New answers tagged

2

The high voltage causes the gas molecules in the tube to get excited or ionised if the electric field is strong enough. When the excited electrons go back to a lower energy state, they emit photons in the process. The energy of the photons (and therefore colour of light that we see) depends on the energy of the state in which the excited molecule relative ...


1

What would occur if an electron at rest was accelerated to the speed of light? Any charged particle can be accelerated its speed increasing as more energy is supplied, but the limit of the speed is the speed of light. At a Lorentz factor ( = particle energy/rest mass = [104.5 GeV/0.511 MeV]) of over 200,000, LEP still holds the particle accelerator ...


1

Electrons can be accelerated to the speed of light (or practically to the speed of light). If you accelerate electrons to merely 5 MeV the velocity of 0.996 c where c is velocity of light, and yes if they are accelerated to that velocity they will emit gamma like radiation. Here I would like to clarify that the term gamma radiation is mostly used for the ...


1

You are confusing the drift velocity of the electrons (which is < 1 mm/sec) with their Fermi velocity (which is $1.57\cdot 10^6 ~\rm{m/s}$ for copper) - source. If any "bunching up" of electrons were to happen, it would very quickly resolve itself. As was pointed out in the comments, the "signal" that travels in an electrical wire is essentially carried ...


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There are two separate issues here (not sure which of the two you mean): The first problem is a severe misconception that is similar to Zeno's paradox of Achilles and the Tortoise: Given a hydrogen atom we have (in principle) an infinite number of shells. However, the gap between the shells gets smaller and smaller. If you would jump from shell to shell, ...


2

Double-Slit Experiment I believe you are describing the double slit experiment with electrons (as opposed to with light). The pattern you are describing is called an interference pattern (much like two pebbles producing ripples in a pond and there are parts where the ripples cancel out). Below is a diagram of the double slit experiment. One way of ...


0

For the original Bohr Model From Wikipedia of the atom, the separation between energy levels gets smaller as the principal number (n) increases. The value of the energy level is proportional to  -1/n$^2$. this gives a series 1, 1/4, 1/9, 1/16.....The gaps decreasing as n increases. If the orbitals were static in their positions and movement, the ...


1

You're hitting on some of the considerations that led Einstein to his 1905 "Elektrodynamik bewegter Körper" paper. In form of the Lorentz force law you state, the force is the electron's velocity relative to your present frame. The magnetic field $B$ is also as measured in your present frame. You are right to be worried that the whole lot might not be ...


0

The field is just assumed to be fixed over a certain region of space. Then, $v$ indicates the velocity of the charged particle moving uniform w.r.t the inertial frame of magnet. Then the force is given by $$\vec{F}=q\vec{v}\times\vec{B}$$ This is valid for a point charge. Now, suppose a person $A$ is moving on a rail cart. He has a magnet in his hand. The ...


0

The reason this interests me is that no mater how fast the magnet is spinning about its axis there is no difference in the strength or direction of the magnetic field at all points in space Exactly. Your claim about the velocity of the electron being relative to the velocity of the magnet is correct. However, a spinning magnet is just that, a spinning ...


0

In general, electronic relaxation of an excited atom is nothing but a quantum mechanical transition from an initial to a final state. Therefore probabilities for different transitions (what you called paths) is determined by the rules of quantum mechanics. The particular "law" that applies here is called Fermi's Golden Rule. In the related Hyperphysics page ...


3

As regards the first question, if you read this article, it might make the difference between waves and particles clearer. Double Slit Experiment Can absolute zero stop the movement of electrons, or solid electrons like those described above? This is an exerpt from Wikipedia Absolute Zero The laws of thermodynamics dictate that absolute zero ...


3

This is a surprisingly complicated question, and I'm not sure there is a universally accepted answer. To see why this is turn off your magnetic field and give the electron enough velocity to keep it in orbit around the Earth. Now in the Earth frame the electron has a centripetal acceleration of $r\omega^2$ and therefore it should be emitting radiation. ...


3

Cathode Rays First, here's a diagram of a cathode ray tube: Cathode rays were named as such because they were emitted from the negative electrode, or cathode, of a high voltage generator. This was done in a vacuum tube. In the diagram, you can see the cathode, from which the rays (really electrons) were emitted. You can also see a tube that went to a ...


1

The dimensions and meaning of the B coefficients are not the same as the A coefficient. The probability of spontaneous emission does not depend on the radiation environment of the atom, whereas absorption and stimulated emission do. Given that, one has a choice of how one encodes that in terms of the B coefficients, which are only a property of the atom ...


0

I have annotated the diagram in the Wikipedia article that you cited in your question. Note that the signs for the charges on the parallel plates were the wrong way round in the article. To simplify the derivation I assume that the condenser plate length is approximately the same as the source to aperture distance ($AS = a)$ and the angular deflections ...


0

I could be wrong, but there is a phenomenon in physics called quantum superposition. To briefly explain it, an electron can be in all possible allowed places at once until it interacts with another particle causing, in laymen's terms, the universe to "observe" it. When a circuit is closed, the free electrons are given a specific path in which they may go, ...


