question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>In the demonstration of the Clausius theorem in classical thermodynamics my book uses the fact that $Q_{net}\le0$ is negative in a cyclic monotherm (meaning with one heat reservoir) transformation. This fact, however, left me a bit uneasy. Taking, as usual, a Carnot cycle as an example, and calling the adiabatic and... | g13977 | [
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<p>What I read is that a speaker produces sound by the movement of a coil attached to a cone which moves back and forth. So, If I try to move the coil by hand, would it produce sound? If not, why? or Why would it produce sound only when the current moves the coil?</p> | g13978 | [
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<p>1-In QM every observable is described mathematically by a linear Hermitian operator. Does that mean every Hermitian linear operator can represent an observable?</p>
<p>2-What are the criteria to say whether some quantity can be considered as an observable or not?</p>
<p>3-An observable is represented by an operato... | g13979 | [
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<p>A string has a mass per unit length of 9 10–3 kg/m. What must be the tension in the string if its second harmonic has the same frequency as the second resonance mode of a 2m long pipe open at one end? The length of the string is 1.5 m.</p>
<p>this is my solution</p>
<p><a href="http://screensnapr.com/e/u4kvtH.png"... | g13980 | [
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<p>If someone knows how identify hue, brightness, and chroma of color, please let me know.</p>
<p>I am a PhD student at Educational Linguistics UNM.</p> | g13981 | [
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<p>What is the Jost function in scattering theory? Is it an operator or some kind of determinant? How is it obtained?</p> | g13982 | [
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<p>More simply a tensor algebra question, but in General relativity I have the following when I calculate $\Gamma_{00}^\lambda$:-</p>
<p>$$
\Gamma_{00}^\lambda = \frac{1}{2}g^{\nu\lambda}\left(
\frac{\partial g_{0\nu}}{\partial x^0} +
\frac{\partial g_{0\nu}}{\partial x^0} -
\frac{\partial g_{00}}{\partial x^\nu}
\rig... | g13983 | [
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<p>Here in this forum (and elsewhre) I read about "charged" black holes.
What is the background for this questions? Is this more a question of
theroretical interest?</p>
<p>In "practice" :=) black holes should be neutral, because matter
is neutral globally. A star is charged a little bit, depending
on surface temp... | g13984 | [
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<p>Let's have hamiltonian
$$
H(\psi , P ,\partial_{i}\psi ) = P\partial_{0}\psi - L(\psi , \partial_{\mu}\psi ), \quad P = \frac{\partial L}{\partial (\partial_{0}\psi)}. \qquad (.0)
$$
I tried to introduce generating function for it. It will be easy if hamiltonian would be covariance,
$$
H = P^{\mu}\partial_{\mu}\psi ... | g13985 | [
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<p>I am learning the <strong>Magnetic Effects of Electric Currents</strong> at school, and I was given an equation. I was told it would be elaborated on next year. But since I can't seem to bring myself to wait, here it is:</p>
<blockquote>
<p>B = µ<sub>o</sub>I/2πr</p>
</blockquote>
<p>Now, <strong>µ<sub>o</sub></... | g13986 | [
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<p>Imagine an EM wave impinging on a metal. Fresnel's formulas tell us that no wave can propagate through the metal, or that the transmitted field is an evascent wave with some penetration depth dependent on the refraction index of the metal. </p>
<p>If we now would like to zoom into the microscopic physics of the ref... | g13987 | [
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<p>My Friend gave me a question today. The question was.::</p>
<blockquote>
<p>We have a point A. At a distance of $x_0$ from the point. There is a particle$(P_1)$. Also, a particle is present at the point A $(P_2)$.The Particle $P_1$ moves with a velocity of $u_1$ towards Point A. At the same instant the particle $... | g13988 | [
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<p><a href="https://www.youtube.com/watch?v=KeGidtk6t2Y" rel="nofollow">Videos like this</a> show a form that suggests a radial symmetry in the gas jet. The same is reinforced by <a href="http://www.aerospaceweb.org/question/propulsion/shock-diamonds/overexpansion.jpg" rel="nofollow">schematic illustrations</a>.</p>
