question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>Hello again question board.
I'm in need of some help with my b) question for homework I have. Following question is verbatim:</p>
<p>"How thick should a wall of shielding iron be to absorb a 10 GeV/c pion beam. Use the PDG table and the lecture notes to find the necessary parameters. a) Compute the thickness if the... | 2,249 |
<p>I have several doubts about solving circuits.</p>
<ol>
<li>Can any circuit be solved using <a href="http://en.wikipedia.org/wiki/Nodal_analysis" rel="nofollow">Nodal Analysis</a>?</li>
<li>If some circuit can be solved using Nodal Analysis, can it be solved using Mesh Analysis too?</li>
<li>Why do we need these tec... | 2,250 |
<p>I need a nudge in the right direction, i guess (this is not a homework question).</p>
<p>I want to calculate the total length of a ray from an emitter to a target which passes through a slab with known properties.</p>
<p>Given:</p>
<ul>
<li>Position of Emitter and Target $P_\text{Source}, P_\text{Dest}$</li>
<li>... | 2,251 |
<p>A satellite at 8000 km from Earth where gravity is 6.4 m/s^2. What is the velocity of satellite? I don't the formula to find speed of satellite.</p> | 2,252 |
<p>We want to study the magnetic field at point $P$. So, from the figure we take that:</p>
<p><img src="http://i.stack.imgur.com/xWx3I.png" alt="enter image description here"></p>
<ol>
<li>$\oint_{L_1} B\cdot dl=\mu_0 I_1$</li>
<li>$\oint_{L_2} B\cdot dl=\mu_0 I_2$</li>
<li>$\oint_{L_3} B\cdot dl=\mu_0 I_2$</li>
</ol... | 2,253 |
<p>It is difficult to imagine the infiniteness of space and how it itself is expanding rather than the universe expanding into something else. A helpful analogy is that of drawing little dots (representing galaxies or some other sub-universal structure) onto a deflated balloon and then blowing it up. The surface expa... | 2,254 |
<p>Animals that have an eye on each side of their head have 360 degree vision so just like with the inverted vision glasses you can buy I'm wondering how you make 360 degre e glasses?
I'm thinking of a half periscope setup with a lense on the end on each eye.</p> | 2,255 |
<p>I have situation where I am simulating discrete time quantum walk (DTQW) for various graphs. I have two quantum walkers on the graph and they can interact with each other by the fact that where the two walkers are co-located on the same node of the graph a relative phase can be introduced.</p>
<p>I then measure the... | 2,256 |
<p>An ergodic dynamical system $(\Omega,\phi^t,\mu)$ is such that the time average $\bar{f}$ of every function $f\in L_1(\Omega,\mu)$ equal the <em>space</em> average $\langle f \rangle_\mu$, i.e. the system densely cover all the phase space ($\mu$-almost everywhere). Another equal condition of ergodicity is that the o... | 2,257 |
<p>The graph below (see attached) shows the measured magnetization against temperature at room pressure for the material Gd and for another material for use in a magnetic refrigerator at room temperature.</p>
<p>1)Calculate the expected change of temperature of a thermally isolated piece of Gd when the field in which ... | 2,258 |
<p>Gravitational attraction and electrostatic attraction/repulsion are intrinsic properties of matter, any particle (electron, proton) for some unknown reason can produce KE at a distance.</p>
<p>But magnetic attraction/force is not an intrinsic property of matter, a charged particle generates a magnetic field/flux an... | 2,259 |
<p>When there is a wave, something is undulating. In the example of a rope, the rope is what undulates. In the case of a ripple on a pond, the water is undulating, and when a sound wave propagates, the air is undulating. The question is: in the case of a particle, what undulates?</p> | 2,260 |
<p>Say you want to calculate degree of ionization for different gases in atmosphere of a star with abundances similar to those in Sun (let's assume you only have hydrogen, helium and sodium) over the temperature range (from 2000 K to 45000 K for example) using Saha equation: </p>
<p>$$\frac{n_{i+1}}{n_i}=\frac{g_{i+1}... | 2,261 |
<p>When you spray gas from a compressed spray, the gas gets very cold, even though, the compressed spray is in the room temperature.</p>
<p>I think, when it goes from high pressure to lower one, it gets cold, right? but what is the reason behind that literally?</p> | 2,262 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/3081/why-cant-a-piece-of-paper-of-non-zero-thickness-be-folded-more-than-n-times">Why can't a piece of paper (of non-zero thickness) be folded more than "n" times?</a> </p>
</blockquote>
<p... | 41 |
