Newest questions tagged electrons - Physics Stack Exchange most recent 30 from physics.stackexchange.com 2019-08-25T16:32:37Z https://physics.stackexchange.com/feeds/tag?tagnames=electrons&sort=newest http://www.creativecommons.org/licenses/by-sa/3.0/rdf https://physics.stackexchange.com/q/498585 3 What binds electrons to a negatively charged material? Marc Perlade https://physics.stackexchange.com/users/239843 2019-08-25T06:18:24Z 2019-08-25T08:16:10Z <p>This is probably a very stupid question but I couldn't find an answer on google.</p> <p>Consider a neutral material - say, some block of metal. There is exactly as many electrons as protons and the electrons are bound to the nuclei with the electromagnetic force. </p> <p>Now, add some electrons to it. It becomes negatively charged, until something with a lower charge contacts it. </p> <p>The electromagnetic force makes negative charges away from other negative charges.</p> <p>So why doesn't the object directly repel its overload of electrons? What prevents them to escape into the vacuum? Is there another interaction that I don't know which is occuring?</p> https://physics.stackexchange.com/q/498564 0 Why do electrons have rest energy? Sasmit Vaidya https://physics.stackexchange.com/users/239834 2019-08-25T03:13:59Z 2019-08-25T04:15:38Z <p>E=mc² so inserting the value of m and c we get 0.511 MeV for electron but then what does this energy account for coz according to me electrons are not made up of any particles so this doesn't account for potential energy neither KE then what does it account for why do a free electron at rest have this energy</p> https://physics.stackexchange.com/q/498514 0 When current flow though a straight wire does it create a magnetic dipole? NoOne https://physics.stackexchange.com/users/239807 2019-08-24T17:29:27Z 2019-08-24T18:15:14Z <p>When current flow through a wire, this generates a magnetic field around the wire, this field tends to circle around the wire and called electromagnetic field.</p> <p>When current flow though a straight wire does it create a magnetic dipole ?</p> <p>If yes, Where are these dipoles (by drawing) ? I didn't see any site draw the dipoles</p> <p>If no, Why do the spinning of the electrons create a dipole but the flowing of the electrons don't ?</p> https://physics.stackexchange.com/q/497916 1 How fast does an electron move? hello moto https://physics.stackexchange.com/users/171360 2019-08-21T00:20:19Z 2019-08-21T05:32:21Z <p>I've been reading this website: www.physics.wayne.edu/~apetrov/PHY2140/Lecture8.pdf to learn how fast an electron moves in a circuit.</p> <p>On page #8, #9 and #10 It says to take the Cross-sectional Area of the wire, The current, The density, The Charge and the electrons^3</p> <pre><code>Area- 3.14x10^-6 ( 2mm thick wire = 3.14 × (0.001 m)^2 = 3.14×10^−6 m^2 = 3.14 mm^2) Current- 10 I Density of copper- 8.95 g/cm^3 charge of 1 electron- 1.6x10^-19 electrons^3- 8.48x10^22 = ( 6.02*10^23 mole * 8.95 g/cm^3 * (63.5 g/mole)^-1 ) Total: 10 / 8.48x10^22 m^3 * 1.6x10^19 * 3.14x10^-6 m^2 = 2.48x10^-6 m/s </code></pre> <p>But they say that with 2.48x10^-6 m/s It'll take the electrons 68 minutes to travel 1 meter, How is that possible?</p> <p>When I calculated that equation I end up with 5.9245283e+35, Then when I try to calculate again to get 68 minutes to travel 1 meter I can never get it right.</p> <p>I'm not the best at math, The m's confused me. What am I missing ?</p> https://physics.stackexchange.com/q/497845 0 What is the physical meaning of a molecular fragment having two appearance energies? Cavenfish https://physics.stackexchange.com/users/238136 2019-08-20T16:19:38Z 2019-08-20T16:19:38Z <p>Appearance energies are particularly import when it comes down to mass spectrometers that use electron impact bombardment. They typically denote the quantum energy value for fragmenting the molecule into two other molecules, for instance the fragmentation sequence <span class="math-container">$CH_4 + e(21.3eV) \rightarrow CH_3 + H^+$</span> is given by <a href="https://webbook.nist.gov/cgi/cbook.cgi?ID=C74828&amp;Units=SI&amp;Mask=20#Ion-Energetics" rel="nofollow noreferrer">NIST Webbook</a>.