... | g13989 | [
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<p>Lets say I have a strong halogen light source which has a lot of IR radiation (e.g. a construction lamp).</p>
<p>If I change the transparent front glass from the enclosure with a IR filter that blocks visible light, what will it do with the heat inside the enclosure?</p> | g13990 | [
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<p><a href="http://en.wikipedia.org/wiki/Gravitational_wave" rel="nofollow">Gravitational waves</a> just have a little interaction with other particles. How can we detect such little influence on mass?</p> | g13991 | [
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<p>Helicopters or dual/quadcopters stop rising after reaching some height from the ground. What causes that? And what one should do if he want to prevent this, if he want the helicopter to keep rising up?</p> | g435 | [
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<p>While reading about <a href="http://en.wikipedia.org/wiki/Dielectric_heating" rel="nofollow">dielectric heating</a> on Wikipedia, I read about the ion drag mechanism but there wasn't enough information about.</p>
<p>I know there is another Phys.SE <a href="http://physics.stackexchange.com/q/23064/2451">question</a>... | g13992 | [
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<p><img src="http://i.stack.imgur.com/dUapj.png" alt="enter image description here"></p>
<p><img src="http://i.stack.imgur.com/3dGdQ.png" alt="enter image description here"></p>
<p>My problems:</p>
<ol>
<li><p>I know that when a person is moving away, the perceived frequency will be lower than the frequency of the s... | g13993 | [
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<p>We had to measure the resistance of $R_x$, we balanced the <a href="http://en.wikipedia.org/wiki/Wheatstone_bridge" rel="nofollow">Wheatstone bridge</a> and did calculations. My question is: we didn't include galvanometer error into calculations. Why is that? I read that it's very precise, but that doesn't seem like... | g13994 | [
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<p>I've only a general grasp on how all this works, so it could be I'm asking this poorly or misunderstanding what happens. With that said:</p>
<p>The energy of EM radiation is a function of its frequency. With enough energy (a high enough frequency) I understand it's possible to knock an electron out of its orbit(al)... | g13995 | [
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<p>Given that the gluino is in the same representation of SU(3) that the gluon and so the same kind of interaction vertexes with quarks, I guess that it could have a role in the strong force. But there are obvious differences: being a fermion, there is no a classical field, and as you can not accumulate fermions in the... | g13996 | [
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<p><a href="http://imgur.com/KRhpgF2" rel="nofollow"><img src="http://i.imgur.com/KRhpgF2.png" title="Hosted by imgur.com" /></a></p>
<p>Can anyone explain why they say Doppler effect does not depend on acceleration?</p>
<p>Would having acceleration not affect the frequency?</p>
<p>If the source emits the first circ... | g13997 | [
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<p>Anyone who has taken high school physics has seen the following assembly. You drop one ball from the left hand side and the ball from the farthest right hand side gets knocked away. This is to illustrate the conservation of momentum and energy.</p>
<p><img src="http://i.stack.imgur.com/yXEun.png" alt="enter image d... | g13998 | [
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<p>Suppose I have some classical field equation for two photon fields with amplitudes $A_1(z),A_2(z)$ (plane waves) given as</p>
<p>${A}_1=\alpha f(A_1,A_2) \\
{{A}_2}=\beta g(A_1,A_2) $</p>
<p>Under what conditions can I make the replacement $A\rightarrow \hat{A}$ ? I am uncomfortable with the Bohr correspondence... | g13999 | [
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<p>The pulse tubes are really loud. We've wrapped the helium lines in sound absorbing foam, and we have a cage around the top of the cryostat also lined with foam, but it's still pretty loud. Are there any really good and practical ways to damp the sound?</p> | g14000 | [
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<p>I'm a beginning graduate student, and I have 2 years before I have to pick a specialization. I would like to know which areas of physics call for the most intuition or physical insight. If this sounds like too vague a question, let me give an example. </p>
