overlapping divergences in Feynman diagrams (for example, $\Phi^4$ theory)?</p> | 168 |
<p>I have a problem with the transition from quantum relativistic wave equations (specifically Klein-Gordon equation) to QFT, since a lot of assumptions seem implicit. For example I have a problem with the time evolution operator, which is crucial on deriving the perturbative expansion $-$ the main tool in QFT I believ... | 4,966 |
<p>In Griffiths' electrodynamics book, he uses the equation,
$$\nabla^2\mathbf{A}=-\mu_0 \mathbf{J},$$
to state that
$$\mathbf{A}(\mathbf{r}) = \frac{\mu_0}{4\pi}\int\frac{\mathbf{J}(\mathbf{r}')}{|\mathbf{r}'-\mathbf{r}|}\mathrm{d}\tau'.$$
This is, of course, justified by the fact that each cartesian component of $\ma... | 4,967 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/4669/what-are-the-most-important-discoveries-breakthroughs-in-physics-recently">What are the most important discoveries/breakthroughs in physics recently?</a> </p>
</blockquote>
<p>The last two decades h... | 169 |
<p>If we would hypothetically be exactly on the event horizon, we should see our own back, because of the circular motion of photons on the event horizon, right?</p>
<p>But what would be the image size, or $-$ asking differently $-$ how far away, would our back seem to be? Would it be magnified or minified, when compa... | 4,968 |
<p>How would I go about showing:</p>
<p>$$\hat{A}^{\dagger} + \hat{B}^{\dagger} = \left( \hat{A} + \hat{B} \right) ^{\dagger}$$</p> | 4,969 |
<p>In quantum physics we've defined:
$$ \psi (x) = \sqrt{ \dfrac{1}{2 \pi \hbar} } \int^{ \infty }_{-\infty } \phi (p) \exp \left( i \dfrac{px}{ \hbar} \right) dp $$
Now,
$$a(k) \equiv \sqrt{ \hbar } \phi (p)\quad {\rm and}\quad k = \dfrac{p}{ \hbar } $$
Where,
$$ a(k) = \left\{ \begin{array}{cccc} 0 & k < - ... | 4,970 |
<p>I understand that a voltmeter is used for measuring potential electrical difference, but how exactly should said voltmeter be connected with the resistor in circuit? </p> | 4,971 |
<p>During Hawking's radiation, a virtual particle with negative energy and mass (from pair of particle and antiparticle) fall into black hole and its real partner having positive energy escape from vicinity of black hole. And it <em>appears</em> to have been emitted from black hole. <em>Since these pair of particles we... | 4,972 |
<p>What is the direction is the magnetic force vectors pointing from a coil of wire that has current running through it?</p>
<p><a href="http://www.ndt-ed.org/EducationResources/CommunityCollege/MagParticle/Graphics/coil1.gif" rel="nofollow">http://www.ndt-ed.org/EducationResources/CommunityCollege/MagParticle/Graphic... | 368 |
<p>In the case of dispersion relation of silicon having crystal plane orientation 111; what is the <a href="http://en.wikipedia.org/wiki/Sellmeier_equation" rel="nofollow">Sellmeier's equation</a> for refractive index $n$ of silicon orientation 111 & what it's extinction coefficient $K$?</p> | 4,973 |
<p>I am trying to teach myself about electricity and magnetism and I have a few questions about <a href="http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity" rel="nofollow">resistance</a>. How does resistance of say a long wire compare to that of a a short wire? what about thick and thin? </p> | 4,974 |
<p>How do I calculate the <a href="http://en.wikipedia.org/wiki/Power_%28physics%29" rel="nofollow">power</a> of a lightbulb? I have values but I don't know the equation to use. </p> | 4,975 |
<p><strong>Question</strong></p>
<p><img src="http://i.stack.imgur.com/9JcHo.png" alt="http://i.imgur.com/ALUdyoB.png"></p>
<p>Create a set-up, as shown in the Figure, consisting of two mirror tiles (A and B)
and a bird face, facing to the right . Make sure the two mirrors are perpendicular to the table and parallel ... | 4,976 |
<p>The rear wheels of a car always face in the direction the car is moving. The front wheels are able to turn left or right and thus can point in the direction the car is moving towards. What I don't understand is how a car can turn with all four wheels rotating (not skidding). That is, how is it possible that the f... | 4,977 |
<p>Why <a href="http://en.wikipedia.org/wiki/Fermion_field" rel="nofollow">fermion field</a> is treated as anti-commuting and <a href="http://en.wikipedia.org/wiki/Boson" rel="nofollow">boson</a> field as truly classical in standard model?</p> | 4,978 |
<p>What is the total amount of energy in the universe? is there the same amount of energy as negative energy, cancelling each other out? Or is it something different?</p> | 27 |