</p> <p>I understand that these appearance energies are typically found by using a power law fit on data collected at low energy electron bombardment sweeps. The equation used for the fitting typically being,</p> <p><span class="math-container">$$\begin{cases} I = 0 &amp; x &lt; AE\\ I = A(E-AE)^p &amp; x\geq AE \end{cases}$$</span></p> <p>Sometimes researchers use,</p> <p><span class="math-container">$$\begin{cases} I = 0 &amp; x &lt; AE_1\\ I = A(E-AE_1)^p &amp; AE_1 \geq x \leq AE_2 \\ I = A(E-AE_1)^{p_1} + B(E-AE_2)^{p_2}&amp; x &gt;AE_2 \end{cases}$$</span></p> <p>Which results in two appearance energies for the particular fragment investigated. If the appearance energy is quantum mechanical by nature then shouldn't there only be one possible energy value that could produce that fragment. </p> <p>It has been suggested to me that the multiple appearance energies can be attributed to different 'channels' of electron interaction with the molecule(ie: an electron bombardment of Butanol [<span class="math-container">$C_4H_{10}O$</span>] can produce an <span class="math-container">$H^+$</span> by breaking the <span class="math-container">$H-O$</span> bond or <span class="math-container">$H-C$</span> bond). However, if this were the case why are all appearance energies of larger molecules not multi-leveled (ie: <code>n</code> number of AEs where n is the number of ways to fragment the larger molecule into the fragment of interest)?</p> <p>If any of my above understanding is incorrect please tell me, and if possible please explain to me how and why we are able to have two appearance energies for certain fragments.</p> https://physics.stackexchange.com/q/497807 0 Can classic charge radius formula be used to calculate the radius of muons or taus? MichaelPhysica https://physics.stackexchange.com/users/236818 2019-08-20T14:00:36Z 2019-08-20T16:10:56Z <p>The classic charge radius formula <span class="math-container">$r$</span> is used commonly to calculate the radius of electrons(assuming they are spherical). My problem is: can the same formula be used to calculate radii of muons or taus and other leptons and fermions. And if not, what are the radii of muons and taus and how are they calculated? <span class="math-container">$$r=\frac{e^2}{4πε_0mc^2}$$</span> I want to know the radii of muons and taus, and I wonder if the classic charge radius formula given above can be used.</p> https://physics.stackexchange.com/q/497635 0 What differences would be observed in the Stern-Gerlach experiment when using neutral fluorine (Z=9) and neutral sodium (N=11) ECA725 https://physics.stackexchange.com/users/239413 2019-08-19T14:35:36Z 2019-08-19T14:35:36Z <p>I have been working through some past exam papers for my Quantum Mechanics module, and one of the questions is what would be different about observing the results of the Stern-Gerlach experiment when using fluorine (Z=9) and sodium (Z=11)</p> <p>I think that the difference would be something to do with the fact that the unpaired electron in each case is in a different shell, as I have been told to assume that the shells are filled in the order 1s 2s 2p 3s. </p> <p>I was just wondering if someone would be able to really simply explain what the difference would be (if any) and why it occurs. I think I understand the actual experiment and why it was evidence for spin and everything, I just don't know what point I'm missing here (though I'm sure it's very simple!) I'll include the actual question from the exam paper below</p> <p>Thanks in advance :)</p> <blockquote> <p>Briefly explain how the Stern-Gerlach experiment provides evidence for the electron possessing half-integer spin. A student performs two experiments with a Stern-Gerlach apparatus. In the first experiment, a beam of neutral sodium atoms (Z = 11) is passed through the apparatus. In the second, a beam of neutral fluorine atoms (Z = 9) is passed through the apparatus. Explain what you would expect to observe in each case. (You may assume that electron shells are filled in the order 1s, 2s, 2p, 3s.)</p> </blockquote> https://physics.stackexchange.com/q/497582 0 Fractional electric charges HolgerFiedler https://physics.stackexchange.com/users/46708 2019-08-19T08:01:20Z 2019-08-25T14:31:52Z <p>Since the <a href="https://en.wikipedia.org/wiki/Oil_drop_experiment" rel="nofollow noreferrer">Oil droplet experiment</a> we are talking about <a href="https://en.wikipedia.org/wiki/Elementary_charge#Quantization" rel="nofollow noreferrer">elementary electric charges</a>:</p> <blockquote> <p>Charge quantization is the principle that the charge of any object is an integer multiple of the elementary charge. Thus, an object's charge can be exactly 0 e, or exactly 1 e, −1 e, 2 e, etc.