question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>What's the proof of the light polarization that it happens to the electric field and not the magnetic field? How did Malus discover that the light is polarized although he didn't see the waves polarizing!</p> | g440 | [
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<p>If the magnetic field doesn't polarize does it follow the electric field path of propagation? or does it vanish?</p> | g440 | [
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<p>Why is the strength of a field (i.e. gravitational or electric) inversely correlated to the square of the radius?</p>
<p>It is clear to me why the further you get a way from a field, the field's enacted force decreases. However, this makes me hypothesize that the relationship should be:</p>
<p>$$F ~=~ k/r$$ </p>
... | g441 | [
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<p>This probably sounds really naive. But, a strange discussion came up on Quora about computers possibly weighing more when information is added to them. </p>
<p>I tried looking around but couldn't find a definitive answer. There are a few threads where people have tried to ask something similar.</p>
<p>1) <a href="... | g442 | [
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<p>I read it on Yahoo Answers (link below) that the power of lens changes when the lens is placed inside water. But then, if we consider the formula f=c/2 , the radius if curvature of the lens still remains same, then, how can the focal length change? </p>
<p>While considering the definition (point where light rays me... | g14164 | [
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<p>A <a href="http://www.google.com/search?q=sun+jar" rel="nofollow">sun jar</a> is an object that stores solar energy in a battery and then releases it during dark hours through a led.</p>
<p>Assume:</p>
<ul>
<li>a $65cm^2$ solar panel </li>
<li>a 12h/12h light/dark cycle</li>
<li>insolation of $2.61kWh/m^2/day$</li... | g14165 | [
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<p>What would be a good book or books for a sufficient prerequisite for Zee's book QFT in a nutshell?
I have had a course in QM and relativistic QM, but I think there are some gaps that needs to be filled. </p>
<p>Maybe someone who have read the book can tell me what other books they read or?</p> | g443 | [
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<p>I have a h/w question regarding the current in the armature of a motor when it is operating at half it's normal speed. The question is;</p>
<blockquote>
<p>A motor is designed to operate at 118V and draws a current of 12A when it first starts up. At it's normal operating speed, the motor draws a current of 2A. Co... | g14166 | [
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<p>As a physics newbie I'm trying to get a grip on basic orbital mechanics. I think I'm beginning to get grasp on how bodies interact with each other. When a body approaches another body it accelerates due to gravity. It can reach a point where its velocity is high enough to keep falling but also keep missing the objec... | g14167 | [
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<p>Neutinos are either Dirac particles or Majorana particles but can’t be both at the same time. Then how can we write a general mass term as the sum of a Dirac mass term and a Majorana mass term? When we write such a term what nature of neutrinos (Dirac or Mjorana) do we have in mind? </p>
<p>A massive Dirac field, h... | g14168 | [
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<p>In math, I was taught to parameterize a scalar/vector <a href="http://en.wikipedia.org/wiki/Line_integral" rel="nofollow">line integral</a>. In physics, I remember doing problems where I didn't parameterize the problem and it still came out correct. </p>
<p>So, by parameterization, you'll always get the right answe... | g14169 | [
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<p><img src="http://i.stack.imgur.com/qEWny.jpg" alt="enter image description here"></p>
<p>The answer is same... That us the graph between P and I will also be a parabola.... Similar to the graph between V and I. But how? Can anyone explain through mathematical approach ?