<p>The one-form
$$\theta=\sum_i p_i\, \text dq^i$$
is a central object in hamiltonian mechanics. It has a bunch of applications: $\omega=\text d\theta$ is the symplectic structure on phase space, $S=\int\theta$ is the classical action, and so on and so forth. It is associated with the names Liouville one-form, Poincaré... | 4,979 |
<p>I always thought about symplectic forms as elements of areas in little subspaces because of the Darboux theorem, however I cannot get the physical intuition for it and for the hamiltonian vector field. </p>
<p>To simplify things, let's consider the configuration space $TQ$, we know that $T^{*}Q$ always have a sympl... | 4,980 |
<p>The following is the problem that I am working on.</p>
<blockquote>
<p>A bullet of $.01\: \mathrm{kg}$ is shot into a block of mass $.89\: \mathrm{kg}$ that is hanging from the ceiling. After the bullet has been caught in the block, it swings and rises $.40\: \mathrm{m}$ from its initial height. Find the initial ... | 4,981 |
<p>I read a book on the wave property of light where the author mentioned that the electric field, instead of magnetic field, dominates the light property. I don't understand why.</p>
<p>In Maxwell's theory, a light field has an electric and magnetic field at the same time and they are perpendicular. Also, in some boo... | 4,982 |
<p>Which properties are sufficient evidence for a material to be not superconducting?
I am looking for a set of statements like</p>
<blockquote>
<p>If the material is semiconducting, it is not superconducting</p>
</blockquote>
<p>Edit:
I am not looking for a definition of superconductivity, or for introductional l... | 4,983 |
<p>How can we charge a metal electrode with large charges ? When i saw a video about measuring a charge using a visiostat on a balloon , the charge was 0.6 nano-coulomb. Is the charge of 1 coulomb unachievable? </p> | 4,984 |
<p>Let us say that I am sitting in a room with all the drapes open. Bright sunlight is coming through the window. The whole room is brilliantly lighted. I will not be able to see the dust particles suspended in air.</p>
<p>Now, if I draw the drapes close, keeping a small slit open, allowing only a beam of sunlight to ... | 4,985 |
<p>My question is simple. Green light is more similar to red light than violet, then why is violet reddish and green not? in the language of frequencies and wavelengths, red and violet should contrast each other. Then why do they don't? </p> | 170 |
<p>Fundamental interactions, such as electromagnetism, the strong force, the weak force, and possibly gravitation, all have something in common: They can be described in terms of relativistic quantum fields, and are clearly the results of interactions between two different kinds of fields. For example, with an electro... | 4,986 |
<p>Imagine I have a solenoid connected to a power supply. Solenoid produces an electromagnetic field. Now I take a permanent magnet and place it inside the solenoid. How will the magnet align itself (assuming there is no gravity) inside the solenoid and will it rotate itself around the central axis "aligning" itself?</... | 4,987 |
<p>How does a universal battery charger, such as <a href="http://rads.stackoverflow.com/amzn/click/B002XY5F6A" rel="nofollow">this one</a> work, i.e. how does it know what voltage, current and polarity is appropriate for the battery inserted? Do batteries have some form of protocol to tell the charger these parameters?... | 4,988 |
<p>First I want to consider an example of 1D motion. Lagrange equation:</p>
<p>$$ \frac{d}{dt} \frac{\partial L}{\partial \dot x} - \frac{\partial L}{\partial x} = 0 $$</p>
<p>If we transform $ L \rightarrow L+a $ with $a$ a is constant, the equation of motion remains unchanged. This is global symmetry.</p>
<p>To ob... | 4,989 |
<p>QFT is a nonlocal unitary transformation and so can generate entanglement in a system. It means a separable pure state can be converted into an entangled pure state. Now since the presence of entanglement can be witnessed via an increase in the entropy of the subsystems. Since all the subsystems witness a positive e... | 4,990 |
<p>Let's say there is a dielectric ring of charge with radius $a$ and charge $q_1$. I could calculate the electrostatic force applied on a point charge with charge $q_2$ and which is collinear with the centre of the ring with these equations(the distance between ring and point charge is $r$ and the distance between the... | 4,991 |
<p>I was given this worksheet from my teacher and well im finding it really tough so far ..