</p> </blockquote> <p>This applies with the remark that</p> <blockquote> <p>all isolatable particles have charges that are integer multiples of e. (Quarks cannot be isolated: they only exist in collective states like protons that have total charges that are integer multiples of e.)</p> </blockquote> <p>However, later was discovered the <a href="https://en.wikipedia.org/wiki/Fractional_quantum_Hall_effect#Evidence_for_fractionally-charged_quasiparticles" rel="nofollow noreferrer">Fractional quantum Hall effect</a>:</p> <blockquote> <p>In 1995, the fractional charge of Laughlin quasiparticles was measured directly in a quantum antidot electrometer. In 1997, two groups of physicists ... detected such quasiparticles</p> </blockquote> <p>What prevents us - in addition to the long-standing habit - from speculating about a fractional charge of electrons and protons in the atom?</p> <p>Two questions:</p> <ul> <li>The electrons lose energy (in the form of photon emission) when approaching in the direction to the atomic nucleus, which we explain with potential energy. Is it possible to explain the energy loss by the reduction of the electric fields of the interacting proton and electron during their approach. </li> <li>Following this speculation, how about a remaining fractional charge of electrons and protons in atoms? This could shed new light on nuclear forces as well as electrical neutrality between atoms.</li> </ul> https://physics.stackexchange.com/q/497569 0 Interaction between electrons in which the magnetic dipole moments interact more strongly than their electric fields HolgerFiedler https://physics.stackexchange.com/users/46708 2019-08-19T06:03:51Z 2019-08-19T06:18:41Z <p>Asking a question <a href="https://physics.stackexchange.com/questions/494256/has-anyone-tried-to-incorporate-the-electrons-magnetic-dipole-moment-into-the-at]">Has anyone tried to incorporate the electrons magnetic dipole moment into the atomic orbital theory?</a>, I was curious whether anyone has attempted to relate the intrinsic property of the magnetic moment of the electron to the above-mentioned properties of spin.</p> <p>In the extremely detailed answer (thanks to the author, who took the time despite the pointlessness of such a question) it is clarified that</p> <blockquote> <p><strong>The effects are weak</strong>, and they are secondary to all sorts of other interactions that happen in atoms,...</p> <p>Also, in case you're wondering just how weak: <a href="https://doi.org/10.1103/PhysRev.178.70" rel="nofollow noreferrer">this paper</a> calculates the energy shifts coming from electron spin-spin coupling for a range of two-electron systems. The largest is in helium, for which the coupling energy is of the order of <span class="math-container">$\sim 7 \:\mathrm{cm}^{-1}$</span>, or about <span class="math-container">$0.86\:\rm meV$</span>, as compared to typical characteristic energies of <span class="math-container">$\sim 20\:\rm eV$</span>, some five orders of magnitude higher, for that system.</p> </blockquote> <p>Now there is a new question about <a href="https://physics.stackexchange.com/questions/497223/electron-to-electron-interaction">Electron to electron interaction</a>.</p> <blockquote> <p>There is a critical distance</p> <p><span class="math-container">$$d_\text{crit}=\sqrt\frac{3\epsilon_0\mu_0\hbar^2}{2m^2}=\sqrt{\frac{3}{2}}\frac{\hbar c}{m}=\sqrt{\frac{3}{2}}\overline\lambda_C,$$</span></p> <p>where <span class="math-container">$\overline\lambda_C$</span> is the reduced Compton wavelength of the electron, at which the two forces are equal in magnitude.</p> <p>Since the Compton wavelength is a standard measure of where quantum effects start to be important, this classical analysis can't be taken too seriously. But <strong>it indicates that spin-spin interactions are important at short distances</strong>.</p> </blockquote> <p>I wonder how these two points of view can be related.</p> https://physics.stackexchange.com/q/497361 4 Is Einstein's Photoelectric effect a reversible phenomenon? Christyan Condé https://physics.stackexchange.com/users/239320 2019-08-17T18:17:55Z 2019-08-17T18:40:46Z <p>If one emits a light beam in a given frequency (obviously there is a threshold frequency) over a metal plate, even on low energies, some electrons could be ejected and one could been measuring an electrictal current, briefning these results agrees with Einstein's Nobel's Prize. The question is (in a few words), if one emits a electrons beam over a surface, with some energy who I don't even know the threshold, could exist a light beam (in any frequency of electricmagnetic spectrum) emitted from that surface (metallic or non)?