I used $P=V^2/R$ , $P=i^2R$ or $P=VI$ . I di... | g14170 | [
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<p>I read Griffiths EM today and it says something very interesting but a little bothering to me. It states for an atom, the position of center of mass of an electron cloud lies in the center of the proton.</p>
<p>But my question is why? What will happen if this is not true?</p> | g14171 | [
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<p>I am reading Srednicki's book on QFT and there's a thing I don't quite see in chapter 6 (Path integrals in QM)</p>
<p>equation (6.7) is</p>
<p>$\langle{}q^{''},t^{''}|q^{'},t^{'}\rangle=\int\prod_{k=1}^Ndq_k\prod_{j=0}^N\frac{dp_j}{2\pi}e^{ip_j(q_{j+1}-q_j)}e^{-iH(p_j,\bar{q_j})\delta t}$</p>
<p>where he says $\b... | g14172 | [
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<p>I have seen the equation $V = \frac {V_0}{K}$, but also the equation $V=\frac{1}{2}CV^2$. The values of C and V increase in the same linear ration with K (because $C=KC_0$). However, as the energy is proportional to $C$ and $V^2$, the energy stored by the capacitor actually DECREASES with the employment of a diele... | g14173 | [
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<p>What is the difference between rotational velocity & rotational frequency? Their units seem to be the same, and I've read that one is a 'scalar' and the other is a 'vector,' but how do they differ?</p> | g14174 | [
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<p>In case of any miscommunication let me describe my understanding of the meaning of "perturbative" and "<a href="http://en.wikipedia.org/wiki/Non-perturbative">non-perturbative</a>", and correct me if something is wrong:
In a perturbatively defined QFT the fields are quantized as free fields, and the interaction is c... | g14175 | [
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<p>Give an example of a situation in which there is a non-zero gravitational field and a zero gravitational potential at the same point?</p>
<p>$$dV=-\vec E\cdot d\vec r.$$</p>
<p>The above equation implies that such a situation is possible.</p> | g14176 | [
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<p>I have some questions about the statistics of Bell Tests. For convenience I'm going to refer to the test described in this paper:</p>
<p><a href="http://arxiv.org/abs/quant-ph/0205171" rel="nofollow">http://arxiv.org/abs/quant-ph/0205171</a></p>
<p>They show a coincidence rate of 300 counts with polarizers aligned... | g14177 | [
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<p>In <a href="https://www.youtube.com/watch?v=IybCTI4aC5s" rel="nofollow">this video</a> we see a rather unorthodox bowling technique on display. The gentleman appears to knock over all of the pins using only a ping pong ball. It's a fake, of course: you could never knock over a bowling pin with a ping pong ball. Or c... | g14178 | [
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<p>So according to my notes, the field inside a conductor is zero. But what, exactly, is meant by inside?</p>
<p>I think we are in electrostatics for the purpose of this question.</p>
<p>The reason it is zero is because all the electrons are pushed to the edge of the conductor. So are these electrons assumed to be no... | g14179 | [
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<p>A recent <a href="http://arxiv.org/abs/1204.3924" rel="nofollow">arXiv</a> article measures the variation of gravitational potential in a local region around the solar system, and from that it tries to infer the mass density. Are there any valid counterarguments to their conclusion, i.e: that there is no dark matter... | g14180 | [
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<p>if gravity travels at c(light speed), why aren't objects pulled to earth at that speed? </p>
<p>Since the velocity of gravity is 9.8 meters per second squared, will it eventually accelerate until it maxes out at c then hold constant? </p>
<p>And if that is the case, then why doesn't the gravitational pull between ... | g14181 | [
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<p>I'm reading Einstein Gravity in a Nutshell (by Zee) and here he defines a vector as an object which is invariant under coordinate representation; concretely, if in one coordinate representation, $V$, $p_V=(p^1,p^2)$ then when we transform it via a rotation $p_W = R(\theta)p_V$ then we do not violate any physical la... | g14182 | [
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<p>Suppose there is an isolated system $A$ at time $(-\infty, t_1)$, whose entropy is $S=S_{max}$, i.e. it is at thermodynamical equilibrium.</p>
