15
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Accepted
The size of elementary particles
In addition to the good answer by @JEB, a bit more information can be added to help understand the issue. The important feature that demonstrates that a particle is a point particle is Bjorken scaling....
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The size of elementary particles
We measure a particle's size by plastically scattering a point particle off it, e.g., to measure the protons size, we do:
$$ e^- + p \rightarrow e^- + p $$
and look at the cross section versus ...
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How can electrons hop large distances if they are connected to the atom which is stationary in an lattice?
They are not connected to any specific atom. The description of electrons belonging to one particular atom makes sense for isolated atoms, but it doesn't work like that in conducting solids. Even in ...
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Can there be clouds of free electrons in space?
Adding to David_h's answer to account for general relativistic effects: in summary you can't actually even create a black hole with any arbitrarily-large number of electrons, because a black hole ...
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How can electrons hop large distances if they are connected to the atom which is stationary in an lattice?
In metals the valence electrons are delocalised and do not belong to a particular atom. In insulators they are localised on a particular atom.
To be localised an electron will increase its momentum ...
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Can there be clouds of free electrons in space?
I can't answer for general relativistic effects, but I would expect that you would need extraordinary initial densities of electrons for those to come into play.
In the Newtonian limit, the situation ...
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The size of elementary particles
Experimentally a point particle is identified by the way that it scatters other particles. A point particle has a characteristic scattering as shown by Rutherford.
When we measure a departure from the ...
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Is it true a cloud of free electrons emits no radiation?
If you have a bunch of charges in a bag at arbitrary positions then the bag will have an electric dipole moment, a magnetic dipole moment, a quadrupole moment etc. If you now give the charges some ...
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Should electrons as tiny magnets, stick to a permanent magnet if in appropriate conditions?
The electrons do have an intrinsic magnetic moment due to their spin.
In order for the permanent magnet to exert an attractive force on them, there usually needs to be a magnetic field gradient as in ...
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Accepted
Radiative or non-radiative emission
If a material absorbs photon, it's electron on outer valence band absorbs its energy and jumps to the higher energy level, when the band gap is similar to the photon's energy.
Firstly, how material ...
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Can there be clouds of free electrons in space?
An obvious corollary to this question is "how massive would a charged particle have to be for the gravitational attraction to overcome the electrostatic repulsion", which is very easy to ...
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Current operator for Bloch electrons
Satisfying the current conservation equation is an unsatisfactory way to define the current because it does not provide a unique answer: you can add any identically conserved current (the curl of ...
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The size of elementary particles
I would say the physical electron is not a point particle as it has the Coulomb field and vacuum polarization, which I believe are part and parcel of the physical electron. Dehmelt said: "an ...
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Can a Wigner crystal form spontaneously, or it will always need an external confining force field?
No, Wigner crystals have net negative charge and the electrons repel each other - it will fly apart without a confining force, as the Schmidt virial argument shows. So you need to add a confining ...
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Radiative or non-radiative emission
The short answer is that radiative decay will happen whenever the energy excites from one band to the other, as intraband transitions have typically very low energies and can couple dispersively to ...
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Double slit experiment with two sources
From a typical high school physics textbook view your question is interesting ... but using a more modern understanding ... maybe taking a quantum optics course ... a new perspective will yield the ...
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Is it true a cloud of free electrons emits no radiation?
A cloud of electrons will explode, probably in a fireball. So yes, there will be black body radiation.
Plasma's are good black body radiators, as they have a wide continuous range of excitations. The ...
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Is it true a cloud of free electrons emits no radiation?
Blackbody radiation is a thermal emission of idealized properties, with spectrum the same as radiation in thermodynamic equilibrium has. No real body or system radiates exactly that, although they can ...
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Does one electron in superposition repel itself?
There are two issues in your question.
First: do two parts of a superposition interact with each other? The answer is no. I think, implicit in your question, is an idea of the quantum state of an ...
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Electron gun design
The two diagrams describe the same apparatus. Only the voltage difference matters.
From a practical perspective, one wants the outside surfaces of a device to be near the ground potential. Exposed ...
rob♦
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