<p>See the problem below:
"A rubber band with initial leng... | g14001 | [
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<p>I have some real measurements from a process and I happened to look at the mutual distribution of (x(t), xdot(t)). I found that they seem to follow 2d normal distribution around (mu, 0). See image, the y-axis is xdot.</p>
<p><img src="http://i.stack.imgur.com/rQfWk.png" alt="x-xdot-histogram"></p>
<p>Is there some... | g14002 | [
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<p>If an electron is a wave, what is waving? </p>
<p>So many answers on the internet say "the probability that a particle will be at a particular location"... so... the electron is a physical manifestation of probability? That doesn't sound right. </p>
<p>This page <a href="http://mwolff.tripod.com/see.html">http://m... | g1 | [
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<p>Is "existence of cosmic dark energy" <a href="http://en.wikipedia.org/wiki/Falsifiable" rel="nofollow">falsifiable</a> yet? And what about dark matters? Let me rephrase it again(pardon me for my previous poor expression)-</p>
<p>Is there any condition discovered which can be used to determine the "existence of cosm... | g14003 | [
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<p>as there's so many papers on the opera result and it's a struggle flicking through them all combined with my limited knowledge meaning I cannot well differentiate silly nonsensical papers from ones with much more substance; could anybody sum up for me what papers or theories put forward which could decently explain ... | g14004 | [
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<p>Could someone help me solve this probably not very hard problem?</p>
<p>Given Lagrangian Density:</p>
<p>$\mathcal L=\bar{\psi}(i\gamma^\mu\partial_\mu-g\gamma^5\phi)\psi+\frac{1}{2}(\partial_\mu\phi)(\partial^\mu\phi)-\frac{1}{2}m^2\phi^2$</p>
<ul>
<li>Find the equations of motion for the wave-functions $\psi$ a... | g14005 | [
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0.07541538774967194,
0.0027617199812084436,
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0.02955682761967182,
-0.04323721304535866,
0.007719798944890499,
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0.04066040739417076,
-0.033621061593294144,
-0.0162... |
<p>The partition function of the grand canonical ensemble can be generally stated as
$$ \mathcal{Z} = \sum_{r} e^{-\beta(E_{r} - N_r\mu)}\tag{1}$$
where $E_{r}$ is the energy of the micro-state $r$ of $N_r$ particles, $\beta$ the usual inverse temperature, and where $\mu$ is the chemical potential. </p>
<p>This is no... | g14006 | [
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<p>The standard picture of the nucleus of atom is that is several distinct nucleons, which themselves are composed of quarks. However, it seems to me like a much simpler picture is that the nucleus is directly made out of quarks, without having nucleons as substructures. That is, that the nucleus is the ground state of... | g14007 | [
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<p>Many times I heared that the solar wind consists of protons and alpha particles. The both are positively charged, but are there electrons in solar wind?</p> | g14008 | [
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<p>I am looking at a coupled plane pendulum problem where the pendula are identical with mass $m$ and length $r$, and connected by a spring with spring constant $k$ and an equilibrium seperation $d_0$. If $\theta_1$ and $\theta_2$ are the angular displacement with the vertical then in these coordinates then the Lagrang... | g14009 | [
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<p>I was reading about concept of <a href="http://en.wikipedia.org/wiki/Effective_mass_%28solid-state_physics%29" rel="nofollow">effective mass</a> on Wikipedia and came across the line that effective mass of a particle can be negative and even zero. How is this possible?</p> | g14010 | [
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<p>From my knowledge, a big mass (planet star etc) can bend the fabric of <a href="http://en.wikipedia.org/wiki/Spacetime" rel="nofollow">spacetime</a>. Is there a formula that we can use to work out how much it bends?</p> | g14011 | [