<p>It is known that all observers will agree on the position of the black hole event horizon. But what about the cosmic horizon of the de Sitter space? Can one say that the horizon of scientist1 is different from the horizon of scientist2?</p>
<p>If so, it turns out that the scientists are researching different univer... | 2,263 |
<p>I'm new here. I have a (maybe dumb) question: What are <a href="http://www.google.com/search?as_q=nonlinear+capacitor" rel="nofollow">non-linear capacitors</a>? I'm given a circuit including a capacitor and the question says </p>
<blockquote>
<p><em>The given capacitor is non-linear with the characteristic equati... | 2,264 |
<p>Wolfram as well as Aldrovandi and Freitas <a href="http://arxiv.org/abs/physics/9712026" rel="nofollow">1</a> maintain that iterated functions $f^t(x)$ are a valid alternative to PDEs for modelling physics. Instead of just citing <a href="http://arxiv.org/abs/physics/9712026" rel="nofollow">1</a>, I want to be able ... | 2,265 |
<p>I have unitary matrix and I would find the quantum circuit associated. There are 3 qubits input so it's a 8x8 matrix but it's not a simple operation. The number of gates is not specified. </p>
<p>Is there a universal method ? Matrix decomposition with a software ?</p>
<p>Thank you!</p> | 2,266 |
<p>Different frequencies of light travel at different speeds through solids, which along with Snell's law allows for rainbows. Has this phenomenon of variable speeds been predicted through derivations? What does it tell us about the interactions that occur when light travels through a solid?</p> | 2,267 |
<p>Erm. This question got shot-down in electronics.stackexchange.com and somebody recommended I raise it on here, so ... </p>
<p>Do metals with the property of strong diamagnetism also exhibit inductance?
Would a fluctuating magnetic field induce a weaker current in a strongly diamagnetic metal as compared against a ... | 2,268 |
<p>Consider the following scenario that I actually encounter frequently: I just finished washing a pot in the sink, and now I want to boil some water for cooking noodles. If I fill the pot with hot water from the pipes, my stove will require less energy to bring the water to boiling, but my tankless water heater will... | 2,269 |
<ol>
<li><p>What is the relationship between bound states and scattering length? </p></li>
<li><p>What is the relationship between scattering states and scattering length? </p></li>
<li><p>When we say, potential is 'like' repulsive for positive scattering length and viceversa, are we talking with respect to scattering ... | 2,270 |
<ol>
<li><p>I have some confusion over Vectors, Its components and dimensions. Does the number of vector components mean that a vector is in that many dimensions? For e.g. $A$ vector with 4 components has 4 dimensions?</p></li>
<li><p>Also, how can a Vector have a fourth dimension? How can we graphically represent vect... | 2,271 |
<p>How things radiate electromagnetic radiation? I don't ask why they radiate (higher temperature than 0K) but how they radiate this electromagnetic waves?</p> | 2,272 |
<p>I read that the physical properties of a sound wave correspond to its audible qualities: pitch, volume, and timbre. However, an oscilloscope uses only two-dimensions to accurately depict the physical properties of a wave. Intuitively, pitch and volume seem more basic than timbre does, so I surmise that timbre must c... | 2,273 |
<p>What would the double-slit experiment or something analogous to it look like implemented as a quantum circuit/program? Also, what about the delayed choice quantum eraser, how would that look in a quantum circuit?</p>
<p>For example, if implemented in this quantum computing simulator: <a href="http://www.davyw.com/q... | 2,274 |
<p>When introducing the fine-tuning problem, a sharp cut-off as a regulator in the calculation of the Higgs mass corrections is used. Since this regulator breaks translational and gauge invariance, up to which point can we trust this cut-off as the true validity limit of our theory?</p>
<p>If we do not trust this regu... | 2,275 |
<p>From what (little) I know about physics, I understand that the universe is expanding due to dark energy, and I understand that no one quite understands it yet. I also understand that the cosmic background radiation hints that there were quantum fluctuations in the universe's infancy.</p>
<p>Could the background rad... | 2,276 |
<p>I apologize if this seems like a quack question, but I need some insights by those who know much more than me in Physics.</p>
<p>Anyway, the gravitational "force" (not really a force) is a manifestation of the curvature of space-time, caused due to presence of mass. Suppose I conjecture that ANY force (electroweak,... | 537 |