<p>Between moments $[t_1, t_2)$ the isolation is violated and system's entropy is decrased $S = S_{max} - S_d, \space\space\space 0<S_d <S_{max}$.</p>
<p>Question: th... | g14183 | [
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<p>Where does an object "obtain" kinetic energy? I understand that an object often gets kinetic energy from another object. Where does the first object get the energy?</p> | g14184 | [
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<p><img src="http://i.stack.imgur.com/T1TPW.gif" alt="Free Body Diagram">
Hello,</p>
<p>I'm working on a small hardware project.</p>
<p>I have two load sensors located at distance $S_1$ ($x=0$) and $S_2$. Assuming we ignore the weight of the ramp ...</p>
<ul>
<li>What is the load on $S_1$ and $S_2$ as a function of ... | g14185 | [
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<p>A creationist website makes this argument for the 6,000 year old earth. I'm embarrassed to say I don't know how to do the math to evaluate the claim myself. However, the time scales involved seems to lend some credence to this argument. "The Moon is slowly drifting away from the Earth. If it is getting further, a... | g14186 | [
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<p>I've heard that clear things such as the gaseous components of the atmosphere or water reflect no light, and that is why they are clear. I've also heard that black things such as asphalt are such because they reflect no light. What is the physical reason for these things to reflect no light yet be totally opposite, ... | g14187 | [
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<p>I am trying to understand how this linear motor works:</p>
<p><img src="http://i.stack.imgur.com/ymWB4.jpg" alt="enter image description here"></p>
<p>You can see a video <a href="http://www.youtube.com/watch?v=UX-_xt2m-pk%20%22%22" rel="nofollow">here</a> for more details. From what I know each permanent magnet c... | g14188 | [
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<p>Hypothetically, I have a circuit with a two $10\Omega$ resistors in parallel. I supply them say, $2V$. How do I calculate the current?</p>
<p>What if, say, the circuit now has a $10\Omega$ resistor and a $5\Omega$ resistor in parallel with $2V$. Will anything change? I'm looking for calculations here.</p> | g14189 | [
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-0.07339542359113693,
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0.03401742... |
<p>Is the fine tuning that cosmologists talk about (that our Universe is fine tuned for intelligent life) is the same as the fine tuning of the squared mass parameter of the Higgs in the Standard Model? And that in SUSY models?</p>
<p>Also, could anyone refer me to a source that explains the fine tuning issue in gener... | g14190 | [
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<p>This is perhaps a simple tensor calculus problem -- but I just can't see why...</p>
<p>I have notes (in GR) that contains a proof of the statement </p>
<blockquote>
<p><em>In space of constant sectional curvature, $K$ is independent of position.</em></p>
</blockquote>
<p>Here </p>
<blockquote>
<p><em>$$R_{ab... | g14191 | [
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0.02805074118077755,
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-0.01936... |
<p>The pressure for the ultrarelativistic Bose gas is </p>
<p>$$p~=~U/(3V) ~\propto~ (kT)^4/(hc)^3.$$ </p>
<p>It looks to me like it diverges for $h \to 0$. Looking at the derivation, it diverges because $h$ is the unit volume in phase-space and letting it go to zero allows for an infinite number of states per volume... | g14192 | [
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<p>Why do the four spin 3/2 $\Delta$ baryons have nearly identical masses and lifetimes despite their very different $u$ and $d$ quark compositions?</p> | g14193 | [
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<blockquote>
<p>What is an example for a system, which is in <a href="http://en.wikipedia.org/wiki/Chemical_equilibrium" rel="nofollow">chemical equilibrium</a>, but not in <a href="http://en.wikipedia.org/wiki/Thermodynamic_equilibrium" rel="nofollow">thermodynamical equilibrium</a>? </p>
</blockquote>
<p>And what ... | g14194 | [
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<p>In many popsci articles it is claimed that String Theory (ST) birthed SUSY. Yet ST was originally invented as a bosons-only theory, that later on brought fermions into the fold. This was only possible After SUSY was incorporated. Hence the old moniker, Superstrings.
