New answers tagged

0

Here's a second answer which addresses the innards of the question, rather than simply the title: Is the total momentum of the electron in a hydrogen atom zero? The ground-state electron wavefunction is, up to a normalization, $$ \left|\psi_{100}\right> = e^{-r/2a} = \exp \frac{-1}{2a}\sqrt{x^2+y^2+z^2} $$ The momentum operator is $\hat p = i\hbar \vec\...


0

The electron could emit radiation only by lowering its energy. But quantum mechanics says that energy is quantized for the bound states of the $1/r$ potential, and only certain values of energy are allowed. The electron would then have to decay to a lower energy level, but since it is already in the lowest possible level (the fundamental state), it cannot go ...


-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 ...


5

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 ...


26

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 ...


0

Neutral is a circuit conductor that normally carries current back to the source, and is connected to ground (earth) at the main electrical panel. In the electrical trade, the conductor of a 2-wire circuit connected to the supply neutral point and earth ground is referred to as the "neutral". A difference can occur when either current is flowing down the ...


2

For wave mechanics there is the phase velocity and group velocity. For the energy $E~=~\hbar\omega$ the phase velocity is $$ v_p~=~\frac{\omega}{k}~=~\frac{\hbar}{2m}(k~+~ck^3). $$ This is the velocity of a wave front, or where the phase of the wave is constant. There is also the group velocity that is $$ v_g~=~\frac{\partial\omega}{\partial k}~=~\frac{\hbar}...


1

$f(E)$ is the probability that a quantum state of energy $E$ is occupied. There are two quantum states (for two spin states) at each energy. The probability cannot be doubled, since that could then exceed 1. All that happens for a spin $1/2$ particle is that the number of available quantum states is doubled.


1

Your confusion arises from the fact that you are confusing scalars and vectors. Scalars, are like numbers, and they have only magnitude. Vectors on the other hand have direction in addition to magnitude. In your question, you mention the wave vector, which, as its name suggests, is a vector. Typically vectors are written in bold or with an arrow over them; ...


0

You have the following identity $$\gamma^{\nu}\gamma^{\mu}\gamma^{\rho}\gamma^{\sigma}\gamma_{\nu}=-2\gamma^{\sigma}\gamma^{\rho}\gamma^{\mu}$$ This gives you that $$\gamma^{\nu}\not{k^{'}}\gamma^{\rho}\not{k}\gamma_{\nu}=-2\not{k}\gamma^{\rho}\not{k^{'}}$$ Which is exactly what you need to get the above expression.


0

Electron around nucleus is described by complex wave function with both real and imaginary parts.The electron is no longer described as moving around the nucleus but is found with a certain probability around the nucleus as given by the Schrodinger's equation. Here probability is a measure of chance of finding an electron over a region. If one can measure (...


2

We don't need to separate electrons out in order to observe them. The structure of an atom, as revealed in electron transitions (atomic spectroscopy) is clearly based on orbitals at specific energy levels, with a two-electrons-per-orbital limit. And, the collective behavior of unpaired electrons that gives rise to ferromagnetism, and subtle spectroscopic ...


4

Spin was assigned to elementary particles so that conservation of angular momentum would hold in the quantum mechanical framework of elementary particles and nuclei. The Stern–Gerlach experiment involves sending a beam of particles through an inhomogeneous magnetic field and observing their deflection. The results show that particles possess an ...


3

Electrons And Spin From Scientific American Unfortunately, the analogy breaks down, and we have come to realize that it is misleading to conjure up an image of the electron as a small spinning object. Instead we have learned simply to accept the observed fact that the electron is deflected by magnetic fields. If one insists on the image of a spinning ...


1

The solution to this interesting question has to involve both (a) the distortion of the electric field of point charges when they move close to the speed of light and (b) time (since the longer we wait the further apart the electrons become, so their mutual force becomes smaller). Since the electrons are moving along the same straight line we can reduce ...


1

The reason is there is no known force that is strong enough to hold it there. Electrons are quantum particles having very small mass. But we can show how order of magnitude calculations using a minimum amount of quantum mechanics (the position-momentum uncertainty principle) and mechanical energy principles lead to correct order of magnitude results for the ...


1

The probability distribution for finding a ground-state hydrogen atom's electron in some volume is given by $dP = |\psi|^2 d^3x$, where the wavefunction $\psi$ is given by $$ \psi_{n\ell m} = \psi_{000} = \frac1{\sqrt{4\pi}}\frac2{a_0^{3/2}}e^{-r/a_0} $$ where $a_0 \approx \frac12\times10^{-10}\rm\,m$ is the Bohr radius. This is the first of the ...