<p>If you boil water inside a pot the outer rim bubbles first, I imagine because its hotter. Does that same concept apply for the inside of a refrigerator for example. Is the outer rim always more extreme, or at least at first? </p> | 2,277 |
<p>I was wondering what is the difference between the Clausius-Clapeyron equation and the Van't Hoff equation. They appear to have the exact same physical meaning and are often used interchangeably.</p> | 2,278 |
<p>I like to play inside the lift (elevator). For instance, there are bars attached at the side of the lift, and I like to hold my body up using my two hands on the bar. I realised that I actually feel lighter when the lift is decelerating and heavier when it is accelerating. Takes the upward motion as positive. </p>
... | 2,279 |
<p>Wanted to understand the physics behind usage of passive antennae and matched load combination, to absorb, control and reduce the Electromagnetic-Field (s.a. due to microwave radiation from cellular phone towers), within a confined area (s.a. a room). Also, does the shape / size / material used for the antenna have ... | 2,280 |
<blockquote>
<p>Does spontanous symmetry breaking affect the existence of a conserved charge? </p>
</blockquote>
<p>And how does depend on whether we look at a classical or a quantum field theory (e.g. the weak interacting theory)?</p>
<p>(In the quantum case, if we don't want to speak of the Noether theorem, the q... | 2,281 |
<p>Let imagine a tunnel that connect two distant places at the globe (eastern-western or north-south)</p>
<p>There are a lot of posible "distances" or metrics, defined by maps, routes, "as the crow flies", etc.. but none of those distance can be shorter than the distance of the tunel.</p>
<p>So if two trains travels ... | 2,282 |
<p>This may be an elementary question, but if gravity causes a curvature in spacetime, then why isn't everything distorted when looking down on earth, or up at the moon? Shouldn't there be a <a href="http://en.wikipedia.org/wiki/Distortion_%28optics%29#Radial_distortion" rel="nofollow">pincushion effect</a> when viewi... | 2,283 |
<p>I like the lectures by <a href="http://web.mit.edu/physics/people/faculty/lewin_walter.html" rel="nofollow">Walter Lewin</a> 8.0x. However the quality of the videos is pretty bad. Is there any way (DVD, web,...) to get the lecture videos in a good quality, best in HD? </p> | 2,284 |
<p>I see many learned contribution about the role of a <a href="http://en.wikipedia.org/wiki/Theory_of_everything" rel="nofollow">TOE</a>, what it
might do or not do, what kind of answer it might provide, and what
not.</p>
<p>But I do not know what a TOE is, how I would recognize it if I met it
in the street. Is it an... | 2,285 |
<p>Ok so this might be a very stupid and trivial question but I have spent a couple of hours on this little problem.</p>
<p>I am trying to derive a simple formula in a paper. We have a real commuting spinorial variable $y_\alpha$ ($\alpha = 1,2$) ($y^\alpha = \epsilon^{\alpha\beta}y_\beta$, $\epsilon^{\alpha\beta}=-\e... | 2,286 |
<p>I met an approval that massless particle moves with fundamental speed c and this is the consequence of special relativity. Some authors (such as L. Okun) like to prove this approval by the next reasoning.</p>
<blockquote>
<p>Let's have $$ \mathbf p = m\gamma \mathbf v ,\quad E = mc^{2}\gamma \quad \Rightarrow \q... | 2,287 |
<p>I am really stuck on a problem in my textbook:</p>
<p>Water is heated in an open pan where the air pressure is one atmosphere. The water remains a liquid, which expands by a small amount as it is heated. Determine the ratio of the work done by the water to the heat absorbed by the water.</p>
<p>MY ATTEMPT:</p>
... | 2,288 |
<p>I witnessed a phenomenon that I couldn't conclude its cause. Please bear with me for the length of the recall, for I merely want to include any details that might help us to investigate. I had a <strong>cooking glass lid</strong> sat on a wooden shelf that is <strong>away from</strong> the stove and oven and other... | 2,289 |
<p>For my daughter's science experiment, she placed six beverages (cola, diet cola, milk, chocolate milk, apple juice, and water) in the exact same amount in the exact same type and size of plastic cups, and placed all of the cups in a refrigerator at the same time and allowed them to remain in the refrigerator for the... | 2,290 |
<p>Spin-1/2
The eigenspinor , $X=aX_++bX_-$
$$X_+=\left( \begin{array}{cc}
1\\
0\end{array} \right) $$$$X_-=\left( \begin{array}{cc}
0\\
1\end{array} \right)$$
They are define like this because they work well in the following?