My understanding is that string theory (ST) is a ... | g14195 | [
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<p>The force $F$ to carry a plate of area $A$ with velocity $v$ in a fluid of depth $d$ <a href="http://en.wikipedia.org/wiki/Viscosity" rel="nofollow">is given by</a></p>
<p>$$\frac{F}{A}=\eta\frac{v}{d}.$$</p>
<p>Hence if the depth is $kd$, the force becomes $F/k$. </p>
<blockquote>
<p>Do this relations hold for... | g14196 | [
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<p>For my level of understanding the only explanation of mass to energy, ie nuclear weaponry, is limited to a simple summing game where a mass deficit is expressed as energy. For the 'reverse' process, ie in the LHC at CERN, it is a similar story, energy in, mass out. </p>
<p>Is there a more detailed physical explana... | g14197 | [
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<p>I have heard many times that we can treat a moving particle as a: </p>
<ol>
<li><p>classical particle</p></li>
<li><p>non-relativistic</p></li>
<li><p>relativistic particle</p></li>
<li><p><strong>ultra-relativistic</strong> particle</p></li>
</ol>
<p>While I know equations for 1, 2, & 3, I really don't know w... | g14198 | [
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<p>I was wondering what the electric field of a uniformly charged <a href="http://en.wikipedia.org/wiki/Spherical_cap" rel="nofollow">spherical cap</a> is? Thereby I am referring to a spherical shell that was sliced into two pieces and we are only looking at one part of it. So in spherical coordinates it would mean tha... | g14199 | [
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<p>Sorry about my poorly worded question as i'm not to good at explaining but bare with me so here i go.</p>
<p>Does sound come as straight lines like ||||| and become diffracted into curves when it passes through a slit so it looks like )))))?</p>
<p>If this is the case (as most diagrams on the net show), my questio... | g14200 | [
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<p>I'm looking for the exact correspondence between
Lorentz transfer four vector </p>
<p><img src="http://i.stack.imgur.com/5Ws5L.png" alt="Lorentz transfer four vector"></p>
<p>and the four vector of scalar and vector potential $A^\mu = (\phi(t,\vec{x}),\vec{A}(t,\vec{x}))^{T}$.</p>
<p>Does $ct=A(t), x=\phi(t),y=\p... | g14201 | [
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<p>I am very confused about orbital velocity for satellite launched from earth. It is states that:
$$
v=\sqrt{\frac{GM}{r}}
$$
Some says that it is equal to 8000 m/s and some say 3.1 km/s. Please remove my doubt. </p> | g14202 | [
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<p>If we write something like: </p>
<p>$\partial_a X_{\mu} \partial^a X^{\mu}$</p>
<p>Does that mean the first derivative is only applied to the first X? </p>
<p>($\partial_a X_{\mu})( \partial^a X^{\mu}$)</p>
<p>Or is the first derivative applied to the object $X_{\mu} \partial^a X^{\mu}$, such that second derivat... | g14203 | [
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<p>when a body is subjected to $0 K$ temperature, it becomes rigid. hence if we see in terms of quantum the lattice vibration decreases, resulting in no change in the direction of the Random velocity, then can we increase the degree of probability of finding of an electron in an given sys</p> | g14204 | [
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<p>The glasses that we use for 3D viewing does it allow infrared rays to pass through them. Infrared rays pass through normal glass right? I need the pupil illuminated through infrared LEDs so I need to know does the infrared rays pass through each and every kind of glass.</p> | g14205 | [
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<p>My intuitive understanding is that although atoms are mostly empty space, the nucleus is solid. Thus a neutron or a neutrino can collide with it and do things like deflect or cause a nuclear reaction. </p>
<p>But does this intuition reflect the underlying reality? Since we usually think of a solid in reference t... | g14206 | [
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<p>I am trying to start from:
\begin{align*}
[\phi(x),\pi(x')] = i\hbar\delta(x-x') \\
[\phi(x),\phi(x')] = [\pi(x),\pi(x')]=0
\end{align*}
to derive:
\begin{align*}
[a(k),a(k')^\dagger]=\delta_{kk'}\\
[a(k),a(k')]=[a(k)^\dagger,a(k')^\dagger]=0
\end{align*}</p>
<p>So starting with:
\begin{align*}
\phi(x) = \sum_k \le... | g14207 | [
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... |
<p>I took quantum mechanics from our school's electrical engineering department. It was a grad level class designed for students working in device physics, thus it covered a lot of materials: from the basics (Schrodinger's equation, tunneling, the harmonic oscillator), to statistical physics (variational methods, Fermi... | g14208 | [