</p> https://physics.stackexchange.com/q/497325 6 From where do electrons gain kinetic energy through a circuit? Mohammad Alshareef https://physics.stackexchange.com/users/227641 2019-08-17T14:19:20Z 2019-08-17T21:06:40Z <p><strong>Supposing an ideal wire</strong>, How do electrons accelerate and gain kinetic energy?</p> <p>What I understand:</p> <p>When a circuit is opened ,electrons are crowded at the negative term of the battery and have high electric potential energy, when we close the circuit electrons <strong>start accelerating and gaining kinetic energy through the wire</strong>.</p> <p>What confuses me: </p> <p>First there isn't an electric field through the wire (an ideal wire) <span class="math-container">${J} =\sigma {E}$</span> ,so I can't say that electrons gain kinetic energy and accelerate due to the electric field.</p> <p>Second, if electrons lose electric potential energy (converted to kinetic energy) then there must be an electric field, because of the definition of voltage: "<strong>electromotive force, is a quantitative expression of the potential difference in charge between two points in an electrical field</strong>".</p> <p>What did I miss?</p> https://physics.stackexchange.com/q/497223 3 Electron to electron interaction jbradvi9 https://physics.stackexchange.com/users/203865 2019-08-16T18:56:15Z 2019-08-16T21:58:25Z <p>I am interested to know if it would be possible to calculate the magnetic attraction between two electrons at zero space between their magnetic poles against electrostatic repulsion between them in simple words can magnetic force of spin hold together two electrons nevertheless there is a electric repulsion.Thanks.</p> https://physics.stackexchange.com/q/496531 0 Are the electrons' orbitals the same for all atoms? Matrix https://physics.stackexchange.com/users/238963 2019-08-13T04:29:45Z 2019-08-13T12:49:46Z <p>Are the electronic orbitals of an atom always quantified in the same way (i.e. the same energy required to reach the next level), or does each atom have its own values for each level?</p> <p><img src="https://i.stack.imgur.com/9gfmm.jpg" width="450"></p> <p>If the quantification is universal, then the creation of photons (due to the deexcitation of the electrons) at the wavelength / color corresponding to the transition should be more abundant in the universe than all the other frequency. Except one detects no more photon of a given wavelength than of another.</p> <p>So where is my reasoning error?</p> https://physics.stackexchange.com/q/496261 0 Relation Between Current and velocity of electrons VKJ https://physics.stackexchange.com/users/219729 2019-08-11T16:14:07Z 2019-08-11T17:00:08Z <p>In a conductor, all the electrons are few to move to conduction bands.</p> <p>If we say that magnitude Current is increased (I= dq/dt) can we infer that the velocity with which the electrons flow also increases if all the electrons are already involving in conduction?</p> https://physics.stackexchange.com/q/495816 1 Multi electron interference in double slit experiment Sohan Biswas https://physics.stackexchange.com/users/238633 2019-08-08T09:29:33Z 2019-08-08T10:54:46Z <p>Electrons have negative charge, and therefore repel each other. That should mean that their position, and momentum probabilities should get skewed away when in the presence of some other electron. I.e. probabilities of them being close together should be very low.</p> <p>So, if we send in two electrons at a time towards the slits, the probability that they passed through the same slit should be pretty low. Now I have two questions :</p> <p><span class="math-container">$1)$</span> What happens if we detect the electrons at one of the slits? If we see only one electron enter that slit, then the other electron must either have gone through the other slit, or not gone in. Does interference still occur?</p> <p><span class="math-container">$2)$</span> Why do electrons interfere anyway. In the two electron case, they should repel each other, and therefore their interference should greatly decrease, right?