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<p><img src="http://i.stack.imgur.com/H8qNp.png" alt="enter image description here"></p>
<p>I saw this graph about the electrons density in different altitudes and difference between night and day, the difference between the 2 electron densities (day and night) decreases till 300 Km (F2 layer) and then the difference... | 1,124 |
<p>I'm not a physicist and I do not understand maths. But I watch documentaries about "how it all began", "the big bang", "What is time", etc etc just really fascinating. </p>
<p>I was wondering if a blackhole would get in contact with another blackhole, which one would consume time and space? Because they have both i... | 1,125 |
<p>So I am a little confused on how to deal with the Kilowatt hours unit of power, I have only ever used Kilowatts and I have to design a residential fuel cell used as a backup generator for one day.</p>
<p>The average power consumption of a US household is 8,900 kW-hr per year and 25 kW-hr per day and approximate 1 k... | 1,126 |
<p>I am using an old BBO crystal, which is not designed for spontaneous parametric down conversion, to see whether I can generate converted photons of 800nm from 400nm. I used a photon avalanche detector and I observed some signal of 800 but I couldn't observe them directly or by a CCD.</p>
<p>I would like to know whi... | 1,127 |
<p>Could a very small black hole where half of its entropy has been radiated, emit Hawking radiation that is macroscopically distinct from being thermal? i.e: not a black body radiator. Or would the scrambling property mean that the initial states that produce the non-thermal Hawking radiation are micro states that are... | 1,128 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/17524/path-to-obtain-the-shortest-traveling-time">Path to obtain the shortest traveling time</a> </p>
</blockquote>
<p>I've been told that if one would want to make a ramp to get a ball from point A to a... | 6 |
<p>I would be very curious if Kerr black holes emit Hawking radiation at the same temperature in the equatorial bulges and in their polar regions. I've been looking some reference for this for a couple of months now but i haven't been successful yet.</p>
<p>According to <a href="http://physics.stackexchange.com/a/4683... | 1,129 |
<p>I was driving uphill from a complete stop for a distance of .4 miles estimated to take 1 minute in a navigation app. I was pulled over right after cresting the hill. The cop had me on radar going 53mph. What do I need to know to see if it was possible to be going that fast uphill ? The grade of the incline? The 0 to... | 1,130 |
<p>I'd like to learn modern physics at an advanced level, but since I've no access to university, I'm self-teaching, and appeal to the Internet for information about what to study and how.</p>
<p>Currently, I'm trying to form a strong mathematical background. Until now, I've studied basic Linear Algebra and Affine/Euc... | 1,131 |
<p>I have a simple question about general relativity and the Einstein field equations, I wonder if you can specify the stress energy tensor, i.e. specify some mass distribution in space and then calculate the curvature to later find equations of motions etc, instead of starting out with how the geomerty would look. I a... | 1,132 |
<p>I came across this problem in physics "Physics for Scientists and Engineers
with Modern Physics by Serway"</p>
<blockquote>
<p><em>A block on the end of a spring is pulled to position $x = A$ and released from rest. In one full cycle of its motion, through what total distance does it travel?</em></p>
</blockquote... | 1,133 |
<p>According to <a href="http://en.wikipedia.org/wiki/Hill_sphere" rel="nofollow">Wikipedia</a>, Hill Sphere is : the volume of space around an object where the gravity of that object dominates over the gravity of a more massive but distant object around which the first object orbits.</p>
<p>True as this may be, it ju... | 1,134 |
<p>If you have a projectile with these variables.
$x_0 = 1v_{0x} = 70, y_0 = 0, v_{0y} = 80, a_x = 0, a_y = -9.8$
I know how to plot these points with this equation.