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<p>There is no atmosphere for comets to get hot and burn and show tails but they still have tails. Why do they?</p>
<p>Edit: Isn't the answer "acceleration"?</p>
<p><img src="http://i.stack.imgur.com/bdR0F.gif" alt="enter image description here"></p> | g14209 | [
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<p>We are told to wear light clothes in summer as they are better at reflecting sunshine and keeping us cool. And dark clothes absorb sunshine and keep us warm.</p>
<p>But is it really relavent? If I buy identical t-shirts, one in black and one in white, will I feel significantly cooler or warmer? I have noticed that ... | g14210 | [
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<p>According to <a href="http://www.guardian.co.uk/science/blog/2012/jul/04/higgs-boson-discovered-live-coverage-cern" rel="nofollow">http://www.guardian.co.uk/science/blog/2012/jul/04/higgs-boson-discovered-live-coverage-cern</a>, the reporter says that higgs boson things are little over <a href="http://en.wikipedia.o... | g14211 | [
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-0.... |
<p>Will this unite some theories, or cause some other change in physics, and perhaps our undertanding of the universe?</p> | g14212 | [
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<p>We already had definition of mass based on gravitational interactions since before Higgs. It's similar to charge which is defined based on electromagnetic interactions of particles.</p>
<p>Why did Higgs need to introduce concept of universe-wide Higgs field to define mass, based on interactions with it? And nobody ... | g217 | [
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<p>The relationship between the steady state theory and the notion of Higgs boson is not clear to me. What does the discovery of Higgs boson mean for steady state theory? Or are the two ideas purely orthogonal?</p> | g14213 | [
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<p>I have a question that I am just curious about.</p>
<p>Two principles: </p>
<p>Magnetic fields and Magnetic susceptibility </p>
<p><a href="http://en.wikipedia.org/wiki/Supercavitation" rel="nofollow">Supercavitation</a> is the use of cavitation effects to create a bubble of gas inside a liquid large enough to en... | g14214 | [
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<p>Through unit analysis, one can identify the following relationship linking energy, action and power:
$energy^2 = action \times power$</p>
<p>Alternatively, we rewrite this expression as:</p>
<p>$power = \frac{energy^2}{action}$</p>
<p>or;</p>
<p>$action = \frac{energy^2}{power}$</p>
<p>In light of this tight re... | g14215 | [
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<p>What "breakthrough" from a theoretical point of view is needed for solar energy to become feasible energy alternative?</p> | g14216 | [
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<p>In late 2003, Edward Witten released a <a href="http://arxiv.org/abs/hep-th/0312171">paper</a> that revived the interest in Roger Penrose's twistors among particle physicists. The scattering amplitudes of gluons in $N=4$ gauge theory in four dimensions were expressed in a simple way using the twistor variables. Witt... | g14217 | [
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<p>So I'm pretty sure I'm approaching this problem in the wrong way and I need some guidance (my first hint is that I think I'm thinking about a quantum mechanical problem too classically)</p>
<p>Suppose there is an isolated molecule in the gas phase with an average cross-sectional area to be exposed to radiation of $... | g14218 | [
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0.009367446415126324,
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<p>I did not understand if a current I above a conducting surface why we take image of current to find magnetic field intensity why not take the effect of actual current only . And is this method and equations to satisfy boundary condition at the surface </p>
<p>Also is there any good tutorial that explain methods of ... | g14219 | [
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<p>Is there anything known about the spatial configuration of the quarks within a proton of pion? Or are they just considered to be two or three overlapping points?</p> | g14220 | [
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<p>I have been (independently) working on Problem 2.13 in Kleppner and Kolenkow's <em>An Introduction to Mechanics</em> and come to an answer which conflicts with the hint the authors provided in the book. The problem is this:</p>
<blockquote>
<p>A "pedagogical machine" is illustrated in the sketch. All surfaces ar... | g14221 | [
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0.0... |