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<p>In explaining/introducing second-order phase transition using Ising system as an example, it is shown via mean-field theory that there are two magnetized phases below the critical temperature. This derivation is done for zero external magnetic field $B=0$ and termed spontaneous symmetry breaking The magnetic field i... | g14012 | [
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<p>I am looking at a question from University Physics</p>
<p><img src="http://i.stack.imgur.com/loQo7.png" alt="enter image description here"></p>
<p>The given answer</p>
<p><img src="http://i.stack.imgur.com/cgP7p.png" alt="enter image description here"></p>
<p>Whats the intuition behind using the below diagram </... | g14013 | [
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<p>I'm working on ray tracing and I'm trying to understand the impact of the angle at which a light-path intersects the surface of a light source on the amount of light that source delivers to the path (per unit time, of course).</p>
<p>My assumption for an ideal diffuse light source is that light rays leaving a parti... | g14014 | [
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<p>In Thomas Andrew's experiment, consider the dome shaped saturation region. If we increase the pressure at constant volume until we reach the critical point, why does the density of vapours rise and the density of liquid fall? Moreover, why will the meniscus or the separation boundary of two phase slowly become less ... | g14015 | [
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<p>We experience space and time very differently. From the point of view of physics, what fundamentally grounds this difference?</p>
<p>Dimensionality (the fact that there are three spatial dimensions but only one temporal) surely cannot be sufficient, as there are tentative proposals among string theories for models ... | g14016 | [
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<p>The tensorial form of Hooke's law for the strain-stress relationship in a crystal is (in the Voigt notation):</p>
<p><img src="http://i.stack.imgur.com/wrorL.png" alt="Hooke's law"></p>
<p>where $\sigma$ is the strain, $\epsilon$ is the stress and C is the stiffness tensor:</p>
<p><img src="http://i.stack.imgur.c... | g14017 | [
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... |
<p>I've been looking for some straightforward method or trick to obtain the transfer functions of active filters (like the <a href="http://en.wikipedia.org/wiki/Sallen%E2%80%93Key_topology" rel="nofollow">Sallen-Key</a> filter, the butterworth or Cauer topology etc...) since KCL or KVL requires a lot of algebraic manip... | g14018 | [
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<p>No doubt I am wondering about the Young's double slit phenomena. If we observe or measure the properties of a subatomic particle, we are able to know its mass, velocity and it comes to existence. So is it true for our natural world? Like we all the form of wave functions and when we interact with an object with our ... | g14019 | [
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0... |
<p>Is there a site that allows you to give the approximate specs of a set of magnets and then it produces the graph of the magnetic field for you?</p>
<p>Here is a situation I try to understand:</p>
<p>I have a set of rectangular magnets about 1*0.75*.25 inches with north and south on large faces. The magnets are glu... | g14020 | [
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-... |
<p>Anyway what I am trying to figure out is something I have been thinking about for many years. The dinosaurs didn’t die from a big
explosion or anything just that the earths gravity increased and made them less competitive to smaller creatures. I have heard bone mass decreases
for astronauts so I am think it must in... | g14021 | [
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0.0... |
<p>We are familiar with the grand partition function for the grand canonical ensemble. This makes me wonder: what kinds of modifications would be required if the particles interacted?</p>
<p>Thanks.</p> | g14022 | [
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0.... |
<p>Imagine spaceship in vacuum with mass = 1. At beginning, it has velocity 0, and kinetic energy 0. </p>
<p>$$W_1 = 0$$</p>
<p>Then, it turns on its engine, and changes velocity from 0 to 20 (delta v = 20). It's kinetic energy became:</p>
<p>$$W_2 = \frac{1}{2}mv^2 = \frac{1}{2}\times 1\times 20^2 = 200$$</p>
<p>$... | g436 | [
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0.051497187465429306,
0.050920... |