$$ x = x0 + (v_{0x})t + 1/2((a_x)t^2) $$
$$ y = y0 + (v_{0y})t + 1/2((a_y)t^2) $$</p>
<p>I want to add air resistance to this problem and i know its a sp... | 7 |
<p>Sorry for the strange question, but why is it that many of the most important physical equations don't have ugly numbers (i.e., "arbitrary" irrational factors) to line up both sides? </p>
<p>Why can so many equations be expressed so neatly with small natural numbers while recycling a relatively small set of physica... | 1,135 |
<p>I'm given a parallel plate capacitor with plate separation of 4mm and plate area 20cm^2. I've calculated the capacitance to be 4.425 x 10^-10 F. I'm asked to also find the maximum voltage and charge the capacitor can store.</p>
<p>If I'm using the right equations then the voltage should be V = Ed and the charge sho... | 1,136 |
<p>Can a machine deconstruct objects on an atomic level. But is that possible? Not the machine per say but the simple (not that simple) act of what it does. Ex.Taking a broken computer and separating the different atoms so it would be just a group of atoms instead of a computer. </p>
<p>If you have any suggested rea... | 1,137 |
<p>If I have a 12V 4Ah lead acid battery and use a battery charger that, let's say for example, can charge 10A, 50A, or 100A. If I theoretically turned it to 100A will the battery explode?</p>
<p>I understand that when you use a higher amperage the battery will charge quickly but due to resistance and flow of ions a l... | 1,138 |
<p>When Chiral Symmetry was exact, as it was before EWSB due to the lack of mass terms for quarks, would the residual strong force have infinite range? Related to this, does the Negative Beta Function apply for the Nuclear Force, or does it only affect the Strong Force within nucleons?</p> | 1,139 |
<p>I am searching the literature for the Flory-Huggins phase diagram with the following components : polymer, solvent, and a third component that does not interact with the other components (just entropy effects). It must have been done but I can't find the special case in which the third component is not interacting. ... | 1,140 |
<p>As the Feynman diagram shows above. Does the s-channel and t-channel stands for exactly same reaction or they have big difference?</p>
<p>Many thanks in advance
enter image description here</p>
<p><img src="http://i.stack.imgur.com/VG6GR.png" alt="enter image description here"></p> | 1,141 |
<p>Can elementary particles (like the electron, photon, or neutrino ) go through an atom (not the nucleus)?</p> | 1,142 |
<p>We know that if we take Fourier transform of momentum we go to position space. But why Fourier transform only.(credit_ Abh Gupta)</p> | 8 |
<p>I know that the weather balloon will eventually be stopped because of the atmosphere no longer being buoyant but would the balloon be able to go farther than it regularly would?</p> | 1,143 |
<p>I was doing some static equilibrium problems and I came across this problem which should be easy to solve, but is posing quite a challenge. I want to point out that this is <strong>not</strong> homework, just plain old studying. By the way, I don't know how to format mathematical equations and I think writing them o... | 1,144 |
<p>I recently saw this video on youtube:</p>
<p><a href="http://www.youtube.com/watch?v=oJfBSc6e7QQ" rel="nofollow">http://www.youtube.com/watch?v=oJfBSc6e7QQ</a></p>
<p>and I don't know what to make of it. It seems as if the theory has enough evidence to be correct but where would all the water have appeared from? W... | 1,145 |
<p>Given an action of the form </p>
<p>\begin{equation}S=-\frac{1}{4}\int d^4x\eta^{\mu\nu}\eta^{\lambda\rho}F_{\mu\lambda}F_{\nu\rho}\end{equation}</p>
<p>where $F_{\mu\nu}=\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu}$, $\eta_{\mu\nu}=g_{\mu\nu}/a^2(\eta)$, where $g_{\mu\nu}$ is given by the line element:</p>
<p>\be... | 1,146 |
<p>How do I understand that the action for the free relativistic scalar field theory is non linear? What will be the associated interaction potential of that equation?</p> | 1,147 |
<p>Measurement of a quantum observable (in an appropriate, old-fashioned sense) necessarily involves coupling to a system with a macroscopically large number of degrees of freedom.
Entanglement with this "apparatus" takes care of the decoherence. It is often said (I can provide references upon request) that the remaini... | 1,148 |
<p>I was ruminating the explanations about how boats can sail against the wind (or "<a href="http://www.ksl.com/?sid=19781767" rel="nofollow">into the wind</a>"), and wondered if one could devise a simple mechanical model without hydrodynamics involved. </p>
<p>Imagine a cart (in red in the figure) that is allowed to ... | 1,149 |
<p>We see the crab pulsar, we don't see any compact remnant from Supernova 1987A.