<p>If i have 2 coordinate systems (CS) which are travelling one towards another. CS $xy$ with an observer in its origin and CS $x'y'$ with a source in its origin. Correct me if I am wrong, but i think that I have to use this variation of an equation for a <a href="http://en.wikipedia.org/wiki/Relativistic_Doppler_effe... | g14222 | [
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<p>From everything I've read about quantum mechanics and quantum entanglement phenomena it's unobvious for me, why quantum entanglement is considered to be active link. I.e. it's stated every time that measurement of one particle <em>affects</em> another.</p>
<p>While in my head there is less magic explanation: the en... | g61 | [
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0.02... |
<p>Some of you may know this experience (<a href="http://www.youtube.com/watch?v=0i2lhO3bSjQ">Grape + Microwave oven = Plasma video link</a>):</p>
<ul>
<li>take a grape that you almost split in two parts, letting just a tiny piece of skin making a link between each half-part.</li>
<li>put that in a microwave oven, and... | g14223 | [
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0.005545352585613728,
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<p>Take a displacement in three dimensions and reduce the number of dimensions by one. The original displacement loses one degree of freedom; giving it two parameters to specify a magnitude and an orientation. Now reduce the number of dimensions to just one, leaving just a magnitude... or does it?</p>
<p>For a displac... | g14224 | [
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<p>What math do I want to focus on for 1) quantum computing and 2) quantum physics?</p>
<p>I am interested in studying quantum computing and the Higgs Boson (quantum physics?) and ultimately working in some capacity at the CERN in Europe. I am learning by myself and making progress, self-tested have succeeded in Calc... | g14225 | [
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0.06249917298555374,
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<p>I'm trying to find Susskind and Glogower's original paper,</p>
<blockquote>
<p>L. Susskind and J. Glogower, <em>Quantum mechanical phase and time operator,</em> Physics 1 (1964) 49-61,</p>
</blockquote>
<p>where they propose their exponential and sine-cosine phase operators (i.e. $\widehat{\textrm{exp}}(i\phi)=\... | g14226 | [
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0.001145978574641049,
... |
<p>I will formulate my question in the classical case, where things are simplest.</p>
<p>Usually when one discusses a continuous symmetry of a theory, one means a one-parameter group of diffeomorphisms of the configuration space $M$ which fix the action functional $S:P\rightarrow \mathbb{R}$, where $P$ is the space of... | g14227 | [
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0.00977211445569992,
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<p>Background:</p>
<p>It is well known that the quantum mechanics of $n$ identical particles living on $\mathbb{R}^3$ can be obtained from the geometric quantization of the cotangent bundle of the manifold $M^n = \frac{\mathbb{R}^{3n}-\Delta}{S_n}$, where $\Delta$ is the set of coincidences and $S_n$ is the permutatio... | g14228 | [
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0.0... |
<p>Centre of mass of a system cannot change its state of motion, unless there is an external force acting on it. Yet the internal force of brakes can bring a car to rest. Then what stops the car?</p> | g14229 | [
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<p>If an electron and positron are accelerated towards each other, at distances quite far away, there wouldn't be any significant electrostatic attraction, hence they need to be accelerated. But when they do come close, the Coulomb force is significant. So why do we accelerate the particle antiparticle pair, when they ... | g14230 | [
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<p>I do a bit of hobby programming and I often search the internet for little oddities that are fun to ponder over. I have read a few passages that try to explain quantum computing to the layman like myself. I have read of the <a href="http://en.wikipedia.org/wiki/Qubit" rel="nofollow">Qubit</a>, the more 'power' versi... | g14231 | [
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... |
<p>The maximum achievable probability of the Clauser-Horne-Shimony-Holt game is $\cos^2(\pi/8)\approx85.355\%,$ which can be proved with Tsirelson's inequality. But I don't imagine that this remained unknown until Tsirelson's 1980 paper. When was it first known that this constant is optimal?</p>
<p>I must admit&mdash... | g14232 | [
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0.062271248549222946,
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-0... |