</p> https://physics.stackexchange.com/q/495530 0 Photon-Electron interaction (Compton and Photoelectric effect) Srikanth Balakrishna https://physics.stackexchange.com/users/238513 2019-08-06T13:31:54Z 2019-08-06T13:31:54Z <p>(Some context : I am a first year engineering student and i have conceptual doubts in Compton and photoelectric effect. I have read a book "Concepts of modern physics"-Arthur Beiser and talked to my professor in hopes of clearing my doubts. Neither has succeeded in explaining the interaction between a photon and an electron adequately. My question may seem very fundamental or even vague and I'm sorry for that)</p> <p>1)What happens to the electron in Compton effect?</p> <p>Case 1: An X-ray photon hits an electron in the valence shell of the atom.Due to an interaction unknown to me, the photon loses some energy and scatters.In this case the X-ray has a high enough energy that we can treat the valence electron as a free electron. What happens to the electron in this case?Does it excite to a higher energy state or does it stay in its orbit?Does it completely separate from the atom and move around in the bulk of the metal or does it even escape the metal surface?</p> <p>Case 2: A photon from the visible spectrum hits a valence/'loosely bound' electron</p> <p>Case 3:An X-ray photon hits an inner electron(tightly bound to nucleus)</p> <p>Case 4:A photon of the visible spectrum strikes an inner electron.</p> <p>2)In what cases does photoelectric effect occur instead of Compton Scattering?</p> <p>I am confused as to what happens because google searches reveal other types of scattering that I haven't even heard of.I am merely starting out with quantum physics so any lack of clarity in my question is regretted,Please tell me how I can clarify myself and I shall try to do so.</p> <p>3)Another question i have is what happens if the photon's energy does or does not correspond to the energy gap between any two orbits?And what happens if an excess amount of energy is supplied,greater than the ionization energy/work function(whichever is relevant)</p> <p>I know that it is a lot to read and answer,so even the tiniest help is deeply appreciated :)</p> <p>Any references to any books or sources, that explain the physical mechanism that is occurring here,are also welcome</p> https://physics.stackexchange.com/q/495190 1 What is actually being removed when a metal conductor is grounded? Kevin N https://physics.stackexchange.com/users/226894 2019-08-04T14:48:16Z 2019-08-04T18:09:53Z <p><a href="https://i.stack.imgur.com/HBBmt.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HBBmt.jpg" alt="enter image description here"></a></p> <p>I found this image earlier this morning, and yes, there are a lot of diagrams/illustrations about this, transferring charges by induction has been introduced since the very beginning of high school and is very straightforward.</p> <p>But I noticed something odd about these illustrations, it is said that if, in this case, a sphere has excess positively charged particles, the earth would try neutralizing it by sending <em>electrons</em> (negative charges), but in figure <span class="math-container">$(a)$</span> the amount of positive and negative charges are equal (<span class="math-container">$3+$</span> and <span class="math-container">$3-$</span>), so where are these called <em>excess charges</em>, if the metal sphere/conductor is completely neutral?</p> <p>Any response would be very helpful!</p> https://physics.stackexchange.com/q/495112 0 Working out the radial arc of a magnetic field to get mass of electron Recon https://physics.stackexchange.com/users/238344 2019-08-04T01:14:04Z 2019-08-04T03:15:31Z <p>We have an experimental setup as below, the magnetic field strength, Bq/30s, and distances (magnet distance, Geiger counter height, Geiger to magnet centre distance) have all been recorded. The energy of the particle is also known.</p> <p>We are trying to calculate the radius of a charged particle in the motion of the magnetic field, in order to prove the mass of an electron using the equation <span class="math-container">$\ r=mv/qb$</span>.</p> <p>We have tried using both the formulas for kinetic energy and Einsteins <span class="math-container">$\ e=mc^2$</span> in order to solve the mass and radius. </p> <p>Is there any way to calculate the radius or mass of an electron using this setup? And how? Assuming we can't get any more variables.</p> <p>Thanks</p> <p><a href="https://i.stack.imgur.com/4tHoE.