Hot answers tagged electron
29
One good piece of evidence that all particles of a given type are identical is the exchange interaction. The exchange symmetry (that one can exchange any two electrons and leave the Hamiltonian unchanged) results in the Pauli exclusion principle for fermions. It also is responsible for all sorts of particle statistics effects (particles following the ...
18
First of all -- it wouldn't be called "the Large Hadron Collider", right?
Looks like one would rather call it something like "Large Electron-Positron Collider".
In that case one definitely would need another abbreviation for it. Something like "LEP" instead of "LHC"...
Now, guess what was there in the same tunnel before?
Edit: since my shenanigan got ...
17
The state of an electron (or electrons) in the atoms isn't an eigenstate of the velocity (or speed) operator, so the speed isn't sharply determined. However, it's very interesting to make an order-of-magnitude estimate of the speed of electrons in the Hydrogen atom (and it's similar for other atoms).
The speed $v$ satisfies
$$ \frac{mv^2}2\sim ...
14
A neutron is not a proton and an electron lumped together (as your question seems to suggest you think)
A hydrogen atom is a bound state of an electron and a proton (bound by the electromagnetic force) whereas a neutron is a bound state of three quarks (bound by the strong force).
You might be tempted to think that a neutron is also a bound state of an ...
14
Let me start by saying nothing is known about any possible substructure of the electron. There have been many experiments done to try to determine this, and so far all results are consistent with the electron being a point particle. The best reference I can find is this 1988 paper by Hans Dehmelt (which I unfortunately can't access right now) which sets an ...
13
This is an example of what is sometimes called the "Marquee Effect." Think of the light bulbs surrounding an old-fashioned movie theater marquee, where the light bulbs turn on in sequence to produce the illusion, from a distance, of a light source which is moving around the the marquee.
There is no limit on how short the time interval is between one light ...
12
There are two points in answering this question:
Design: The design of the collider would have to be different. Electrons/positrons in a cyclotron radiate synchrotron radiation when they are accelerated (which itself is a useful device). To get above a few GeV, researchers use linear accelerators, such as SLAC. The proposed International Linear Collider is ...
10
Interesting, but I'm don't think you are asking the right questions in the context of law.
The point is that electrons and electricity are completely irrelevant when it comes to the question of "tangible" and "electronic" "goods". You will obtain a good answer only if you forget about electricity, which just happens to be a convenient physical carrier of ...
9
This is a conflation of phase velocity, and group velocity.
The beam can be seen to move from say left to right at higher than c, but no information or particles are traveling that fast. Information is being transmitted from the electron gun to the phosphor at well under the speed of light.
It has nothing to do with the media it is embedded in. The ...
9
It's not a mistake, and conventional current is not wrong or backwards.
The labeling of one polarity of charge as "positive" and the other as "negative" is totally arbitrary. It could be done either way and everything would still work out the same. Franklin didn't choose wrong; he just chose. Labeling protons as negative and electrons as positive wouldn't ...
9
Electric current, by definition, is a flow of charged particles.
When someone says it is the propagation of the electric field, usually he means the following:
The velocity of the electrons in the wires is very slow (few cm/s if I remember it right), but when one turn on the light he doesn't see any delay. The lamp starts lighting when the electrons start ...
8
No, it is not a proof of that. As Robert Laughlin demonstrated,
http://en.wikipedia.org/wiki/Laughlin_wavefunction
one may explicitly write down a wave function involving electrons, particles with charge $-|e|$, that reproduces all the fractional observations. He got a Nobel prize for this wave function in 1998.
It may be useful to preemptively notice ...
7
It is not a matter of "falling in": all s orbitals have non-trivial probability densities at the center.
It is about energy balance in the nucleus.
Kr-83 is a lower energy configuration than Rb-83 by enough to make up for the neutrino and the gamma(s). Evidently Kr-85 is not a sufficiently lower energy state than Rb-85.
7
I will try to adress the misunderstandings first, then answer the question.
Particle exchange force model is not causal
There is a flaw in your thinking, in that you are formulating the electromagnetic interaction in terms of photon emission and absorption and at the same time telling a story forward in time. These two ideas are both ok separately, but not ...
7
There's an old and clichéd but actually pretty good analogy for understanding electric circuits, and that's to think of the circuit as water plowing through pipes.
If you have a pipe full of water, and you turn on the tap at one end, water immediately starts flowing out of the other end. Well not quite immediately: when you turn on the tap you raise the ...
