# All Questions

134,954 questions
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### Is it possible for a conductor to run out of free electrons?

For example, imagine I apply a high voltage to a piece of conductor (copper) and make the electrons jump out of it like a automotive spark plug. Can the copper after a prolonged period of time run out ...
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Planck's constant $\hbar$ appears in the Schrodinger equation: $$i\hbar \frac{d|\psi\rangle}{dt}\ = \hat{H}|\psi\rangle$$ which implies for stationary states, $$|\psi(x,t)\rangle=e^{-iE_n/\hbar}|\... 0answers 5 views ### Two uniform solid cylinders a and b Two uniform solid cylinders a and b each of mass 1 kg connect by light spring of force constant 200 n/m at their axles and are placed on a fixed wedge as shown in figure.the coefficient of friction ... 0answers 11 views ### Gauge transformation We consider a particle with charge q, the Hamiltonian H, potential function V(x,t) and the vector potential \vec { A } ( x , t ) . The evolution of the wave function \Psi ( \vec { r } , t ) is ... 2answers 113 views ### Why is it necessary to keep UTC within 0.9 seconds from UT1? Why is it necessary to keep UTC within 0.9 seconds from UT1? I thought that UTC in fact more accurate than UT1, so why should it be based on UT1 within that range? Another question would be, why isn'... 1answer 20 views ### Does the Uehling potential have any observable effect? Uehling potential is the correction made to the coulomb potential due to vacuum polarization (electron-positron pair creation and annihilation). How big is this correction compared to the coulomb ... 1answer 115 views ### Is a two-point correlation function of two different fields equal to the multiplication of two one-point correlation functions? \phi_i is a scalar field with a SO(N) invariant N-fields Lagrangian with \phi^4 interactions. After some calculations I arrived to this result: For a\neqb: <T \phi_a(x) \phi_b(y) > = <... 2answers 53 views ### Violation of Stefan's law when shining a light on a black body Suppose there is a black body in a dark room and the room temperature is constant. Now a ray a light is shone upon it. Since a black body absorbs all radiation that falls upon it, it must absorb more ... 0answers 16 views ### Is Einstein's Grandfather's theory is wrong? I claim that Einstein's Grandfather paradox theory is wrong. I find that Einstein told that if one goes to his past and kills his/her grandfather then where his/her existence is? Einstein claims from ... 0answers 8 views ### Mathematics of quantum mechanics for beam splitter I'm reading a book where quantum interference is explained with a common experiment, where photons are thrown to some apparatus formed by two beam splitters: Describing the problem using linear ... 0answers 20 views ### Can neutronic emissions be used as a power source? The free neutron will degrade to a proton electron and anti neutrino in about 15 minutes. Assuming you could slow a beam of free neutrons sufficiently to keep the size of the reactor manageable: Is ... 1answer 20 views ### Gravitation and escape speed I applied conservation of energy at the surface and at the centre of earth which brought me too equation ''- GMm/R =1/2 m v^2 '' having asked my sir he said that gravitational potential energy at the ... 0answers 31 views ### Symmetry acting on a complex fermion operator Suppose S is a \mathbb{Z}_2 symmetry operator, i.e. S^2=1, acting on the fermion c_{n} via$$S c_{n} S^{-1} = \sum_{m} U_{nm} c_{m}$$and I am interested in S is both linear or anti linear, ... 0answers 19 views ### Diffraction due to thin wire [on hold] Here's what I did: The wire ends can be taken as two slits So$$θ=λ/d 2θ=λ/d $$So we have$$s=r2θ $$The relationship between x and s is$$(x/s)=sin(2θ/2) $$r, θ and (a+b) are a part of the ... 0answers 9 views ### Alternative paradigm for the universe indistinguishable from current paradigm ? Why so? How can a universe with fixed size and a speed of light inversely proportional to time since creation be differentiated from the current expanding universe paradigm? The speed being infinite a T=0 is ... 1answer 10 views ### Infinitesimal parameter of Wess Zumino transformation I'm working through the SUSY lecture notes by Lambert, and he does something which seems strange to me during the calculation of the Wess Zumino model. He says the spinor \psi has the ... 1answer 42k views ### Why is black the best emitter? Why are emitters colored black better emitters than other colors? Why is white a worse emitter? 0answers 13 views ### How can an electric field between two parallel plates be constant How can electric field in general and more specifically between two parallel plates be constant, if E depends on distance, how can the electric field be constant. The equation deltaV=Ed, should E not ... 0answers 11 views ### Complex conjugated representation and its Young tableaux This post is an exact copy of one that I posted in Math's site. I do this copy because people there suggested me to do it since, apparentely, in Mathematics and Physics we use defferent conventions ... 0answers 19 views ### Trouble in forming force balance equation for a submerged cylinder [on hold] The question states that, when the liquid level is at a height of h₁ above the wooden cylinder, the cylinder is about to start moving up. What is the value of h₁ in terms of h? My attempt at this ... 0answers 16 views ### Speed of the weight? [on hold] a) If the 20-kg cylinder is released from rest at h = 0, determine the required stiffness k of each spring so that its motion is arrested or stops when h = 0.5 m. Each spring has an unstretched length ... 2answers 57 views ### Inverse of metric tensor The Minkowski metric tensor have the relation \eta_{ij} \eta^{jk}=\delta_i {^k}. That is the inverse of the Minkowski matrix is the matrix itself. Analogously, is it true that g_{ij} ... 1answer 30 views ### Gamma spectrometry Suppose I have a sample containing only 137Cs. Now assume it shows 1000 cps counts for 137Cs, 662keV energy. Now I added 60Co (1173, 1332 keV) source in the same sample. Compton scattering ... 0answers 12 views ### What is BVI Photometry and how is it used? I searched for data about Cepheids light curves (often used as standard candles for measuring distances), and found that all of the data comes in a form of "BVI Photometry" or "BVI Photoelectric ... 