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4tHoE.png" alt="experiemnt setup"></a></p> https://physics.stackexchange.com/q/495024 1 Does an electron emit radiation the instant it absorbs it? Chatrapal Singh Rathore https://physics.stackexchange.com/users/238307 2019-08-03T13:14:02Z 2019-08-03T14:07:54Z <p>I was reading on the electromagnetic spectrum when I thought if an atom/electron is absorbing the energy from the light ray falling on it, how and by when will it get rid of the excess energy to become stable again. If it emitted the light radiation at the same instant, wouldn't it interfere with the emission spectrum band?</p> https://physics.stackexchange.com/q/494854 1 From where does the radiation come from in an inverse-Bremsstrahlung process? Élio Pereira https://physics.stackexchange.com/users/75538 2019-08-02T13:45:57Z 2019-08-02T14:18:51Z <p>I'm trying to know more about Bremsstrahlung and inverse-Bremsstrahlung processes. If you know any good references that treat theses topics with a good mathematical and physical basis, please let me know.</p> <p>I understood that in a Bremsstrahlung process a charged particle emits radiation when interacting with another one (for example an electron and a positive ion), since the interaction causes an acceleration, and any accelerated charged particle emits radiation. The radiation would come from the particles, causing a loss of kinetic energy. I also discovered that an absorption of radiation can also occur in such process, being the name of that process an "inverse-Bremsstrahlung". In such case where does the radiation come from? Does it simply come from the background? It seems that too many ingredients need to be in harmony so that such process can happen.</p> https://physics.stackexchange.com/q/494755 1 Why is order of electron orbital filling not completely sequential? [duplicate] Arcane Blackwood https://physics.stackexchange.com/users/238197 2019-08-01T22:24:47Z 2019-08-02T01:49:17Z <div class="question-status question-originals-of-duplicate"> <p>This question already has an answer here:</p> <ul> <li> <a href="/questions/255465/why-do-electrons-not-fully-fill-up-all-the-orbitals-sequentially" dir="ltr">Why do electrons not fully fill up all the orbitals sequentially?</a> <span class="question-originals-answer-count"> 1 answer </span> </li> </ul> </div> <p>Orbitals fill in the following order, 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, etc. Its a nice pattern that many elements follow, but there are exceptions to. For example:</p> <p>V: 1s<sup>2</sup> ... 4s<sup>2</sup> 3d<sup>3</sup><br> Cr: 1s<sup>2</sup> ... 4s<sup>1</sup> 3d<sup>5</sup></p> <p>And not: (which would seem to be breaking pattern)</p> <p>Cr: 1s<sup>2</sup> ... 4s<sup>2</sup> 3d<sup>4</sup></p> <p>This can also be seen on other elements, where a higher shell 'steals' from one below it in a seemingly random order. Is there a reason behind this, and if so, even if complex, what pattern is there to it?</p> <p>I am new to the world of the very small, new to chemistry. Any help is greatly appreciated.</p> https://physics.stackexchange.com/q/494256 -7 Has anyone tried to incorporate the electrons magnetic dipole moment into the atomic orbital theory? HolgerFiedler https://physics.stackexchange.com/users/46708 2019-07-29T19:53:25Z 2019-07-31T01:10:58Z <p>The Pauli exclusion principle is related to the electrons spin. The quantum numbers are complete only with the spin quantum number. I am curious whether anyone has attempted to relate the intrinsic property of the magnetic moment of the electron to the above-mentioned properties of spin.</p> <p>If there aren’t sources, I have an additional question. How one imagine the orientation of the magnetic dipoles of the electrons in each shell? If one does not deny these dipole moments (and there is no reason for that?) then we would also have to deal with their effects.</p> https://physics.stackexchange.com/q/494070 0 Charge on an electrical conductor Gourav Mahunta https://physics.stackexchange.com/users/236862 2019-07-28T17:30:52Z 2019-07-28T17:45:29Z <p>Consider we have very precise equipment (s) needed for this question. There's a finitely big uncharged conducting sphere. Suppose we had an extra electron from an external source and we plan to keep it on the sphere. Then how would that one electron arrange itself on the sphere? Where would it be placed?</p> <blockquote> <p>I'm aware of the fact that the net electric field inside a conductor is zero. Considering it to be very basic I don't need a proof for that. If there would be 2 or more electron it's very easy to think about how would they align themselves in order to cancel the net electric field at any point inside the conductor. But when there's only one electron it's hard to imagine.