$S_zX_+={\hbar}/2X_+$ and $S^2X_+={\frac{3}{4}}{\hbar}X_+$.</p>
<p>But for $|s m \rangle$,... | 2,291 |
<p>I was hoping someone could give an overview as to how the Lie groups $SO(3)$ and $SU(2)$ and their representations can be applied to describe particle physics?</p>
<p>The application of Lie groups and their representations is an enormous field, with vast implications for physics with respect to such things as unifi... | 2,292 |
<p>I want to determine how many minutes a satellite is in a circular orbit around the Earth at about $1000 km$ altitude. I assumed that the Sun-Earth vector lies exactly in the orbital plane of the satellite. Also, in this case, the Sun can be seen as a point light source and the distance to Earth is infinite. Is it po... | 2,293 |
<p>Alright so I really want to put some art into science for my project.project. I'm thinking of creating a beautiful image,preferably in air.I read about the visible lime-green lasers but i still want to be able to use other colors,and I need to make it visible.How can i make "fog" for it so that a pretty image is see... | 2,294 |
<p>The <strong><a href="http://en.wikipedia.org/wiki/amplituhedron" rel="nofollow">Amplituhedron</a></strong> has recently been popular; it supposedly encodes <strong>perturbative scattering amplitudes</strong> in a simple, <strong>geometric</strong> fashion. </p>
<p>What happens to it in a <strong>non-perturbative<... | 2,295 |
<p>Consider a hydraulic jack with massless pistons as follows.</p>
<p><img src="http://i.stack.imgur.com/MVJaU.png" alt="enter image description here"></p>
<p>The famous equation for this system is </p>
<p>$$
\frac{F_1}{A_1}=\frac{F_2}{A_2}
$$</p>
<p>My question is why isn't the equation as follows?</p>
<p>$$
\fra... | 2,296 |
<p>I'm trying to develop some basic intuition here, so this comes mostly as a jumble of commentary/questions. Hope its acceptable.</p>
<p>Helmholtz Free Energy: $A = -{\beta ^{-1}}lnZ$. I find this statement to be incredible profound. Granted, I found it yesterday.</p>
<p>Suppose my system has one energy state wit... | 2,297 |
<p>Given a metric of the form $$ds^2=dr^2+a^2\tanh^2(r/b)d\theta^2$$
why does it follow that $a=b$?
I can't quite spot a constraint condition...</p> | 2,298 |
<p>I'm trying to answer the following question:</p>
<blockquote>
<p>Air consists of molecules Oxygen (Molecular mass = 32$amu$) and Nitrogen (Molecular mass = 28$amu$). Calculate the two mean translational kinetic energies of Oxygen and Nitrogen at 20($^\circ C$)</p>
</blockquote>
<p>To solve it I have done:</p>
<... | 2,299 |
<p>Can someone explain me the meaning of the A/W unit of the photosensivity when reading a spectral response function of the wavelength characteristic of a photodiode?</p> | 2,300 |
<blockquote>
<p><em>A trolley of mass 300kg carrying a sand bag of 25kg is moving uniformly with speed of 27km/h on a frictionless track. After a while, sand starts leaking out of a hole on the floor of the trolley at the rate of 0.05 kg/s.</em></p>
<p><em>What is the speed of the trolley after the entire sand b... | 2,301 |
<p><img src="http://i.stack.imgur.com/1YRyD.png" alt="enter image description here"></p>
<p>The overtones of a vibrating string. </p>
<p>These are eigenfunctions of an associated Sturm–Liouville problem.