7
Suppose you had three electrons, with individual wavefunctions $\lvert \psi_1 \rangle$, $\lvert \psi_2 \rangle$, and $\lvert \psi_3 \rangle$. Let them all have the same $\vec{x}$, $l$, and $m$, so they can only differ in intrinsic spin. Since spin is a two-dimensional Hilbert space, as you noted, then three vectors must be linearly dependent. That is, there ...
6
Yes Sam, there definitely is electric field reshaping in the wire. Strangely, it is not talked about in hardly any physics texts, but there are surface charge accumulations along the wire which maintain the electric field in the direction of the wire. (Note: it is a surface charge distribution since any extra charge on a conductor will reside on the ...
6
A neutron is a fermion, a hydrogen atom is a boson. This is related to the fact that a neutron decays into three fermions rather than two which is what you seem to think.
A neutron is composed of three valence quarks, $u,d,d$, while a hydrogen atom is made out of $u,u,d,e^-$.
The internal size of a neutron is about $10^{-14}$ meters while the internal size ...
6
A nice bubble chamber picture:
"Electrons and positrons produced simultaneously from individual gamma rays curl in opposite directions in the magnetic field of a bubble chamber. In the above example the gamma ray has lost some energy to an atomic electron, which leaves the long track, curling left. The gamma rays do not leave tracks in the chamber, as they ...
6
I think that the paper is completely wrong and the conclusions are preposterous. The paper argues that when one models the vicinity of the electron as a rotating black hole, he will get new effects.
However, the black hole corresponding to the electron mass – which is much lighter than the Planck mass – would have a much smaller radius than the Planck ...
6
No, it is not true. A quantum computer stores the same $2^n$ states that the classical computer stores. The difference is that the quantum computer stores a linear superposition of those states, where the classical computer can only store one of those states at a time. What you refer to as '0 & 1' qubits are actually linear superpositions of the two ...
5
The spin of a single electron has been measured since the very first moment when the people understood that every electron possesses a spin. A Stern-Gerlach experiment - a magnetic field - is enough to measure the spin:
http://en.wikipedia.org/wiki/Stern-Gerlach_experiment
5
Electronic goods can be transmitted without exchanging electrons (think of wi-fi networks). They actually don't even need electricity at all, for example vouchers can be sent through normal post.
What changes is the configuration of electrons and electromagnetic fields in the electronic device which contains the goods. This is simply a "state". For example ...
5
What you've written down is the spatial part of the electron wavefunction. The spin state is not included. The full wavefunction of the electron involves both the spatial part and the spin part. Sometimes in quantum mechanics books the full electron wavefunction is written as the tensor product of the spatial and spinor parts, sometimes you'll just see it ...
5
Typical commercial CRTs for televisions or computer monitors have electron guns that work in the range $5-30\text{ keV}$. Such electrons have a very short penetration depth in solids and will essentially all be stopped in the collimator or the glass of the tube.
See the Particle Physics Data Book chapter on the Passage of Particle Through Matter (PDF ...
5
The electron is annihilated by the positron of the pair, and the other electron stays.
The "normal" virtual creation/annihilation process is
$$\text{nothing} \rightarrow e^- + e^+ \rightarrow \text{nothing}$$
If you add an electron nearby which does not interact with the pair, this becomes
$$e^- \rightarrow 2e^- + e^+ \rightarrow e^-$$
and if the ...
5
The first thing to notice, as pointed out in the comments, is that time increases going up. So if you are more familiar with viewing Feynman diagrams where time increases to the right, this problem is easily solved: just rotate the diagram by 90 degrees when you are interpreting it.
If the problem is that you're not all that familiar with matter lines in ...
5
Ne is used,
Because it caused the red glow inside the tube, infact you can get a whole array of colors using different noble gases. eg. Ne => Red, Xe => Whitish Blue, Ar => Blue etc. Check Wikipedia for more.
Because even when it exist as plasma, it doesn't react with the filament inside the tube or the glass walls, this helps in the longer life of lamp, ...
5
The magnetic force is
$$ \vec F = q \vec v \times \vec B $$
so with a constant $\vec B, \vec v$, it's clear that the opposite sign of $q$ leads to the opposite force. So antiparticles surely bend in the opposite direction than the original particles.
Concerning your "right hand rule", I think that whichever you meant, it was misintetrpreted. Right hand ...
5
Dirac's derivation of the existence of positrons that you described was a totally legitimate and solid argument and Dirac rightfully received a Nobel prize for this derivation.
As you correctly say, the same "sea" argument depending on Pauli's exclusion principle isn't really working for bosons. Modern QFT textbooks want to present fermions and bosons in a ...
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