</p> </blockquote> https://physics.stackexchange.com/q/494002 1 How do electrons keep moving when bare copper wires are rolled? [closed] molo32 https://physics.stackexchange.com/users/237861 2019-07-28T07:58:28Z 2019-07-28T09:43:51Z <p>How do electrons keep moving when bare copper wires are rolled?</p> <p>When someone strips the wires and coils the copper, does that not affect the communication between the devices, that is, the bits do not arrive corrupt?</p> https://physics.stackexchange.com/q/493664 0 Does electron affinity decrease with charging? Patrick https://physics.stackexchange.com/users/157880 2019-07-26T04:18:25Z 2019-07-26T04:18:25Z <p>Lets consider two materials A having higher electron affinity than B while both are not too far off. If they are both insulators and A accumulate charges due to triboelectric effect. Than after a certain point of accumulating, does the electron affinity of A decrease? would it ever be possible for some A materials to be overcharged so that it give electrons to B(that has previously lost many electrons to other A particles) despite their innate electron affinity? Thanks</p> https://physics.stackexchange.com/q/493490 1 What is the exact mechanism of flow of electricity? Tushar https://physics.stackexchange.com/users/223406 2019-07-25T08:43:24Z 2019-07-25T09:57:26Z <p>When a steady current flows through a conductor, the electrons in it move with a certain average ‘drift speed’. One can calculate this drift speed of electrons for a typical copper wire carrying a small current, and it is found to be actually very small, of the order of 1 mm s-1. How is it then that an electric bulb lights up as soon as we turn the switch on? It cannot be that a current starts only when an electron from one terminal of the electric supply physically reaches the other terminal through the bulb, because the physical drift of electrons in the conducting wires is a very slow process. </p> <p><strong>What is the exact mechanism of the current flow, which takes place with a speed close to the speed of light ?</strong></p> https://physics.stackexchange.com/q/493185 1 Why doesn’t the focussing anode diverge the electron beam again? Atom https://physics.stackexchange.com/users/231957 2019-07-23T14:39:18Z 2019-07-23T14:39:18Z <p>Consider this diagram of a focusing anode in a CRT: <a href="https://i.stack.imgur.com/REXFj.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/REXFj.jpg" alt="enter image description here"></a></p> <p><strong>Question:</strong> Why does the electron beam not diverge again when it enters the focussing anode (or accelerating anode) while leaving the pre-accelerating anode (or focussing anode)?</p> <p>I think the answer is that it <em>does</em> diverge but <em>less</em> than it converges at both entrances. And since it converges <em>first</em>, the resultant is relatively convergent. The following is how I show it: <a href="https://i.stack.imgur.com/zzVeG.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zzVeG.jpg" alt="enter image description here"></a></p> <p>Is it correct?</p> https://physics.stackexchange.com/q/493137 0 Why are 2 gamma photons created? [duplicate] John Hon https://physics.stackexchange.com/users/115337 2019-07-23T08:40:55Z 2019-07-23T09:13:11Z <div class="question-status question-originals-of-duplicate"> <p>This question already has an answer here:</p> <ul> <li> <a href="/questions/216886/positron-electron-annihilation-can-more-than-two-photons-be-created" dir="ltr">Positron-electron annihilation - can more than two photons be created?</a> <span class="question-originals-answer-count"> 2 answers </span> </li> </ul> </div> <p>When a positron and an electron come together they annihilate and produce 2 gamma photons <span class="math-container">$$e^+ +e^- \rightarrow 2\gamma$$</span></p> <p>I can understand that they must be produced in pairs to conserve momentum. However, that still leaves all other even numbers. Why 2 photons, why not 4,6, 8, 10... photons?</p> <p>Note it is NOT a duplicate of <a href="https://physics.stackexchange.com/questions/301658/why-are-two-photons-created-in-annihilation">Why are two photons created in annihilation?</a> because that question only asks how can mass-less particles have momentum.