The eigenvalues 1,1/2,1/3,… form the (musical) <a href="http://en.wikipedia.org/wiki/Vibrating_string" rel="nofol... | 2,302 |
<p>I'm reading electrodynamics notes and come across that:</p>
<p>$$\int_\text{all space} d\vec r \; \nabla \cdot(\vec A \times \vec B)=0$$ in case of magnetostatics and:
$$\int_\text{all space} d\vec r \; \nabla \cdot(\phi \vec E)=0$$ in case of electrostatics.</p>
<p>($A$ is the magnetostatic potential, $B$ th... | 2,303 |
<p>Let's have Fock state for fermions:
$$
| \mathbf p_{1} , \mathbf p_{2}\rangle = \frac{1}{\sqrt{2}}\hat {a}^{+}(\mathbf p_{1})\hat {a}^{+}(\mathbf p_{2})| \rangle , \quad | \mathbf p_{2} , \mathbf p_{1}\rangle = -| \mathbf p_{1} , \mathbf p_{2}\rangle .
$$
How to get the expression for Slater determinant by starting ... | 2,304 |
<p>Why do we get information about position and momentum when we go to different representations. Why is momentum, which was related to time derivative of position in classical physics, now in QM just a different representation brought about by some unitary transformation. Is Ehrenfest's theorem the only link?</p>
<p>... | 2,305 |
<p>A mass of point performs an effectively 1-dimensional motion in the radial coordinate. If we use the conservation of angular momentum, the centrifugal potential should be added to the original one. </p>
<p>The equation of motion can be obtained also from the Lagrangian. if we substitute, however, the conserved angu... | 2,306 |
<p>I am a reading a book for beginners of the quantum mechanics. In one section, the author shows the <a href="http://en.wikipedia.org/wiki/Inner_product_space" rel="nofollow">inner product</a> of two wave functions $\langle\alpha\vert\beta\rangle$. I am wondering what's the significance of that product? I Googled that... | 2,307 |
<p>QCD is the best-known example of theories with negtive beta function, i.e., coupling constant decreases when increasing energy scale. I have two questions about it:</p>
<p>(1) Are there other theories with this property? (non-Abelian gauge theory, principal chiral field, non-linear sigma model, Kondo effect, and ??... | 2,308 |
<p>I was testing in my lab with water and found that it starts to solidify when it is stationery at 0 degree centigrade.but when I move the liquid with some velocity it dosent change its phase.my interpretation of this happening because when I move liquid it has kinetic energy which dosent allow it to crystallize.but a... | 2,309 |
<p>I spent a while working with MgF2-windowed xenon flash / discharge lamps. Primarily, I characterized their spectra with two normal-incidence spectrometers against a calibrated Deuterium lamp. In this particular case, it included a Czerny-Turner-type design. </p>
<p>As side investigation, I rotated one of the xenon ... | 2,310 |
<p>This is probably trivially related to the question:
<a href="http://physics.stackexchange.com/questions/45922/action-for-a-point-particle-in-a-curved-spacetime">Action for a point particle in a curved spacetime</a> , but am a bit unsure how to write it as a Lagrangian density.</p>
<p>In curved spacetime the action... | 2,311 |
<p>From what I have learned in my chemistry course, Electrons with similar quantum numbers but with opposite spin are attracted to each other. What does this mean when there is a covalent bond being formed between lets say hydrogen and fluorine?</p>
<p>I can think of four different results:</p>
<p>A) A bond is not fo... | 2,312 |
<p>Assuming the solid is less dense than the liquid, will a solid object float on a frictionless liquid?</p>
<p>I can imagine that due to the pressure gradient the object will float, but I can also imagine that without friction there would be no upwards force on the object and it would sink.</p>
<p>What would happen?... | 2,313 |
<p>Are observations of Hawking radiation at the acoustic event horizon in Bose-Einstein condensates consistent with Gravastars?</p>
<p>To reconcile the second law of thermodynamics with the existence of a black hole event horizon, black-holes are necessarily said to contain high entropy while Gravastars not at all. A... | 2,314 |
<p>I know that the main difference between the two is that a battery can provide a constant voltage whereas a capacitor's voltage decreases as the charge stored decreases.
But what about the internal structure ?