<p>I want to start off by saying that I've looked around for other explanations, but I've not really found any satisfying ones. My question is basically the whole "Why can anything move at all?" question, with a little twist. Refer to this picture:</p>
<p><img src="http://i.stack.imgur.com/bmhkv.png" alt=""></p>
<p>N... | g14023 | [
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0.01485... |
<p>The fine structure constant $\alpha$ actually is speed parameter of electron $\beta_e$, moving around proton in hydrogen atom. </p>
<p>$v_n=\frac {\alpha_c}{n}=c\frac {\alpha}{n}=c\frac {\beta_e}{n}$</p>
<p>How can it be a constant!?</p>
<p><img src="http://cac07science.wikispaces.com/file/view/atom.jpg/32645403/... | g14024 | [
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0.009097318165004253,
0.027572665363550186,
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0.00... |
<p>Can the following groups of components of metric tensor can assigned a clear sense?</p>
<p><img src="https://docs.google.com/drawings/pub?id=1kVqkN1gT-a2fDy2S851l9iQKaMfaatCDo517OSZBHEo&w=467&h=228"></p>
<p><a href="https://docs.google.com/drawings/pub?id=1kVqkN1gT-a2fDy2S851l9iQKaMfaatCDo517OSZBHEo&w=... | g14025 | [
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<p>I'm stuck in a small calculation. I try to solve a small exercise.</p>
<p>You should calculate for a given entropy the Gibbs free energy, where the entropy is given as</p>
<p>$S\left(U,V\right) = \frac{4}{3}\left(\alpha V U^3\right)^{1/4} \qquad\dots\qquad U$ is the internal energy, $V$ is the volume and $\alpha &... | g14026 | [
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<p>Modern car designs have a crumple zone that absorbs most of the impact in a collision, and a strong "safety cell" in the passenger compartment that protects the passengers. These designs are put to the test in crash tests.</p>
<p>Currently there are two ways frontal crash tests are performed, a full-wrap frontal co... | g14027 | [
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<p>I need to calculate the force of a weight bearing down on a smaller object, constraining it from expansion.</p>
<p>The weight bearing down has a much bigger surface area than the smaller object.</p>
<p>I know the mass of the weight.</p>
<p>I know the surface area of the smaller object.</p>
<p>What else do I need... | g14028 | [
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<p>Let's say I have a parallel plate capacitor.</p>
<p>How would I find the electric field at a certain point INSIDE the capacitor (inside the dielectric let's say). From what I understand, the flux of the electric field will be constant everywhere (even if there is more than 1 different dielectric), but the electric ... | g14029 | [
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<p>The <a href="http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment" rel="nofollow">Michelson-Morley experiment</a> seems to have taken many years, resources and a nervous breakdown to complete.</p>
<p>Is it possible to recreate a variation of this experiment at home for say, under $1000, given the techno... | g14030 | [
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... |
<p>I am dealing with quantum harmonic oscillator.</p>
<p>In every single book or video i have checked out i can read how the mathematical technique for solving this <a href="https://en.wikipedia.org/wiki/Schr%C3%B6dinger_equation" rel="nofollow">Schrödinger equation</a>: </p>
<p>$$
W\psi = - \frac{\hbar^2}{2m} \frac... | g98 | [
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0.024980822578072548,
... |
<p>This comes from the <em>Interference of Photons</em> section in the book <em>The Principles of Quantum Mechanics</em> by P Dirac:</p>
<blockquote>
<p>We shall discuss the description which quantum mechanics provides of the interference. Suppose we have a beam of light which is passed through some kind of interfer... | g14031 | [
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... |
<p>When a charged particle gets accelerated it emits electromagnetic waves. In reality, when a charged particle gets accelerated the electric field around the charge remains unchanged, but the magnetic field changes. Here the energy provided to the particle - by the energy source accelerating it - gets divided into the... | g437 | [
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<p>We can define a probability distribution over phase space (say 1D) $\rho(x,p)$ such that, for example,
$$\langle x\rangle = \int x \rho(x,p) dxdp$$ etc.</p>