0answers 35 views ### What is a singular continuous spectrum? I read some answers about this and the wikipedia page that basically always say that a spectrum can be decomposed into:$$\mu = \mu_{ac} + \mu_{sc} + \mu_{pp}, $$where \mu_{ac} is absolutely ... 1answer 69 views ### Matrix representation of spin-2 system? [on hold] I am surprised no one has asked this before, but what is the matrix representation of a spin-2 system? Also, what are the equivalent of the Pauli matrices for the system? 1answer 10 views ### Newton's rings. Interference by division of amplitude We all know that in wedge shaped film fringes are equally spaced.Being a wedge shaped film Why does the fringe width decrease as order increase in Newton`s ring ? 1answer 14 views ### Confusion of the Isobraic Process Heat equation I was currently reading a wiki article on Isobaric Process (Link at bottom f post). And am confused as to why in there derivation of heat of a an isobaric system they use specific heat capacity for ... 1answer 31 views ### SR time dilation discussion meaningless when there is gravity? Let us say you have three clocks fixed to the spinning earth at the equator. If you set one of this clocks on a plane going eastwards around the globe it will have measured a lesser amount of time ... 3answers 54 views ### Communication near a black hole One ship is in a stable orbit outside of the event horizon of a very large black hole so that there is significant time dilation. Another ship is in its own orbit around the same black hole, but at a ... 0answers 5 views ### How to proof that invisiable metter is not simply function from (visiable mass, time) pair? How to proof that invisiable metter (Dark Matter, Dark Energy) is not simply function from (visiable metter, universe age) pair in terms of known laws of phisics? 0answers 9 views ### Rotational Motion of a thin disc A thin heavy disc can turn freely, about an axis in its own plane, and this revolves horizontally with a uniform angular velocity \omega about a fixed point on itself. Show that the inclination \... 4answers 108 views ### Why electric field inside a cavity of a non conducting not zero Now consider a charged non conducting sphere of uniform charge density , and it as hole of some radius at the centre, now suppose I apply gauss law as there is no charge inside the cavity: so no ... 1answer 162 views ### The physics of a cornering wheel and its centripetal force Can a rolling wheel create a side force without first rotating on a vertical axis? There is something wrong with the way we describe how a cornering vehicle wheel creates a cornering force. I think ... 3answers 29 views ### Orientation of resistor when connected in a cicuit Consider a cuboid shaped resistor. Now Case1: Connect the resistor along is length to a battery. Case2: Connect the resistor along is breadth to a battery. In the two cases the length and cross-... 1answer 26 views ### If infinitesimal transformations commute why dont the generators of the Lorentz group commute? If infinitesimal transformations commute as proved eg here, why are the commutators for the generators of the Lorentz group nonzero? 0answers 19 views ### Determining the height of water level rise in a combined capillary tube What will happen when we fix another capillary tube upon a capillary tube which has not enough space to its free capillary elevation? 3answers 72 views ### Time dilation in a gravitational field A friend and I were talking about relativity and we had different opinions about this situation: If I choose a frame of reference on the surface of a planet, would time "run" differently between the ... 1answer 33 views ### How fast will air travel to fill a vacuum? Suppose I have a sealed glass cylindrical vessel of radius r and length l that is evacuated. I smash one end. How long will it take for air to (a) reach the end of the cylinder (b) fill the vacuum ... 0answers 24 views ### Levi-Civita identity [on hold] with Einstein summation convention What's my problem? 3answers 102 views ### Does the rotational energy change at different points on a sphere? [closed] I know that the linear velocity of a point on the surface of a sphere increases as it goes towards the equator. Therefore, I believe that the rotational energy increases as the position, on the ... 0answers 18 views ### Photoelectric effect wow The effect of electric potential on the threshold frequency in the Lenard's photoelectric experiment I have been taught that electrons can ejected from the atom by applying strong electric field(... 2answers 29 views ### Understanding the potential difference of a wire I'm trying to understand the fundamentals of potential difference in circuits. My understandings (from textbook and stackExchange): Potential difference is created by a separation of charges. A ... 0answers 7 views ### What are the implications of a warmer earth for hurricanes by 2100? The main magic number is the surface sea water temperature. Above, I think 27 C the warm, moist air provides more energy that the storm uses. This is why the hurricane season is late summer into ... 1answer 198 views ### Using fermion-based analog computers to solve NP-hard problems in polynomial time If the fermion sign problem is an NP-hard problem as it seems to be proved by this work, is it possible to take an NP-hard problem, convert it into an equivalent fermionic state evolution problem, ... 1answer 53 views ### Has the “osmium spheres” gravity example ever been done? Calculating the motion of two dense spheres (in a frictionless vacuum) due to gravitational interaction is a classic physics problem that has come up numerous times. Has any real-world space mission ... 0answers 17 views ### Observing a comet and predicting its trajectory I'm planning to observe a comet of apparent magnitude around 18.5 using an observatory telescope. I plan to figure out the trajectory of the comet - all its orbital elements. Given that I only know ... 2answers 181 views ### Doesn't the fact that elementary particles are not black holes prove they are not point structures? De Schwarzschild radius of a mass m is defined as$$r_s=\frac{2mG}{c^2}(m). So if we insert in this formula the mass of an electron (a point particle, according to mainstream physics), which ...
Given the facts that $(E^2 - B^2)$ and $(E\cdot B)$ are Lorentz invariants of the EM field, and that the energy density $(E^2 + B^2)$ is not invariant, it seems that at each point in an EM field there ...