I can't find any others, but I believe they exist. Help?</p> | 1,150 |
<p>Given the numerous chemical compounds found in dry air [compressed into a liquid] of a given volume [lets say $22.4$ L for simplicities sake] whose atomic weights far surpass that of water alone assuming water is $H_2 O$. Why does $22.4$ L of compressed liquid air weigh less than the same bucket of liquid water?</p> | 1,151 |
<p>A rather simple question:
Starting from an electrically neutral state, pairs of top quarks are produced as top and anti-top, and denoted as $t\bar t$. </p>
<p>Now the production of pairs of scalar top quarks, the supersymmetric partners of the top quarks, seems to be commonly denoted as $\tilde t \tilde t^*$ (e.g. ... | 1,152 |
<p>Micro-channel plate (MCP) detectors are used to detect photons, electrons or charged particles. But how can MCPs be used to detect neutral particles? In ion traps, the neutral molecules (after being irradiating with a laser, the ions fragment or lose electrons to produce neutral molecules or fragments) are detected ... | 1,153 |
<p>I came across this question while having conversation with one person.
We know that <a href="http://en.wikipedia.org/wiki/Center_of_mass" rel="nofollow">Center of Gravity</a> of a solid cube is at the intersection of connecting the opposite vertex of the cube.
Suppose, you have a hollow cube, filled with water/air. ... | 1,154 |
<p>The force on a small element (of length dl) of a current carrying wire, place in a magnetic field <strong>B</strong> can be calculated using the following equation (which is simply an application of the Lorentz force equation):</p>
<p>d <strong>F</strong> = i <strong>dl</strong> X <strong>B</strong></p>
<p>My ques... | 1,155 |
<p>What makes the beam of some lasers: </p>
<p>1-visible?
such as the ones used in clubs or such as the laser pointers sold at amazon which if pointed to the sky look like a solid visible beam of light crossing the sky (it reminds me of the laser sword in star wars)</p>
<p>2-invisible?
such as the ones used in poin... | 1,156 |
<p>How to derive an expression for entropy in form of</p>
<p>$S = \ln \Omega$</p>
<p>from the form</p>
<p>$\displaystyle{S = - \sum_i \; p_i \ln p_i}$ ?</p>
<p>That is the last formula taken as a definition of entropy.</p>
<p>Just a reference will do. The backwards derivation (probably with some assumptions) is gi... | 1,157 |
<p>If you bombard an electron shell with a photon below the critical level to promote the electron to a higher state, will the shell absorb nothing and the photon get deflected with the same amount of frequency/energy that it came with initially?</p> | 1,158 |
<p>I am a mathematician, not a physicist, so please be gentle with me if I write something wrong.</p>
<p>Consider a bounded, regular container $\Omega$, which is filled with the fluids $F_1,...,F_N$ which do not mix (i.e. $\bigcup_{i=1}^N F_i=\Omega$ and $F_i\cap F_j=\emptyset, \forall i\neq j$). Between two adjacent ... | 1,159 |
<p>I am very confused that some atoms called high spin or magnetic atoms have spin level more than $\frac{1}{2}$ but are still said to have $SU(2)$ symmetry.</p>
<p>Why not $SU(N)$?</p> | 1,160 |
<p>I require a software to simulate Fluid simulation with the capability of supporting vacuum simulation. My requirements are that all numbers must reflect their real counterparts almost exactly. For example I need to mix Fluid, Air and Vacuum.</p>
<p>I have tried RealFlow but it doesn't support Vacuum. </p>
<p>Any b... | 1,161 |
<p>I was trying to solve frictionless inclined plane problem using a diff. frame as shown in the figure, and can't figure out that acceleration along the plane = g.sin(Θ), but I think it should be = g/sin(Θ) as according to the figure. </p>
<p>I have gone through numerous examples and theory regarding such cases, but ... | 1,162 |
<p>I would like to demonstrate the several forms of the Friedmann equations WITH the $c^2$ factors. Everything is fine ... apart that I have a missing $c^2$ factor somewhere.</p>
<p>In all the following $\rho$ is the <strong>mass density</strong> and not the energy density $\rho_{E}=\rho c^2$</p>
<p>If we look at the... | 1,163 |
<p>Does temperature affect the internal resistance of batteries? And does charging a "frozen" battery allow it to charge faster than a warm or room temperature battery?</p> | 1,164 |
<p>Is there a simple account of why technetium is unstable?</p>
<p>From the <a href="http://en.wikipedia.org/wiki/Technetium#Isotopes">Isotopes section</a> of <a href="http://en.wikipedia.org/wiki/Technetium">Wikipedia's article on Technetium</a>:</p>
<blockquote>
<p>Technetium, with atomic number (denoted Z) 43, i... | 1,165 |
<p>Photon is a spin-1 particle. Were it massive, its spin projected along some direction would be either 1, -1, or 0. But photons can only be in an eigenstate of $S_z$ with eigenvalue $\pm 1$ (z as the momentum direction). I know this results from the transverse nature of EM waves, but how to derive this from the inter... | 836 |
<p>If we have the wave function $\psi_{100}(r,\theta,\phi)=R_{10}(r)Y_{00}(\theta,\phi)$ when we are normalising it we do the following:
$$1=\int| \psi_{100}(r,\theta,\phi)|^2sin(\theta) r^2drd\theta d\phi$$ but can we also normalise the individual parts separately i.e.