5

First of all, you can't expect to recover general classical mechanics by simply making averages in quantum mechanics. Apart from very special cases, you can recover it only in the limit $\hslash\to 0$. In such limit, something similar of what you expect can be proved. In particular, it holds when considering (squeezed) coherent states $C_{\hslash}(q,\xi)$ ...


1

The Strong Interaction is responsible for holding together the quark and anti-quark configurations that make up nucleons (aka protons and neutrons). This is due to the necesity to hold together potentially repulsive configurations of these quarks and anti-quarks. As soon as we move past a certain distance away from a nucleon (I forgot what the distance was, ...


7

The strong interaction that keeps protons together is a different kind of force (the strong nuclear force) which does not affect electrons. Electrons don't feel the strong force. They only feel the electromagnetic force and the left-handed ones also feel the weak nuclear force, which converts electrons into neutrinos. As a result, even if two electrons ...


2

Strong interaction refers to a different sense of charge instead of electrostatic charge. At least that is to talk about the most direct use of that interaction. There are much, much weaker corrections that have that as an intermediate interaction (virtual quarks). The joining is Cooper Pairs in superconductors. Look that up to see how it is mediated.


2

Would it be like in gas p/T dependence ? No, it is much more complicated than this. How does the refractive index of plasma changes with temperature? This is an extremely complicated question for numerous nuanced reasons, including (in no particular order): Plasmas are often in a collisionless or weakly collisional state, meaning their dynamics are ...


1

This is almost a duplicate then of Pauli exclusion principle in an electron beam. Almost because it asks about cathode ray beams. The answer there is yes; the Pauli exclusion principle plays a role similar to the neutron star role. For an accelerator beam, where the electrons and positrons are considered free particles, as were the LEP e+ e- beams, the ...


0

Yes, you can make an electron beam. And the Pauli exclusion principle doesn't prohibit it. According to the Pauli exclusion principle, two identical fermions (particles with half-integer spin) cannot occupy the same quantum state simultaneously. Here you may have missed the word simultaneously. An electron can have the same position in space (all quantum ...


3

Several questions of this nature were asked the last days. An electron does not orbit the nucleus as a particle. In Quantum Mechanics the electron is represented by a wavefunction, which gives you the probability of measuring something about the electron. This probability is spherically symmetrical in the ground state of hydrogen, for example: it means you ...


1

$$g(E)=\text{number of states at energy E available to be occupied}$$ $$f(E)=\text{probability that a state with energy E is occupied}$$ so that $$g(E) \ f(E) = \text{average number of occupied states with energy E} \\ =\text{average number of particles with energy E} = N(E)$$ So that the total number of particles will be given by $$N=\int N(E) \ d E$$ ...


3

In a comment elsewhere you write that you're interested in understanding how quantum-mechanical theory describes the radiation that a hydrogen atom does and does not emit. In your question you ask about another answer that suggests some significance to the electron having zero total momentum; I think that's a feature of the coordinate system choice rather ...


-2

The answers posted so far repeat the common fallacy that Maxwell's Equations do not apply to the hydrogen atom. They may not work for the Bohr atom, but they certainly explain everything the hydrogen atom does in terms of its emission and absorption of radiation. In the Schroedinger equation there is a charge density, and for the eigenfunctions of the ...


15

The existence of hydrogen atoms is enough to demonstrate that the electrons don't emit radiation. If they did, that energy would have to come from somewhere. The only place it could come from would be a reduction of orbital radius until the electron finally reaches the nucleus. If you accept that electrodynamics applies, then you have to accept that atoms ...


4

In addition to the answers already given, which answer the question pretty-well, I'll say that, historically, this exact question was the one which puzzled Niels Bohr enough to inspire him to advance his famous theoretical-explanation for the several observed frequencies of the radiations emitted from hydrogen-atoms ... in general, the fact that electrons in ...


9

Because of its wave nature, the electron in its ground state is actually smeared symmetrically about the proton (ignoring spin-spin effects), and spherically symmetric charge distributions do not radiate (there's no special direction). Accelerated charges do not always radiate em radiation. See also How to find the magnetic field due to a revolving electron ...


29

You have your "prove" in the wrong place. The way to prove that ground-state electrons in hydrogen atoms don't emit radiation is the following: Construct a sample of ground-state neutral hydrogen atoms. Place this sample near a detector which is sensitive to the sort of EM radiation you expect. Die of old age waiting for a signal, because ground-state ...


8

I believe some of the answer in the links are correct, others are less obvious and might even be confusing. I am not gonna repeat the arguments there, but to stress the following idea. You cannot demonstrate that using classical electrodynamics. The theory as is does not apply to quantum objects and thus it was modified. The equations are the same, they are ...


2

Please explain by what means electrons extraction can be done. Hot enough plasmas have all the electrons in the plasma leaving the nuclei positive. How person can focus activity on single atom (from precision point of view) to do so? One cannot deal with individual atoms. It is a statistical phenomenon and one can get a beam of ions without any ...



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