-3

electrons are like planets revolving around nucleus As centrifugal force and cetripetal force had same magnitudes. When netforce is 0from all directions the particle will start spinning.The same happens for electron and start revolving around the nucleus


0

If you are interested in the physics of solar cells this series of lectures is great. It may at times be over your head but you should be able to get a general idea. But to answer your question: Yes, the electron is excited by the photon and will then travel through the circuit, retaining some of the extra energy that was given to it by the photon. To go ...


2

The electron and positron are two point charges with opposite sign, and classically , as the field lines are an iconal representation of the charge, when the charge becomes zero there will be no electric field lines from the spot where the two point particles overlap. BUT electrons and positrons are quantum mechanical particles and when close enough ...


5

The force between the charges goes to zero. To see this, work in the frame of one of the charges. From its perspective, the other point charge is moving rapidly away, and the field of a moving charge is weaker along the direction of motion, as shown below. One cheap way of seeing this is to pretend the field lines have been "length contracted". For ...


5

In general the wavenumber is a vector. That is, $e^{i(\vec{k}\cdot\vec{x}-\omega t)}$ is a solution to the wave equation in 3 (or any number) dimensions. We say this solution is a plane wave propagating in the $\hat{k}$ direction with wavenumber $|\vec{k}|$ or wavelength $\lambda = 2\pi/|\vec{k}|$. So properly the de Broglie relation is $\vec{p} = \hbar \...


1

This refers to the Feynman rule that crossing fermionic lines produce relative minus signs between amplitudes. That is, if you have some process that is mediated by two different Feynman graphs and one graph is obtained from the other through an odd number exchanges of fermionic endpoints, you must subtract instead of add the amplitudes corresponding to ...


0

Since the electron moves in spacetime and has mass, it produces gravitational waves. that can be derived from General Relativity.


1

Measurements disturb the double slit experiment because of the particle nature of light and matter. In order to measure which slit the electron passes through there must be some sort of interaction to detect the electron. By putting a capacitor in the way, you would drastically affect the particle. Think of it like putting a hose-pipe in front of a ...


0

Charge is conserved, so the equation of continuity should be applied, . It states that the divergence of the current density J (in amperes per square meter) is equal to the negative rate of change of the charge density ρ (in coulombs per cubic metre), Current is the flow of electric charge. So if the divergence of J is positive, then more charge is ...


1

Long ago somebody decided that the direction of "conventional" current flow was the same direction as the direction of flow of positive charges. In that convention the flow of negative charge in one direction is equivalent to the flow of positive charge (and hence the conventional current) in the opposite direction. When introduced electricity usually ...


0

Nothing "flows" actually. Electrons transfer the electrical energy by hitting each other. And even if you consider flowing, only electrons free. Protons cannot because they're held strongly in nucleus. About charge, textbooks usually refers it as positive. That means, we just take the opposite direction of electron flow as +ve charge (because electrons are ...


0

To answer your question we have to keep in mind, that holes are quasi particles. They are a mathematical formalism. They are introduced as empty states in the valence band. From a physical point of view it makes sense to construct these particles, as they really have the properties of real charge carriers. The hole energy is at its minimum at the top of the ...


0

Voltage is the electric potential. As already pointed out by ticster, it is analogous to the gravitational potential, which can be intuited as the height of a hill on earth (higher points having higher gravitational potential). We all know that balls on a smooth hill tend to move toward the bottom. In the case of a ball on a hill, you might also ask, how ...


0

Electricity is not flow of electrons, it is the flow of charge which can be positive or negative. When books tell us that electricity is flow of electrons, they are merely talking about conductors or alloys where only electrons can flow as protons are too heavy to flow. Voltage or the potential difference is generally electric pressure or electric potential....


0

Books tell us that electricity is constituted only by electrons. But in reality protons also cause electricity. In some materials like conductors this is an exception as protons are fixed at their places and are too heavy to move. So basically electricity is a flow of charge which could be positive or negative.


2

With static electricity, the electrons cannot move because the material used is an insulator. Hence there is no current. If the material were conductive, then a current would flow, and there would be no accumulation of charge. Electromagnetic fields will induce a voltage in a conductor, so there will be a current as well. You also need to remember that ...


1

In simple terms it is a matter of scale. The sort of demonstration you see in laboratories have induced emf of a few volts and currents of a few milliamperes. The resistances involved are relatively small compared with those in electrostatic. When static electricity demonstrations are done, for example with the rubbing of glass with fur, the voltages ...



Top 50 recent answers are included