$$1=\int r^2|R_{10}(r)|^2 dr $$ and $$1=\int |Y... | 1,166 |
<p>I've learned in school that the force in a coil is $F=kx$, linear on how much the coil is stretched. Two questions:</p>
<ol>
<li><p>Is it always linear for every shape of a coil? Does it remain linear if we increase the radius of the coil, increase the length between loops and so on?</p></li>
<li><p>Can we deduce t... | 1,167 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/5456/the-speed-of-gravity">The speed of gravity</a> </p>
</blockquote>
<p>It takes a long time for a radio signal to travel to the planet Mars.</p>
<p>What if we made a special type of radio that could ... | 4 |
<p>In a gravitational field, should the mass distributions always behave well?</p> | 1,168 |
<p>I have tried to learn it myself but I was unable to understand. Can you please explain it in detaails with simple example.</p>
<p>Thanks</p> | 1,169 |
<p>Assume that there are only well behaved functions as mass distributions, and there are no other forces except gravitation. Is it than possible to create an arrangement where a variation of a certain quantity (could be mass density or gravitational field or momentum) has a resonance?</p> | 1,170 |
<p>Is there a computer game using principles of quantum optics or quantum information?</p>
<p>By game I don't mean just a simulation or an interactive course, but something that can be played in an enjoyable way.</p>
<p>By 'principles' I mean actual rules, not just things bearing the same name or vaguely related.</p>... | 1,171 |
<p>What prevents the unobservable universe from being a continuously enlarging sphere due to the inflating bubble universes? Our observable universe being close to flat could support such a scenario?</p> | 1,172 |
<p>Which conformal QFTs do we know for spacetime dimension d > 2?</p>
<p>I know that for D = 4 we have N = 4 SYM and some N = 2 supersymmetric Yang-Mills + matter models.</p>
<blockquote>
<p>What is the complete list of such QFTs? Is it plausible we know all of them? In particular, what examples do we have with D =... | 1,173 |
<p>I have been wondering about some of the different uses of Generalized Complex Geometry (GCG) in Physics. Without going into mathematical detail (see <a href="http://arxiv.org/abs/math/0401221">Gualtieri's thesis</a> for reference), a Generalized Complex Geometry attempts to unify symplectic and complex geometry by c... | 1,174 |
<p>Extended TQFT and CFT have been puzzling me for while. While I understand the mathematical motivation behind them, I don't quite understand the physical meaning. In particular, it's not clear to me to which extent these constructions produce more information (i.e. allow for several "extended" versions of the same "n... | 1,175 |
<p>Lets say i have $n$ different objects that effects each other only by the classic gravity force.</p>
<p>I have their initial locations, masses and velocity's:</p>
<p>$$ x_1(0),\cdots,x_n(0) $$
$$ m_1,\cdots,m_n $$
$$ v_1(0),\cdots,v_n(0) $$ </p>
<p>Is it possible to describe each object location with an equation... | 1,176 |
<p>A paradox (Ex.: if someone goes back in time to kill their own grandfather, then they won't exist, but then they wouldn't be able to go in time to kill their grandfather, but then they WOULD exist, but then they would go back in time...) is, really, the only "perpetual motion machine" (and I know I use that term loo... | 1,177 |
<p>Short version:</p>
<p>Is it a physical problem (crystal structure/grains/redox/etc.) or just a logistics problem (keeping the solutes from homogenizing, molten/solid/temperature related problems) that keeps us from commonly employing objects that have transitioning alloy compositions throughout the object? </p>
<p... | 1,178 |
