# Tag Info

-3

this may follow einsteins equation and may appear to fit into classical picture , but this is taking place between two particles obeying fermi dirac statistics hence it is a quantum phenomena and the direction of photon emission is arbitrary as required by the fundamemntal assumption of quantum mechanics

15

It is a standard exercise in quantum electrodynamics to find the angular dependence of the differential cross section. Which more or less means how probable it is for the photons to scatter at a certain angle, given the energy of the incident particles. So assuming the spins of the electron-positron pair is averaged, and that you don't care about the photon ...

1

In a lit candle, when gaseous candle wax reacts with the oxygen in the air, the atoms will be unstably excited. To be stable, the excited electrons will relax to the ground state by emitting photons with energy equal to the energy difference between the 2 states. The photons’ energy doesn’t change much, so the wavelength doesn’t change much. The chemical ...

0

To say I am skeptical would be an understatement. I briefly worked on this around 1997 and what I see here, although it matches his description of what he wanted, in no ways matches the effects he claimed for his "original" which exhibited massive positive feedback, ionization, extreme cooling and massive antigravity effects. The over-unity claims were just ...

0

Even if the electron is acted upon by a torque $\vec{\tau} = \vec{\mu} \times \vec{B}$, how does it deviate the path of the incoming electrons? To do such a task, you need a force. Where does that force come from? The force comes from this equation: $\vec{F} = -\vec{ \nabla }U$ where $U = - \vec{\mu} \cdot \vec{B }$. If the magnetic field $... 0 Electron orbitals are more than just orbitals... it's really best to think of it as a shell, rather than an orbit. The Heisenberg uncertainty principle comes to play, stating the the electron doesn't orbit, but rather it is positioned at the nucleus with an uncertainty amounting to the size of the shell. The size of that shell can change if the electron ... 2 It will help if you study this diagram of what a vacuum tube is If a cathode is heated, it is found that electrons from the cathode become increasingly active and as the temperature increases they can actually leave the cathode and enter the surrounding space. When an electron leaves the cathode it leaves behind a positive charge, equal but ... 0 No, they don't. Only some of negative particles (electrons) on the top shell could do that. Atomic nuclei together with inner electronic shells do not move (almost). In metals they form kind of crystalline cubic grid. 0 Since superconductor is a conductor of electricity, the electric field of the electron should repel electrons in the superconductor, thus making the superconducor itself have an electric field that attracts the electron. 2 The energy is: $$E = \frac{n^2h^2}{8mL^2}$$ Your mistake is that you have$L$not$L^2$in the denominator so your answer is a factor of$L$too small. 1 A single charged object is sufficient to produce an electric field. Following Coulomb's law:$\textbf{E} = {Q \over 4\pi \epsilon_0\textbf{r}^2}\hat{\textbf{r}}$where$\textbf{E}$is the vector electric field, Q the charge of the object in question,$\epsilon_0$the permittivity of vacuum or the electric constant,$\textbf{r}$the vector position of the ... -1 An electron is a tiny charge that revolves at the speed of light in a Compton wavelength circumference orbit. If you calculate the current of that charge as it passes an observer near the orbit, and then the area of that orbit, you can calculate the magnetic moment, which is the Bohr magneton, identically. The mass is contained in the field of the ... 0 Atoms and small molecules have discrete energetic states. When an excited molecule relaxes to the ground state by emitting a photon, the energy (wavelength) of this photon is equal to the energy difference between the 2 states. 0 Think of charges as a bunch of$+1$s (protons) and$-1$s (electrons). It doesn't matter how many$0$s (uncharged particles) we have because$0 + 0 + 0 + 0 +... +0 = 0$. Now in most cases it's pretty difficult to change the number of$+1$s a body has, so we can see if it has more$-1$s than$+1$s to know if it's negatively charged or not. Let's call the ... 0 Yes. And because those energies correspond to differences in energy between bonds in CH and C2 and bonds in the CO2 and H2O reaction products. 0 Exept that alpha particles are much heavier than electrons and it wouldn't make sense for them to change the direction when in contact with electrons, the point of the experiment was that, because of the deflected alpha particles ONLY in a very tiny, central area of the atom, most of the atom space is EMPTY. This conclusion wouldn't been made if alpha ... 4 This is quite an interesting question. First - air is a (poor) conductor. See this earlier answer for some details on how well (or poorly) air conducts (especially when the relative humidity increases). Next - vacuum as an insulator. You are right that once electrons are "in space", a vacuum doesn't provide much impediment. This is why cathode ray tubes ... 2 The same question could be asked about electrons in atoms. Why on Earth do they remain bound to the nucleus instead of floating around freely? The answer to this question and to yours is that the nucleus (in the case of atoms) and the metal (in your case) is offering a quite cozy place for the electrons to be and leaving it is quite costly in term of energy. ... 1 Einstein was quoted as saying 'You know, it would be sufficient to really understand the electron'. We understand the electron, but we do not really understand it. The intrinsic spin, the magnetic dipole moment and the relation to the positron are not really in full grasp. We are lucky that nature does not play dice- again by Einstein, and this is how we get ... 2 There is an example in which it is not clear which forces act there, but I am not sure if you learnt of such things. I'll try to make it simple. In the quantum physics we know to prepare sets of particles in what is called entanglements. Such an example is the so-called singlet of polarization of photons. Polarization is how oscillates the electric field in ... 