the question below is just crushing my skull .. so i would appreciate it if you guys would guide me through it</p>
<blockquote>
<p>A particle projected from ground takes time $t_1$ to reach $\frac{15}{16} H$ and time $t_2$ to... | 4,992 |
<p>Why is geometric optics the low wavelength limit of the wave theory of light? I can't seem to grasp why either a low or high wavelength limit would be necessary.</p> | 171 |
<p>If we have a one-loop diagram in $\phi ^ 3$ scalar field theory with $n$ external lines, then what is its symmetry factor?</p>
<p><img src="http://i.stack.imgur.com/ssYJ7.jpg" alt="enter image description here"></p>
<p>I have drawn the diagram I am looking for, but instead of $6$ external lines, I want the diagram... | 172 |
<p>In the classical description of <a href="http://en.wikipedia.org/wiki/Raman_scattering" rel="nofollow">Raman effect</a> the object of study is the electric polarizability of the system.
Since I'm interested in learning the quantum description of the Raman effect and in Bernath's "Spectra of atoms and molecules" is s... | 4,993 |
<p>Taking this post: <a href="http://physics.stackexchange.com/a/71870/44176">"Is there a proof of existence of time?"</a>, as a starting point. Therein was mentioned that there is confusion between:</p>
<p>"<em>time</em>" and "<em>flow of time</em>".</p>
<p>There was a comment (of mine) that the confusion is not bet... | 4,994 |
<p>I have the following readings for length of a wire:</p>
<p>10.2 ± 0.1 cm</p>
<p>10.3 ± 0.1 cm</p>
<p>10.1 ± 0.1 cm</p>
<p>10.2 ± 0.1 cm</p>
<p>Now, when I find out the mean value, I get:</p>
<p>(10.2 ± 0.1 + 10.3 ± 0.1 + 10.1 ± 0.1 + 10.2 ± 0.1) cm / 4</p>
<p>So, will I get the answer as (10.2 ± 0.1) cm or (1... | 4,995 |
<p>Let's say that you are doing some Monte-Carlo simulations of a statistical system on a lattice and you observe scale invariance, meaning that you are at a conformal point. Can you get a numerical appreciation of the central charge?</p>
<p>I know how the central charge is related on the free energy (on a cylinder fo... | 4,996 |
<p>In an certain question my teacher asked to find the maximum force. She said that the maximum force in electrostatics means $\frac{dF}{dx}=0$. Why is it like that?</p> | 4,997 |
<p>If we place two glass plates of refractive index n and each having thickness t,on the way of a light ray the increase in optical path becomes <img src="http://i.stack.imgur.com/7p0h5.jpg" alt="enter image description here"> (S2P-S1P)=2(n-1)t due to refraction through them,and the path difference(or extra path traver... | 4,998 |
<p>There is known to be a lower limit on space, which can be derived from the Planck units. It can describe the minimum distance resolvable between two points; but what then would the structure of space look like?</p>
<p>Would it be a lattice, where each point of space, planck length apart on each axis, forms the 3 di... | 173 |
<p>Recently I learned about a technique in image processing, which has its roots in something called the 'heat equation' from physics. The original creators of this technique were inspired by the physics of how heat diffuses through an object. </p>
<p>The objective of course is to 'smooth out' the image, for general n... | 4,999 |
<p>I made a simple bulb-battery circuit and then I cut one of the wires and attached both ends to cemented floor, the bulb didn't glow, this means <strong><code>cemented floor</code></strong> is a poor conductor of electricity. Then how does <strong>earthing</strong> work ? This idea of activity came from when I got a ... | 5,000 |
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