<p>I want to know that if you are given a very complex equation g(x)=A(T). How could you solve for x, which is a function of variable T. To be more specific, I encounter a polylogarithmic function I need to solve numerically..</p> | 1,179 |
<p>In Bose-Hubbard model, we neglect the hopping term in atomic limit (U>>t) and the dominant interaction term result in a Mott Insulator phase. In hard core boson limit ($U \rightarrow \infty$), there is no double or higher occupancy are suppressed (n=0 or 1), so the interaction term in the Hamiltonian vanishes and th... | 1,180 |
<p>Here is an extremely naive question: Why would the apple fall under the tree?</p>
<p>I am puzzled by this, because the conventional answer that the gravity between the apple and the earth pulling apple down is not satisfactory to me. My thought process goes as follows:</p>
<ol>
<li><p>We know that in an appropriat... | 1,181 |
<p>I am a beginner to study QFT and have a problem.</p>
<p>I know, in Dirac equation, thanking to the Pauli exclusion principle and believing that the vacuume is the state that all the negative energy states are occupied and all the positive energy states are empty, the antiparticles in Dirac equation are not occupied... | 1,182 |
<p>I'm watching Susskind's video lectures and he says in the first lecture on classical mechanics that for a physical law to be allowable in classical mechanics it must be reversible, in the sense that for any given state $S\in \mathcal{M}$ where $\mathcal{M}$ is the configuration space there should be only <em>one</em... | 1,183 |
<p>So I have seen an animation about Stephen Hawking (after his recent study state universes claim) that Hawking evaporation is due to negative mass; But how is this possible? I mean, there is no such thing as negative mass!</p> | 1,184 |
<p>In the paper <a href="http://arxiv.org/pdf/hep-th/9804191.pdf" rel="nofollow">here</a>(page 7-8) the authors make a claim that the Natanzon potential (an implicit potential) follows an $SO(2,2)$ algebra. This potential defined as :</p>
<p>$$ U(z(r)) = \frac{h_1z(r)+h_0(1-z(r))-fz(r)(1-z(r))}{R(z)} - \frac{1}{2}\le... | 1,185 |
<p>The Spread Networks corporation recently laid down 825 miles of fiberoptic cable between New York and Chicago, stretching across Pennsylvania, for the sole purpose of reducing the latency of microsecond trades to less than 13.33 milliseconds (http://www.spreadnetworks.com/spread-networks/spread-solutions/dark-fiber-... | 1,186 |
<p><a href="http://en.wikipedia.org/wiki/Density_functional_theory" rel="nofollow">Density Functional Theory</a> (DFT) is usually considered an electronic structure method, however a paper by <a href="http://arxiv.org/abs/physics/9806013" rel="nofollow">Argaman and Makov</a> highlights the applicability of the DFT form... | 1,187 |
<p>Does constructing huge buildings affect the rotation of the Earth, similar to skater whose angular rotation increases when her arms are closed comparatively than open?</p> | 1,188 |
<p>Since I don't know how to add another question to an already existing topic,
I'm opening a new thread. However I'm referring to:
<a href="http://physics.stackexchange.com/questions/8201/beginners-questions-concerning-conformal-field-theory">Beginners questions concerning Conformal Field Theory</a> </p>
<p>As noted... | 1,189 |
<p>As compared to when the coffee is just hot from brewing. I suspect it has something to do with the way the microwaves are affecting the molecules of the coffee.</p> | 1,190 |
<p><img src="http://i.stack.imgur.com/KYj8v.png" alt="enter image description here"></p>
<p>Having trouble with a FBD moment. The problem is:</p>
<blockquote>
<p><em>How big can the force couple C (looks like a G in the pic) be in order for the disk to not spin? The disc has mass m and the beam also has mass m. All... | 1,191 |
<p>Why does a <a href="http://en.wikipedia.org/wiki/Wave_function_collapse" rel="nofollow">wavefunction collapse</a> when observation takes place?