</p> https://physics.stackexchange.com/q/493053 0 Analogy What is the difference between AC light and DC light or is there such a thing? [closed] jmazaredo https://physics.stackexchange.com/users/237454 2019-07-22T19:19:37Z 2019-07-27T07:15:53Z <p>Is there a constant non changing static light? See analogy</p> <p>Analogy As AC is for alternating current DC is for direct current</p> <p>AC for sine Waves/Movement/Varies to light DC for + or - straight line/not moving/non changing/ non flickering</p> <p>Update : Additional info on my question if my thinking is right (maybe or maybe not)</p> <p>We can see light because it varies pulse or something like that? Can I say like pulsating/alternating like an AC?The question is, is there a constant like DC straight not changing?</p> <p><strong>The question is analogy</strong></p> https://physics.stackexchange.com/q/492986 1 Are Cooper pairs (of electrons) entangled? Árpád Szendrei https://physics.stackexchange.com/users/132371 2019-07-22T12:05:32Z 2019-07-22T12:05:32Z <p>I have read this question:</p> <p><a href="https://physics.stackexchange.com/questions/136070/does-a-normal-torch-emit-entangled-photons/252948#252948">Does a normal torch emit entangled photons?</a></p> <p>where Quantum Journalist says:</p> <blockquote> <blockquote> <p>Although all the particles of a BEC are in a single quantum state, they are not entangled, but rather the macroscopic wavefunction can be separated as a product state</p> </blockquote> </blockquote> <p><a href="https://physics.stackexchange.com/questions/449757/can-superconductivity-be-understood-to-be-a-result-of-quantum-entanglement">Can superconductivity be understood to be a result of quantum entanglement?</a></p> <p>where Chiral Anomaly says:</p> <blockquote> <blockquote> <p>The BCS state describing a conventional superconductor is indeed an entangled state, involving a superposition of different numbers of Cooper pairs, each of which involves a superposition of different combinations of paired momenta. An important thing about the BCS state is the specific way in which the electrons are entangled with each other. BCS superconductivity relies on the fact that many Cooper pairs can occupy the same "state," using the word "state" here like the word "orbital" in atomic physics. The particular way in which the electrons are entangled with each other is what makes this possible despite the fact that electrons <em>individually</em> obey the Pauli exclusion principle. But now consider the operator <span class="math-container">$$B \equiv \sum_{k,s} B(k,s)c^\dagger(k,s)c^\dagger(-k,-s),$$</span> which is a rough analogue of the operator that creates a Cooper pair. The momenta and spins of the two electrons in this pair are entangled with each other (because the sum cannot be factorized). As a result of this entanglement, we have <span class="math-container">$$B^n|0\rangle\neq 0$$</span> even for large <span class="math-container">$n\gg 1$</span>. The individual electrons still obey the Pauli exclusion principle (the operators <span class="math-container">$c^\dagger$</span> still anticommute with each other), but their entanglement means that plenty of terms in the product still survive even after taking this anticommutativity into account, leaving a nonzero result.</p> </blockquote> </blockquote> <p>Now in a BEC, a large number of bosons occupy the same quantum state, at which point microscopic phenomena, like wavefunction interference becomes appearant macroscopically.</p> <p>Now cooper pairs of electrons, attracted, can have a lower energy level then the Fermi level.</p> <blockquote> <blockquote> <p>Electrons have spin-​1⁄2, so they are fermions, but the total spin of a Cooper pair is integer (0 or 1) so it is a composite boson.</p> </blockquote> </blockquote> <p>This means, that if we know the spin of one of the electrons from the Cooper pair, then we have information about the spin of the other electron in the Cooper pair.</p> <blockquote> <blockquote> <p>Quantum entanglement is a physical phenomenon that occurs when pairs or groups of particles are generated, interact, or share spatial proximity in ways such that the quantum state of each particle cannot be described independently of the state of the others, even when the particles are separated by a large distance.</p> </blockquote> </blockquote> <p>So basically Cooper pair of electrons should be entangled, because information of the spin of one of the electrons will give us info about the spin of the other electron in the pair. </p> <p>BEC says that the wavefunctions can interfere, but it does not say they are entangled.</p> <p>Question:</p> <ol> <li>Are Cooper pairs of electrons entangled?</li> </ol>