<p>It can be shown <a href="http://en.wikipedia.org/wiki/Liouville%27s_theorem_%28Hamiltonian%29" rel="nofollow">here</a> that such a distribution satisfies (a... | g14032 | [
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0.0... |
<p>Consider for instance the <a href="http://en.wikipedia.org/wiki/Quantum_electrodynamics#Mathematics" rel="nofollow">QED Lagrangian</a>. Is it possible to compute the rate of virtual electron-positron creation from the vacuum?</p> | g14033 | [
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0.00991700... |
<p>We think that the electric field and gravitational field operate similarly with their corresponding charges/masses. With just a difference that the electric field is sometimes attractive and sometimes repulsive. </p>
<p>Now I have read that when a charged particle moves the electric field lines associated with it, ... | g14034 | [
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<p>Silly thought.</p>
<p>A transducer, by definition, is a device that converts variations in one form of energy to another. An electric lamp converts electricity into visible light - the brightness may vary depending upon the electric potential applied. </p>
<p>Is it correct to state an Electric Lamp is a transducer... | g14035 | [
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<p>In a Tunneling problem, if the $E_o<V$, we can show that the scattering wavefunction inside a rectangular barrier is a decaying exponential. The solution being real implies that the probability current $J$ is zero at every point inside the barrier.</p>
<p>From equation of continuity,</p>
<p>$\frac{\partial|\psi... | g14036 | [
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<p>I'm on a thread of interest in the precise physics that allow the creation of the computing process. It began as a question posted in search of an understandable explanation of what physical form exactly does the code instruction information take on a hard drive that <em>instructs</em>, and thus allows, a computer t... | g14037 | [
0.011983905918896198,
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<p>I want to know what properties of steam make it the fluid of choice in</p>
<ol>
<li><p>steam turbines</p></li>
<li><p>jet ejectors.</p></li>
</ol>
<p>I want to understand the mechanism of energy conversion in these equipment and hence understand why steam is the preferred choice. Please leave out economic factors ... | g14038 | [
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<p>I am reading the book "The man they wouldn't let die" by Alexander Dorozynski, which is an biography of Russian theoretical physicist Lev Landau, and I have encountered this passage</p>
<blockquote>
<p>Absolute zero is considered as the lowest possible temperature for any element: $-273.16^{\circ}$ C. It was long... | g14039 | [
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<p>If electrons and photons, and possibly more particles, exhibit dual character, why don't physicists create a new classification for them? Why describe them as both waves and particles. Why not rather create a new classification, which accurately describes their behavior? </p> | g14040 | [
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<p>I choose to post this question on the physics exchange seeing there would be a bigger audience for answers than the astronomy exchange still in BETA.
But i'm looking to buy a telescope and was wondering what i could see with a 114mm Aperture 675x Zoom Telescope? The type of things would be interested in would be ou... | g14041 | [
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<p>Imagine that I use a long wire to create an electromagnet. Let's also assume that the current flowing along the wire is constant, and that the wire is winded on the vacuumm.</p>
<p>Is the magnetic field generated by this electromagnet (current flowing over an arbitrary path on a finite volume) proportional to the c... | g14042 | [
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<p>I'm teaching myself quantum information theory using Nielson and Chuang's "Quantum Computation and Quantum Information" and I'm at a point in the book where the formalism is starting to make my eyes bleed. </p>
<blockquote>
<p>Exercise 2.56 Use the spectral decomposition to show that $K \equiv -i\log(U)$ is Hermi... | g14043 | [
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<p>I have a raw material which melts at $96\ ^\circ C$. My aim is to make water content evaporate at temperature below this temperature.