Can this question be explained in non mathematical terms? I have tried finding the answer but couldn't find a clear explanation.</p> | 1,192 |
<p>I am unable to derive the Hamiltonian for the electromagnetic field, starting out with the Lagrangian
$$
\mathcal{L}=-\frac{1}{4}F^{\mu\nu}F_{\mu\nu}-\frac{1}{2}\partial_\nu A^\nu \partial_\mu A^\mu
$$
I found:
$$
\pi^\mu=F^{\mu 0}-g^{\mu 0}\partial_\nu A^\nu
$$
Now
$$
\mathcal{H}=\pi^\mu\partial_0 A_\mu-\mathcal{L}... | 1,193 |
<p>I'm having some trouble following pages 55-56 of Sakurai's <em>Modern Quantum Mechanics</em>. </p>
<p>We're trying to transfer from position space into momentum space. Here's a quote:</p>
<blockquote>
<p>Let us now establish the connection between the $x$-representation and the $p$-representation. We recall that... | 1,194 |
<p>Is there a way to lower the total spin of the state and fixing the $S_z$ rather than lowering the $S_z$ by spin ladder operator? Or in other words, how to connect the $S=1$ state with $S=2$ or $S=0$ state? Is there such an operation though it might be unphysical?</p> | 1,195 |
<p>When you're in a train and it slows down, you experience the push forward from the deceleration which is no surprise since the force one experiences results from good old $F=m a$. However, the moment the train stops one is apparently pulled backwards. But is that a real physical effect or just the result from leanin... | 1,196 |
<p>The equivalence principle, being the main postulate upon which the general relativity theory rests, basically states that all reference systems are equivalent, because pseudo forces can (locally) be interpreted as gravitational fields and it is therefore impossible for the local experimenter to decide whether he is ... | 1,197 |
<p>I am trying to clarify the relation between random walk and diffusion, and the source book proposes the following which I can't get. Starting from the diffusion equation</p>
<p>$$ \frac{\partial C}{\partial t} = D \frac{\partial^2 C}{\partial x^2}, $$</p>
<p>how can this be solved to get</p>
<p>$$ C = \frac{A}{\s... | 1,198 |
<p>I am trying to figure out what do I need to know to properly simulate the creation of a solar system from a particle cloud with random distribution of hydrogen atoms.</p>
<p>Being more of a programming background than a physicist one, I find some difficulties trying to find all the forces in interaction.</p>
<p>As... | 1,199 |
<p>I am looking to model the nodal surfaces in a resonating closed sphere. The sound source is external. What sort of wave equation will reveal the spherical harmonics depending on the frequency, speed of sound, sphere diameter, possibly other relevant factors?</p>
<p>The purpose is to make a computer simulation befor... | 1,200 |
<p>I heard that the Lagrangian is defined in the path integral formulation of quantum mechanics. How would the Lagrangian in this formulation be used to recover the Schrodinger equation that we normally use?</p> | 1,201 |
<p>Do electrons (individually) have definite and single value of momentum and position or do they simultaneously have multiple position (a spread) at a time?
