New answers tagged

1

Electrons are accelerated by electric fields. But the story of what happens in a wire is a little bit more complicated. Electrons have thermal energy, and the free electrons in a conductor are moving randomly quite rapidly. At room temperature, electrons are moving somewhere on the order of 10^5 meters/sec. By comparison, the speed of light is about 3 x 10^8 ...


0

Without getting to into the math Potential energy is all about energy/work. Electric fields are about force per unit charge If there is a potential difference from point A to point B of $V_{0}$ volts then this is the amount of work that the field would do on an object per unit charge, if it were to move from B to A. Thus, If there is a potential difference ...


1

The way I understand voltage vs current is that voltage is the potential energy (or force) of the current. The voltage $V$, or potential difference, between two points is the work required per unit charge to move the charge between the two points. It is the potential energy per unit charge, not the total potential energy or force of the current. And the ...


0

I think of voltage as the pushing force of the electrons in a conductor. That's not a bad way to think of it. No voltage, no (bulk) motion. force=m*a That's true for net force and net acceleration. But at the scale of a single electron, (the charge carrier we deal with most often), there are lots of other competing forces. So we don't expect the force ...


1

A proton and electron separately have a total mass-energy of $M = m_p + m_e + U$ where U is the potential energy between them, a negative number. A neutron has mass-energy $m_n > m_p + m_e > M$ Energy is conserved, so spontaneous electron capture is only possible if the nucleus with n protons and m neutrons has a higher energy of configuration than a ...


2

If you supply heat to a fixed mass white dwarf, then less of it is degenerate. The interior of the white dwarf is approximately isothermal because of the very high thermal conductivity of an electron-degenerate gas and is about 100 times the temperature of its photosphere. As you move outwards, the density and hence electron Fermi energy decrease. At some ...


3

But white dwarfs are not expected to shrink! Here is the first plot I could find, from (Soares 2017), showing that for a given mass the radius increases as you heat it: The paper derives a semi-empirical formula originally from Shapiro & Teukolsky that links mass, radius and temperature. This is basically a hydrostatic equilibrium formula, only weakly ...


3

In general relativity, the solution of the Einstein-Maxwell equations for a non-rotating charged black hole is called the Reissner-Nordström solution (references 1,2). It has an electrostatic field in addition to a gravitational field. Far enough away from the event horizon, both effects are well-approximated by the familiar $1/r^2$ force laws. So, to keep ...


1

In quantum mechanics, you don't know the exact position of either electron. So when computing the energy of an orbital, we really compute an average of the energy over possible positions of the electrons, weighted by the probability of each configuration. The ultimate origin of the exchange energy for electrons is the Pauli exclusion principle, which states ...


-4

it seams to me that a low temperature would cause energy to dissipate from the electron orbit. This would more importantly cause the orbit of the electron decrease its distance from the proton/Nucleus core. causing the electron to actually move more quickly around the core. this is the real reason for Thermal Expansion. I find it highly improbable that ...


-2

Consider Bohr's model of the atom, which assumes fixed orbits and trajectories for the electron. Bohr's model of the nitrogen atom is: The problem is, electrons do NOT travel in fixed orbits, and they do not travel with fixed trajectories. Simultaneously known orbits and trajectories violate the Heisenberg Uncertainty Principle.


2

In simple terms initially there is a potential difference across the wires, current flows, due to the high resistance of air, charges will accummalate on the end of the wires, this charge accumulation creates a potential difference to counteract the batteries potential, once they are equal, no current flows


0

It seems to me that the quantum state function evolve continuously as per the Schrödinger equation, but that reflects only the probability of the measurement in a state or the other. The transition itself must be as instantaneous as it can be because a photon is produced, and energy levels in quantum fields being discontinuous, it can only be instantaneous.


0

Why is it said that I = 0 in open circuit . . . This is a steady state condition assuming that the resistance of the open circuit is infinite (very, very high). The processes occurring in a cell are very complex. There is an electro-chemical reaction which results in charges being migrating from one electrode to the other. The imbalance in charge between the ...