1 If you ask me , what IS an electron, I don't know. Some people might say, without being allowed to describe its properties, it's a meaningless question. My answer would be always to describe it in terms of it's properties, i.e as you say, by means of its forces. So, yes, I would agree with you, if all matter is made up of elementary partices and we can only ... 1 I'm not actually familiar with the construction of these microscopes, but most devices using focused charged-particle beam rely on quadrupole magnets1 to maintain the control of the beam size and shape. It is worth noting that a quadrupole that focsuses the beam in one plane tends to de-focus it in an orthogonal plane, but by using sets of multiple ... 3 Rutherford modeled the atom as an extremely compact positive nucleus surrounded by a uniform ball of negative charge the "size" of the atom. He included the effect of scattering by the electrons under the assumption that they acted like such a diffuse cloud of negative charge, and showed that such a cloud had negligible probability of scattering the alpha ... 0 The theory of the above two answers is correct, but the equations provided are not quite correct. The equation $${{1}\over{2}}m_e(v_T)^2 = {{3}\over{2}}k_BT$$ is based on the assumption that the electrons behave as an ideal gas (and is true for semi-conductors). However, in metals, electron velocity actually has a very small dependence on temperature, and a ... 0 Influence of internal EM forces on the sphere cannot be calculated based on the field momentum outside the sphere - it is more complicated since the field is not simply moving with the sphere when the sphere moves in a general way. Also, the electromagnetic defect is present, but it is explainable purely with mutual EM forces. No effect of zero-point field ... 1 this electromagnetic mass$m_{elec}$has to be added to the standard "mechanical mass" of the sphere to give the total observed mass of the object. Would this view be accepted by most physicists today? That is a wrong idea. Why? There is no reason (in this case) to count quantity$m_{elec}$, defined based on EM momentum distributed in the whole ... 2 It is indeed the case that the Casimir force for a three dimensional sphere is repulsive. http://arxiv.org/abs/hep-th/9406048 Neither myself nor the authors of this paper know an intuitive explanation of why this is the case. It is important to remark, however, that this result actually disproves the naive and very common "mode counting" argument that ... 0 I don't have access to the Sampayan paper, but I think you're conflating two different things: The total anode-to-cathode accelerating potential$V_{AK}$. (Note it's the difference between the two potentials that matters.) The cathode is assumed to be capable of emitting unlimited numbers of electrons, so it is solely the repelling electric field of said ... 1 Note that there is an effect on the electrons that is much larger than caused by direct interaction with the alpha particle. If the alpha partcle collides with the nucleus then the nucleus will change its momentum. To a good approximation this is an instanteneous change and then the so-called "sudden approximation" applies to the electron state. So, the ... 0 I don't think that would be possible since there is vacuum outside of the electron as well, everything between the electron and the nucleus is vacuum. 2 Electrons can deflect a heavy alpha-particle backward if they are sufficiently energetic. There are such electrons indeed, but their concentration is very small, I guess. -1 Backscattering requires a repulsive force while an electron would attract the alpha particle. Furthermore, the electron is lighter than the alpha particle : in a collision between a truck and a mosquito, the truck doesn't rebound at all. EDIT : unidimensionnal motion (ie. the particle moving back and forth on the same line) requires a repulsive force, but ... 5 "The wave is actually probability in the sense that it assigns probability to the space coordinates of detecting photon at a certain time." No, the emergence of the classical EM wave from the quantum wavefunction of the photon is not trivial, because a classical EM wave is made up of many photons. In particular, it is not the case that the classical EM ... 3 "The wave is actually probability in the sense that it assigns probability to the space coordinates of detecting photon at a certain time. Now, the wave transports energy & momentum." As you say that you quote words from a book, then, you have to know that there are many books and many authors, each one with his/her opinion. There are four basic ... 2 The key difference is that the alpha particle is several thousand times heavier than the electron. It would be like you rolled a bowling ball at a marble and it bounced backward. As Rutherford said: "It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of ... 2 The gravitational force is a very weak force it cannot compete with the electromagnetic forces which create all observed matter. In addition to the neutrality of all matter, that there are positive charges in the nuclei with electrons around them, the framework is quantum mechanical. There are always spill over positive forces that attract and keep ... 1 What force keeps electrons to fall on the ground and discharge the wire? The electromagnetic force. Electrons want to get away from each other, but they want to be near the positively charged nuclei with which they form atoms. Even in a metal, where the electrons are weakly bound to the positively charged ion cores, those positive charges are still ... 0 A book on semiconductor devices in general, like this one (e.g. section 2.7), may help. Also, just look at the diagram at the right of this Wikipedia page. In general, imagine that we're looking at a graph of different energies (usually shown on the$y\$ axis) in this semiconductor. The big thing that you'll notice in a semiconductor is that the density of ...