<p>Lets put an ice cube on a fairly precise scale and take readings over a period of several hours. The ice cube is situated in a saucer so that the water is retained after melting. </p>
<p><strong>What will the recorded curve look like?</strong></p>
<p>Suppose ambients conditions: 25°C, RH40% and 1013 mbar.</p> | g14233 | [
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0.04440254345536232,
-0.01657017320394516,
... |
<p><img src="http://i.stack.imgur.com/Lnk3k.png" alt="enter image description here"></p>
<p>Could someone show the math behind it?</p>
<p>Source : "A vortex is a bunch of air circulating around itself. The axis around which the air is rotating is called a vortex line. It is mathematically impossible for a vortex lin... | g14234 | [
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<p>Consider force $F$ acting on a body of mass 1000kg and the displacement be $s$. So energy required to do so is $F$x $s$. Now consider the same force causing same displacement on body of mass 1kg. Here to energy required(according to equation) is same. But certainly more energy is required in the first case. How is ... | g14235 | [
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<p>Why is it that in <a href="http://en.wikipedia.org/wiki/Electro-osmosis" rel="nofollow">electro osmosis</a> the liquid will be attracted to the electrode having the same polarity sign as the one of the capillary walls but in <a href="http://en.wikipedia.org/wiki/Electrospray" rel="nofollow">electro spraying</a> the ... | g14236 | [
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0.04161... |
<p>A ferromagnet is attracted to a solenoid's magnetic field. I understand that now the ferromagnet produced a magnetic field, from that process is there an induced $EMF$? </p>
<p>Can ferromagnets that are not permanent magnets( i.e low magnetic remanence ) induced $EMF$ in the solenoid? </p> | g14237 | [
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<p>Suppose I have a pure magnetic dipole $\mathbf{\vec m} = m\hat z$ located at the origin. What is the magnitude of the field $|\vec B|$ as $r\to 0$? In other words, what is $\lim_{r\to 0}\frac{\hat{r}\cdot \vec{p}}{4\pi\varepsilon_0r^2}$? Is it just zero? $\infty$? Do I have to use some sort of quadripole term?</p> | g14238 | [
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-0.0435... |
<p>I am reading trough chapter one of Moshinsky's <a href="http://books.google.be/books?id=RA-xtOg4z90C&pg=PA20&dq=moshinsky%20harmonic%20oscillator%20states%20expressed%20in%20terms%20of%20creation%20operators&hl=en&sa=X&ei=ygilUeqQH-GP0AXrwoBo&ved=0CDoQ6AEwAA#v=onepage&q=moshinsky%20harmon... | g14239 | [
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<p>I'm solving an exercise about small oscillations and I have a doubt about coordinates that I have to use.</p>
<p>This is the text of the exercise:
"A bar has mass M and lenght l. Its extremity A is hooked to a coil (with lenght at rest $l_0$), its extremity B is hooked to the point O that is the origin of axes. "</... | g14240 | [
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-0... |
<p>What is the size of the magnetic dipole moment $\vec m$ of a superconducting diamagnetic sphere $radius=R$ in a uniform magnetic field $\vec B_0$? Since there is no free current, we can solve for $\Phi_m$, the scalar potential of $\vec H$.</p>
<p>The boundary conditions that I see are $r\to 0 \Rightarrow \Phi_m \lt... | g14241 | [
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<p>We have </p>
<ol>
<li>A point charge,</li>
<li>a homogeneously charged insulator with total charge $Q''$ which is a ball with radius $R$,</li>
<li>a conducting metal ball with charge $Q'$, radius $R$ and a grounded metal (no charge). </li>
</ol>
<p>The things I named are all separated by vacuum. I am supposed to i... | g14242 | [
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<p>The <a href="http://en.wikipedia.org/wiki/Gibbs%E2%80%93Duhem_equation" rel="nofollow">Gibbs-Duhem equation</a> states </p>
<p>$$0~=~SdT-VdP+\sum(N_i d\mu_i),$$ </p>
<p>where $\mu$ is the chemical potential. Does it have any mathematical (about intensive parameters) or physical meaning?</p> | g14243 | [
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<p>Why is the Higgs boson spin 0? Detailed equation-form answers would be great, but if possible, some explanation of the original logic behind this feature of the Higgs mechanism (e.g., "to provide particles with mass without altering their spin states") would also be appreciated.</p> | g14244 | [
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<p>Consider a (classical) system of several interacting particles. Can it be shown that, if the Lagrangian of such a system is Lorenz invariant, there cannot be any space-like influences between the particles?</p> | g14245 | [
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<p>I have a a coin infinitely thin, rotating along the diameter.