I can apply vaccume oven for this. I want to know at what pressure the water evaporates by keeping low temperature so that the material doesn't melt.</p> | g14044 | [
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<p>When looking at the band diagram of a semi-conductor, direct conclusion of the invariance under discrete translations, for a filled state with an electron, one does know precisely it's momentum, so my question is: does it imply, by Heisenberg, uncertainty that this electron is spread over the whole lattice? Is it th... | g14045 | [
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<p>I observed that when I keep constant distance between object and lens but I move my eye, I get different magnification. When I am closer to lens I can see large image of the object. But if I go away from the lens I can see inverted image.</p>
<p>So while making my own binocular/telescope (for practical purpose only... | g14046 | [
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<p>I watched "Apollo 13" yesterday, and they had the "angle-of-attack" problem that had to be manually solved, to prevent the ship from "<em>ricochet[ing] off the atmosphere like a rock skipping off a pond</em>".</p>
<p>I found and read <a href="http://boards.straightdope.com/sdmb/showthread.php?t=562456" rel="nofollo... | g14047 | [
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<p>How can <a href="http://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws" rel="nofollow">KVL (Kirchhoff's Voltage Law) & KCL (Kirchhoff's Current law)</a> be derived from Maxwell equations in lumped circuits?(Lumped network : if $d$is the largest dimension of the network and $\lambda$ is the wavelength of the si... | g14048 | [
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<p>Imagine that you have a triangle where each side has the length $a$ and a charge $q$ sitting at every vertex. Additionally, we have a charge $-3q$ sitting in the center of the triangle. What is the first non-vanishing multipole moment?</p>
<p>I thought that there cannot be a net charge or dipole moment, but I was u... | g14049 | [
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<p>The state </p>
<p>$$|\psi\rangle ={1\over \sqrt 2}(|+\rangle|-\rangle-|-\rangle|+\rangle)$$ </p>
<p>of system made up of 2 spin-$1\over 2$ particles is invariant under the operator</p>
<p>$$\exp{i\theta S_y}.$$</p>
<p>What implications/relations does this have relating to the angular momentum properties of the s... | g14050 | [
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<p>According to Pauli’s exclusion principle, $s$ orbital contains at most two electrons with the opposite spin(up and down). Why can't $s$ orbital contain a third electron whose state is the linear combination of spin up and down?</p> | g14051 | [
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<p>I'm sure you have tried sometime to make a sound by blowing in an empty bottle. Of course, the tone/frequency of the sound modifies if the bottle changes its shape, volume, etc. </p>
<p>I am interested in understanding how the tone/frequency of this sound can be (approximately) calculated from the shape of the bott... | g14052 | [
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<p>When Current passes thru a spring , some books mention that it gets compressed.
However, I think due to the heating effect of current, molecules will increase kinetic energy and the spring should get elongated. What is the physical mechanism for the compression instead of elongation?</p> | g14053 | [
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<p>If a ball is simply dropped, each time a ball bounces, it's height decreases in what appears to be an exponential rate. </p>
<p>Let's suppose that the ball is thrown horizontally instead of being simply dropped. How does the horizontal distance travelled change after each bounce?</p>
<p>Context behind question: ... | g14054 | [
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<p>I would be very happy if someone could take a stab at conveying what conformal blocks are and how they are used in conformal field theory (CFT). I'm finally getting the glimmerings of understanding from reading <a href="http://www.physics.rutgers.edu/~gmoore/MooreReadNonabelions.pdf">Moore and Read's</a> wonderful p... | g14055 | [
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<p>At least from their names, it seems motional emf is induced, so what's the difference?</p> | g14056 | [
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<p>Many experiments, such as optical, superconductivity, etc, use the samples that involve rare earth metals and transition metals. Why are they used that often. Is the main reasons:</p>
<ol>
<li>They have the required electronic structure in its d- and f- orbital so that we can create the required spin-spin interacti... | g14057 | [
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<p>Where do you check and put them usually?