A battery also has chemical reactions going inside of it while a <strong>polarized</strong> capacitor also... | 2,315 |
<p>Here is a quote from <a href="http://en.m.wikipedia.org/wiki/Hilbert_space#Hilbert_dimension" rel="nofollow">http://en.m.wikipedia.org/wiki/Hilbert_space#Hilbert_dimension</a> (accessed: Nov. 22, 2013) : </p>
<blockquote>
<p><em>As a consequence of Zorn's lemma, every Hilbert space admits an orthonormal basis; fu... | 42 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/22120/is-the-universe-a-quantum-computer-is-light-speed-barrier-a-computational-cons">Is the universe a quantum computer - is light speed barrier a computational constraint</a> </p>
</blockquote>
<p>Cros... | 43 |
<p>The answer to <a href="http://physics.stackexchange.com/q/6457/2359">a previous question</a> suggests that a moving, permanently magnetized material has an effective electric polarization $\vec{v}\times\vec{M}$. This is easy to check in the case of straight-line motion, using a Lorentz boost.</p>
<p>I suspect this ... | 2,316 |
<p>In general relativity, we use the term "time-like" to state that two events can influence one another. In fact, in order for an event to physically interact with another one, they have to be inifnitely close both in time and space.</p>
<p>As far as I know (correct me if I'm wrong) this principal of "near action/cau... | 2,317 |
<p>If you compress a large mass, on the order of a star or the Earth, into a very small space, you get a black hole. Even for very large masses, it is possible in principle for it to occupy a very small size, like that of a golf ball.</p>
<p>I started to think, how would matter react around this golf ball sized Earth?... | 2,318 |
<p><img src="http://i.stack.imgur.com/5bscW.jpg" alt="enter image description here"></p>
<p>Like the order behavior shown in the image, is it due to the universality of some fundamental mathematic theory? Is there some general physics explanation for it? </p>
<p>-
edit: This question comes after I read Terence Tao's ... | 2,319 |
<p>As far as I know, there is a smooth transition between quantum and classical regimes, so that even classical particle like a massive object has a wavefunction associated with it. However, the double slit experiment can either show quantum character, where the particle supposedly passes through both slits and interfe... | 2,320 |
<p>A neutron outside the nucleus lives for about 15 minutes and decays mainly through weak decays (beta decay). Many other weakly decaying particles decay with lifetimes between $10^{-10}$ and $10^{-12}$ seconds, which is consistent with $\alpha_W \simeq 10^{-6}$.</p>
<p>Why does the neutron lives so much longer than ... | 2,321 |
<p><img src="http://i.stack.imgur.com/z8fR1.png" alt="enter image description here"></p>
<p>I'm making a toy for my kids and this problem came up. I have a channel on a slight angle (angle is between ground and length of channel) and I'm pouring water into it. I want to know how quickly I need to pour water in to make... | 2,322 |
<p>At quantum scale, gravity is the weakest force. <a href="http://physics.stackexchange.com/a/31484/2170">Its even negligible in front of weak force, electromagnetic force, strong force.</a></p>
<p>At macroscopic scale, we see gravity everywhere. Its actually ruling the universe. Electromagnetic force is also everywh... | 2,323 |
<p>Of course it is expected. But how to prove it analytically?</p>
<p>Slater determinant is mentioned in almost every quantum mechanics textbook. But it is necessary to warn the undergraduate students that not every fermionic wave function is a Slater determinant. </p>
<p>So is there any model whose ground state can ... | 2,324 |
<p>I'll apologize in advance if this is not an appropriate place for my question. My background is not in physics, and my understanding of quantum mechanics is extremely rudimentary at best, so I hope you'll be forgiving of my newbish question.</p>
<p>Given a system of entangled particles (eg, 2 or more electrons), p... | 2,325 |
<p>I recall faintly from my quantum theory lecture that there was a really neat way to derive Brillouin-Wigner perturbation theory for the special case of two coupled subspaces that involved a geometric series in reverse. </p>
<p>I know that the beginning was to have the Hilbert space split into subspaces 0 and 1 so t... | 2,326 |
<p>Suppose you have as many electrically charged particles as needed (even countably many) and consider the open unit ball centered at some point in space. For every continuous real valued function on the unit ball, is there a configuration of the particles (outside of the ball) that would generate an electric potentia... | 2,327 |
<p>I'm not talking about an ideal wire in a circuit (a wire with infinite conductance).</p>
<p>I'm talking about an ideal wire in the case of the magnetic field of an infinite current carrying wire. What dimensions must an ideal wire have to better approximate an infinite current carrying wire in terms of its magnetic... | 2,328 |
<blockquote>
<p>A troop $5$ meters long starts marching. A soldier at the end of the file steps out and starts marching forward at a higher speed. On reaching the head of the column, he immediately turns around and marches back at the same speed. As soon as he reaches the end of the file, the troop stops marching, an... | 2,329 |
<p>In $1g$ the average adult human walks 4-5 km in an hour. How fast would such a human walk in a low gravity environment such as on the Moon $(0.17g)$ or Titan $(0.14g)$? </p>
<p>Let's ignore the effects of uneven terrain (regolith or ice/snow/sooth); suppose our human walks on hardened pavement.</p> | 2,330 |
<p>Given the situation that $B=-\nabla A$ where B is magnetic field and A is some Scalar Field. How can I calculate the scalar field, A.</p>
<p>We are dealing with current free region, here.</p>
<p>I know we can calculate B for a infinitely long thin wire given $I$. But I am not sure how we can calculate $A$.</p> | 2,331 |
<p>I actually posted this to <a href="http://math.stackexchange.com/questions/657752/question-on-using-leibniz-formula-to-derive-thin-film-equation-from-navier-stoke">math.stackexchange.com</a> a few months ago but never got any answers.</p>
<p>I am trying to work through the derivation in <a href="https://online.unil... | 2,332 |
<blockquote>
<p>Why is effective length of a bar magnet shorter than its geometric
length?