In other words, according to the uncertainty principle, is it just impossible to <em>measure</em> the exact position and momentum or is it actually impossible for... | 1,202 |
<p>If we know that the Polarization P in LIH dielectrics is proportional to the net field inside the dielectric according to:</p>
<p>P = ε0χeE.....(1)</p>
<p>And we know that</p>
<p>D = εE........(2)</p>
<p>Does it not follow that we can ascertain the polarization directly from the applied (free charge) field, sinc... | 1,203 |
<p>Can the <a href="http://en.wikipedia.org/wiki/Ricci_curvature" rel="nofollow">Ricci curvature tensor</a> be obtained by a 'double contraction' of the Riemann curvature tensor? For example</p>
<p>$R_{\mu\nu}=g^{\sigma\rho}R_{\sigma\mu\rho\nu}$.</p> | 1,204 |
<p>In gravitational lensing, there are three categories of lensing: strong, weak, and micro. As I understand it, strong lensing (just as the name implies) occurs when a source and a gravitational lens are relatively close by and the lens is strong, producing extreme distortions of the light from the source in phenomen... | 1,205 |
<p>Thermodynamic Entropy Variation is defined as
$$\Delta S = \int_i^f \frac{dQ}{T},$$</p>
<p>where $i$ and $f$ are the initial and final states of the process. </p>
<p>My question is: <strong>does this equation apply to quasi-static irreversible processes, or only to reversible processes?</strong></p>
<p>Obviously... | 1,206 |
<p>So, I'm traveling to another star 100 light years away in my spaceship. This ship has a solar sail pushed by a laser beamed from my home star system, so can achieve a velocity close to c. It's also got a robust parachute to slow down with.</p>
<p>I understand that if I measure light coming from my origin star, it w... | 9 |
<p>In the classic Young double slit experiment, with slits labeled as "A" and "B" and the detector screen "C", we put a detector with 100% accuracy (no particle can pass through the slit without the detector noticing) on slit B, leaving slit A unchecked. What kind of pattern should we expect on the detector C? Probably... | 1,207 |
<blockquote>
<p>A box is thrown up an incline with degree $\alpha$. the kinetic-friction coefficient is $\mu_k$. the body returns back to its start point. </p>
<p>a. prove $\frac{t_{down}^2}{t_{up}^2}=\frac{a_{up}}{a_{down}}$.</p>
<p>b. suppose time of getting up the incline is half of the time needed for g... | 1,208 |
<p>an experiment to disprove the statement--"frictional force is irrespective of the surface area in contact."
take a x rs note. fold it in a half and put it in the pocket of a shirt. then invert the shirt. lets assume it doesn't fall. now, take it out, fold it again and repeat the experiment. after a certain no. of f... | 1,209 |
<p>According to Hubble observatory, the age of universe is 14 billion years. But, the distant galaxies are about 40 billion light years. How could that simply be possible? That means the information that we are receiving from those galaxies took place 40 billion yrs ago ?</p> | 10 |
<p>Suppose that we have a Lagrangian density like $$\mathcal L = -\frac{1}{4} \operatorname{tr} F_{\mu\nu}F^{\mu\nu} + \frac{\theta}{32\pi^2} \operatorname{tr} \big( \epsilon^{\mu\nu\rho\sigma} F_{\mu\nu}F_{\rho\sigma}\big) + \overline{\psi}\gamma^\mu D_\mu \psi$$
where $F_{\mu\nu}$ is the gauge field strength and $D_\... | 1,210 |
<p>Let $n_F(\omega) = \large \frac{1}{e^{\beta (\omega)} + 1}$ be the Fermi function.</p>
<p>A fermionic reservoir correlation function is given by:</p>
<p>$$C_{12}(t) = \int_{-\infty}^{+\infty} d\omega~ \tag{5}J_R(\omega) \, n_F(\omega) \, e^{-i\omega t}$$</p>
<p>The Fermi function here is given in terms of Chebys... | 1,211 |
<p>I wondered whether the Fermi-Dirac Statistics describes the anti-fermion particles. Does it include the anti-particles?</p> | 1,212 |
<h2>Dilemma</h2>
<p>The uncertainty principle of energy and the 2nd law of thermodynamics don't add up : the uncertainty principle of energy says that </p>
<p>$\Delta \tau \cdot \Delta E \ge \frac{h}{4\pi} = \frac{\hbar}{2}$ </p>
<p>where $\Delta$ is the uncertainty in measurement.</p>
<p>Now lets consider a situat... | 1,213 |
<p>My son is very keen on Astronomy but I don't know when there are meteor showers or something else that would be worth going out to the country to see. Last year we went to see a meteor shower, but I only knew about it because I'd heard it on the radio.</p>
<p>Which websites list events that we can either see with t... | 1,214 |
<p>it is widely known that elliptical galaxies have little or no gas, but how is this determined? What is the amount of gas? Is there a decent ratio of stellar mass to gas for ellipticals? How does this vary between normal ellipticals and those that were formed by mergers (or still look like merger remnants)? Thank... | 1,215 |
<p>We have : $E=h/f$ </p>
<p>I realised that the problem what quanta solved was that $h/0$ equals infinity but energy can't be infinity. But when frequency is zero we haven't any energy to calculate - there is no real solution. But Planck came with another solution: The light is packages with different energy - so we ... | 1,216 |
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