How to derive the formula for it's moment of inertia passing through the diameter.</p>
<p>I was suggested to use the surface density and infinitely small part of the surface area, equidistant from the axis of rotation (marked as $dS$ on the picture).</p>... | g14246 | [
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<p>I would like to clarify my understanding on why mass terms in Lagrangians of gauge theories are forbidden.</p>
<p>It's often repeated that particle masses are forbidden by electroweak symmetry because it is a chiral theory. I want to make a distinction between fermionic masses and gauge boson masses. </p>
<p>Looki... | g14247 | [
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<p>Just a question out of curiosity, what would happen if the event horizons of 2 black holes of the same mass were to come into contact? Would both gravitational accelerations be canceled where the event horizons overlap?</p> | g444 | [
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0.031849928200244904,
0.01266165915876627,
-0.06202463433146477,
0.00... |
<p>If the densities of the moon and the earth are related by $\rho_m / \rho_e =3/5$, and if $g_m /g_e = 1/6$,
then what is $R_m /R_e$? ($g=$ acceleration due to gravity and $R=$ Radius)</p> | g14248 | [
0.06617113947868347,
0.033736634999513626,
-0.026579612866044044,
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0.023346493020653725,
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0.03650560602545738,
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0.010471198707818985,
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0.01974639855325222,
0.04... |
<p>I am currently reading <a href="http://arxiv.org/abs/quant-ph/0108137" rel="nofollow">this</a> paper. I understand how the <a href="http://en.wikipedia.org/wiki/Bloch_sphere" rel="nofollow">Bloch sphere</a> $S^2$ is presented as a geometric representation of the observables of a two-state system:</p>
<p>$$ \alpha |... | g14249 | [
0.027257563546299934,
0.009583232924342155,
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0.04194575920701027,
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0.030982285737991333,
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-0.00011218198778806254,
-0.030190184712409973,
-0.0005067973979748785,
-0.028973298147320747... |
<p>If an heavy object (e.g. 10 tons) orbiting around Earth at 370 miles high, is connected with a cable back to Earth, we assumed either Earth is going to pull the mass or vice versa (or it will fall back to Earth). Assuming correct pressure/release/pull can be applied from the ground to prevent the fall, or it natural... | g14250 | [
0.012477589771151543,
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0.0028210156597197056,
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0.005070175509899855,
-0.010190718807280064,
... |
<p>I am reading an <a href="http://journals.aps.org/prb/abstract/10.1103/PhysRevB.74.115406" rel="nofollow">article</a> about <a href="http://www.google.com/search?as_q=floquet+bloch+state" rel="nofollow">Bloch-Floquet state</a>. My questions is in <em>Part II.B</em> and <em>Appendix A</em> of this paper, I will descri... | g14251 | [
0.015303763560950756,
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0.02667076140642166,
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0.033176884055137634,
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0.03014584258198738,
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... |
<p>$E$ = $mc^2$
And also
$E$ = $hf$ (f - frequency)</p>
<p>And hence Einstein said $m$ = $hf\over c^2$
And so photons have mass</p>
<p>But later he also said</p>
<p>$M$ = $M_0\over \sqrt {1-v^2/c^2}$ </p>
<p>Where if we put $v = c$ we get</p>
<p>$M = M_0/0 \leftrightarrow M=\infty$ </p>
<p>And so photon travelli... | g14252 | [
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0.004678435157984495,
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0.04183924198150635,
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0.012552919797599316,
0.014494230970740318,
-0.023255962878465652,
0.008974727243185043,
... |
<p>Is there any general purpose stellar evolution simulation engine or software? Something to throw in properties of the star and to watch how (and why) they change along the timeline - with or without visualization (but preferably with).</p>
<p>The best of what I have found on the net is this site:</p>
<p><a href="h... | g14253 | [
-0.007201785687357187,
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0.0... |
<p>Consider a yield-stress liquid in gravity. I assume that the buyouncy of a small gas-bubble will not be enough to overcome the yield stress (so the liquid doesn't behave liquid), thus leaving the bubble trapped. Is this so in theory, or is there a flaw in my thinking?</p>
<p>Sme argue that there are no yield-stress... | g14254 | [
-0.01462414488196373,
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0.057657934725284576,
0.023813389241695404,
... |
<p>The ideia is to show that, because of Goldstone modes, 2d systems are quite different from 3d ones. So, considering the Heisenberg model, I'll post here what I'm asked to and my current thoughts on the subject in hope you can give me further assistance.</p>
<p><strong>1. fluctuations on Heisenberg model should dest... | g14255 | [
-0.013026322238147259,
0.009356042370200157,
0.006762505508959293,
-0.0138535862788558,
0.018114333972334862,
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0.027525003999471664,
0.006729274056851864,
0.... |
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