0

There is indeed a very brief moment when the wires are attached to the terminals when a current flows, during which the wires are brought to the potential of the terminal. There is no current otherwise, because as you mention the circuit is not closed.


0

A current is created due to the potential difference in a circuit (which means when one side of the circuit has more + charges than the other side (and vice-versa for the other side))), this causes a charge to flow from one side to the other(current). When its open due you think it will ever reach the other side? And even consider that potential drop only ...


1

an electron mostly acts like a wave. An atomic electron spreads out into cloud-like wave shapes called "orbitals". If you look closely at the various orbitals of an atom (for instance, the hydrogen atom), you see that they all overlap in space. Therefore, when an electron transitions from one atomic energy level to another energy level, it does not ...


1

In equation $1.1a$ and $1.1b$ the author states that, $R = V/I$ and $G = I/V$. Which means that $R = 1/G$ (resistivity is the inverse of the conductance). To arrive at equation $1.8$ the author first takes the inverse of equation $1.3$ (mentioned in the text just above equation $1.8$): $$G = G_B \frac{1}{1 + L/\lambda} \to 1/G = \frac{1}{G_B}(1+L/\lambda)$$ ...


1

Bohr model uses "electrostatic forces" that work only for single electron atoms. Quantum theory today uses Schrodinger's equations to understand multi-electron systems. Moreover, Bohr model is actually incorrect, and that's why electric potentials are used to solve problems, since the angular momentum rule that Bohr devised with $mvr = nh/2\pi$ isn'...


-2

The concept of a point particle, however useful in mathematical constructions, introduces trouble when looking at the particle itself. Tricks like renormalization were invented to swipe infinities under the carpet (even Feynman and Dirac admitted that the renormalization procedure is an contrived one, calling for a more "natural" explanation). How ...


0

This question is based on the Drude Model of electrical conduction, which assumes that only the valence electrons contribute to the conduction "sea." I will try to elucidate the meaning of equations 1, 3-5 by using symbols for all the terms. Equation1 gives us a method to find the total number of conduction electrons in the sample (N). This is ...


2

I think you are reading too much into the significance of negative numbers. We need to use numbers in physics to quantify things. Take distance, for example- if I walk from my desk I can qualify the extent of my movement by saying that I have walked 10 metres, say. If I walk another 10 metres to return to my desk, I have walked 20 metres in total, but my ...


1

The picture the author is trying to convey is that if you build a covalently-bonded crystal lattice out of atoms, then the discrete energy levels which characterize the isolated atoms split apart into continuous energy bands. The highest occupied level in the isolated atom becomes the valence band, and the next-highest level (which is unoccupied) becomes ...


1

See the answer by my2cts. If you would like to build some intuition about how quantum orbits are related to classical orbits, basic handwavy arguments about how the classical orbits would behave goes a long way in seeing "why" the probability densities of the hydrogen wavefunctions look the way they do. For example, because any nonzero angular ...


1

There is an interesting post here which I think answers this question: What is the difference between classical and quantum Ising model? For the Ising model specifically, the post says that the dynamics are equivalent to that of the classical problem because all the operators commute with each other.


1

It is possible to understand the situation but the first thing to have clear in mind is that classical intuition based on trajectories becomes useless in quantum mechanics (QM). In no way the quantum description allows speaking about an electron linearly oscillating back and forth. Oscillations refer to a trajectory, while QM is about the expectation values ...


3

Classically a particle without angular momentum will have a radial orbit. This is the closest classical picture to an s-orbital. The orbital is spherically symmetric because the orientation of the orbital is undetermined


0

A bit late to answer your question... Yes, well it is more that there are more phenomena at the minimum of the curve to inelastically scatter the electrons, and the amount of phenomena decreases at very low energies. See also here for more information, and here for a paper in the 80s. TEMs operate at high electron energies mainly because of the obtainable ...


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