Let's make a wiki ~</p> | g14058 | [
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... |
<p>Is there any thing that will cause spacetime to expand, so that particles are pushed away from them rather than pulled towards it. I know things such as black holes and planets causes dips and curve in spacetime, but is it possible that a celestial object will stretch spacetime?</p> | g14059 | [
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<p>I wonder if anyone can advise me literature about "long string model" of black hole. I've tried <a href="http://www.google.com/search?as_q=%22black+hole%22&as_epq=long+string" rel="nofollow">Google</a>, and of course <a href="http://search.arxiv.org:8081/?query=%22black+hole%22+%22long+string%22&in=" rel="n... | g14060 | [
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-0.... |
<p>According to Reisnick and Halliday, retardation is the acceleration in the negative direction of time axis ie. opposite to the motion. Decreasing accleretion is the decrease in the magnitude of time rate of change of velocity. Am I correct or not? What is the $v$-$t$ graph with retardation and decreasing acceleratio... | g14061 | [
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<p>Why does ${\Delta}S_{m(fusion)} = \frac{{\Delta}H_{m(fusion)}}{T}$ ?</p>
<p>I always thought ${\Delta}S = \frac{dQ}{T}$</p>
<p>In this case does it mean $dQ = {\Delta}H$ ??</p>
<p>Why is it so?</p> | g14062 | [
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<p>If you try to integrate the solution of the potential step,</p>
<p><a href="http://en.wikipedia.org/wiki/Solution_of_Schr%C3%B6dinger_equation_for_a_step_potential#Solution" rel="nofollow">http://en.wikipedia.org/wiki/Solution_of_Schr%C3%B6dinger_equation_for_a_step_potential#Solution</a></p>
<p>you will notice th... | g14063 | [
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<p>In their last homework, some of my students miscalculated a charge to be $10^{20}$ C over a squared meter and I was wondering if there was as much positive charges in the entire Universe. It would do the trick if I could simply estimate the total number of protons (including those in nucleus) in the entire Universe ... | g14064 | [
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0.0... |
<p>A person is standing on a weighing scale in an elevator in upward acceleration.</p>
<p>Let $N$ be normal reaction force exerted by the weighing scale to the person (upward).</p>
<p>It is known that the person will experience a normal reaction force ($N$) larger than his own weight (larger reading on the weighing s... | g14065 | [
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0.0287587... |
<p>Some quantum erasure experiments involve polarization of photons. In one such experiment with a double slit, a horizontal polarizer is used in front of one slit, and a vertical polarizer is used for the second slit and the idea is that then horizontal or vertical polarization of the photon coming out of the double s... | g14066 | [
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<p>I'm reading about Quantum Monte Carlo, and I see that some people are trying to calculate hydrogen and helium energies as accurately as possible.</p>
<p>QMC with Green's function or Diffusion QMC seem to be the best ways to converge on the "exact" solution to Schrodinger's equation.</p>
<p>However, if one wants to... | g14067 | [
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<p>How do I find the angular momentum of a body about any point?<br>
We know that $L=I\omega$ for a body rotating in space, where $L$ denotes the angular momentum, $I$ denotes the moment of inertia and $\omega$ denotes the angular velocity. However, this is <strong>only applicable</strong> for <strong>Fixed Axis of Rot... | g14068 | [
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<p>I am a physics undergrad and thinking of exploring quantum information theory. I had a look at some books in my college library. What area in QIT, is the most mathematically challenging and rigorous? From what I saw in the books, most topics was just simple linear algebra. I am looking for an area which is mathemati... | g14069 | [
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<ol>
<li>Is there any physics theory that either groups together gravity and dark energy/dark matter or eliminates dark energy/dark matter by modifying standard understanding of gravity or any force? If so, is there any theory that still matches with all correct predictions of standard physics theories?</li>
</ol> | g14070 | [
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<ol>
<li><p>Does quantum field theory accept gravitational wave? As quantum field theory is flat spacetime theory, I wonder whether gravitational wave would be true.</p></li>
<li><p>Does contemporary string theory variants accept gravitational wave?</p></li>
</ol> | g14071 | [
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0.02... |
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