Blockquote</p>
</blockquote>
<p>in a textbook, author wrote that, effective length is equal to 0.85 times geometric length. But didn't mention the mathematics behind it. I don't understand which keyfactor can determine th... | 2,333 |
<p>When working with path integrals of both bosonic and fermionic field variables, I'm a bit unsure of how to do the usual complete the square trick when an interaction between the two is concerned. Say you have a generic partition function like
\begin{equation}Z=\int D\phi D\bar\psi D\psi \,e^{iS[\phi,\bar\psi,\psi]}... | 2,334 |
<p>I was talking my professor about entanglement swapping between light and matter and it is briefly described here:</p>
<p>You start out with a crystal capable of doing parametric down conversion of incoming photons. When they go in, they undergo a physical process which produces two entangled photons that come out. ... | 2,335 |
<p>My understanding of relativity isn't very sophisticated, but it seems to me that relative to a photon moving at the speed of light, we are moving at the speed of light. Is this the case?</p> | 2,336 |
<p>If a photon hits a proton, would it have a color? What color would it be?</p> | 2,337 |
<p>Even at the core of the sun, the temperature of $\sim 10^7$ K only results in $kT\sim1$ keV, which is about a thousand times less than the electrical potential energy of $\sim1$ MeV needed in order to bring two hydrogen nuclei to within the ~1 fm range of the strong nuclear force. Therefore nuclear fusion reactions ... | 2,338 |
<p>Can one understand Newton's law of gravitation using the holographic principle (or does such reasoning just amount to dimensional analysis)?</p>
<p>Following an argument similar to one given by <a href="http://arxiv.org/abs/1001.0785">Erik Verlinde</a>, consider a mass $M$ inside a spherical volume of space of radi... | 2,339 |
<p>Question 1:Most science textbooks have appendixes that have a value for some physical property of some object. This includes diameter of electrons, viscosity of fluids, boiling points, etc. My question is, are the values presented in such appendixes (or other data bases) averages?</p>
<p>Question 2: Also, suppose I... | 2,340 |
<p>I would like to know what are these formulas used for. There is no intro about it in my book at all, and I am reading Heat Transfer book.
<img src="http://i.stack.imgur.com/nHffh.jpg" alt="enter image description here"></p>
<p>If needed Q. can be edited.</p> | 2,341 |
<p>I'm studying statistical mechanics, in particular classical regime for Fermi Dirac and Bose Einstein gases. Time average value for occupation numbers in FDBE statistics:
$$ \langle n_\epsilon\rangle_{FB} = \frac{1}{e^{(\epsilon-\mu)\beta}\pm1} $$
For Boltzmann Statistics:
$$ \langle n_\epsilon \rangle_B = e^{(\mu-\e... | 2,342 |
<p>So at the end of one of my prof's lectures he gives us something to think about:</p>
<blockquote>
<p>Both electric and magnetic dipoles tend to line up with their
respective fields.</p>
<p>Materials made out of electric dipoles cause the electric field that
turns the dipoles to be <strong>reduced</strong... | 2,343 |
<p>If $\{|\psi_{i}\rangle\}$ is an orthonormal basis for a bipartite system, will $E(|\psi_i\rangle) = E(|\psi_j\rangle)$ for all $i, j$, where $E$ is some entanglement measure?</p> | 2,344 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.