1

The answer lies in a thermodynamic argument. The diffusion is a spontaneous process that occurs when particles with random motions are not uniformly distributed. The electrons in the conduction band in the n region are much more numerous that in the p junction. They will naturally tend to balance the concentration from the n junction to the p junction since ...

4

What happens with static electricity on a shirt is, if it comes into close proximity to another surface, the difference in electrical potential can become greater than the breakdown voltage of air. Then, current flows through a small electric arc, which is a plasma of air molecules and electrons. Very locally, this has a much higher temperature than the ...

0

Related: What's the reason behind calling cathode rays tube by the name cathode? Short answer: the voltages accelerate the electrons away from the cathode so that they hit the screen (anode). You actually have two anodes, one a tiny bit behind the cathode where the electrons come out. This one has a hole where the electrons can fly through. A second ...

0

It's basically just an electrical circuit. The interesting part is that a portion of the circuit has no wire, but is a bare electron flying through the CRT. It lands in a particular spot and collectively, many such electrons can form a picture, due to the retained glow from the phosphorus screen.

1

Yes, this is actually often used in a spectroscopic technique called REMPI -- see the image on this wikipedia page https://en.wikipedia.org/wiki/Resonance-enhanced_multiphoton_ionization There are some important physics techniques that rely on interaction with two photons -- two photon spectroscopy (http://cua.mit.edu/8.421_S06/Chapter9.pdf). Some other ...

1

(Moving this from my comment to an answer) Yes, the electric field simply penetrates the glass wall and charges (the electrons) placed in that field will feel a force and move. The glass does not really interact with the charges on either side, so you might as well remove it completely (theoretically).

4

You are probably thinking in terms of the shell model of the atom: (source) It is important to note that the shell model is ultimately inaccurate and is not really a good representation of how modern physics views atomic structure. It has a few advantages, and it is a nice tool to explain certain features in atomic structure (in particular, the fact that ...

2

If you have current flowing one way through a resistor, then the electrons flow through the other way. Since current flows from the high voltage end of a resistor to the low voltage end, then the electrons come in at the low voltage end and come out at the high voltage end. When electrons (which are negatively charged) go from low voltage to high voltage, ...

0

There may be a confusion between enery and power. While the current, which is the number of charges per second, and the energy of the ,electron do'nt change at the output of the resistor, the power does. Power is the amount of energy per unit time, and that does not affect the current which, again, is the amount of charge per unit time.

2

An electric current is the flow of electric charge. But electric charge is not an entity, it is a property that must be 'carried' by a charge carrier. An electron current, the flow of electrons, contributes to an electric current since the electron 'carries' negative electric charge. However, an electric current is not necessarily an electron current. ...

4

There are a number of ways to represent a 720 degree spin of a particle, but the particle has to be a little more complex then a spinning ball. Imagine this wiki image (from http://en.wikipedia.org/wiki/Spin-1/2) as the inside of a larger ball and you can see an example of 720 degree spin. My favorite representation is the idea of breaking the electron into ...

Top 50 recent answers are included