2
votes
1answer
74 views

Separating the convective and the inductive electric field

My question is basically this, if I am only able to measure the total electric field and the magnetic field at a few discrete points in space and time, is it possible to separate the convective and ...
2
votes
1answer
106 views

Why water from upper level not goes into lower level in this drainage system

In the following typical water drainage system, I'd like to know why waste water from upper floor (let say, from 2nd floor's toilet) does not come to the lower floor's equipment via the common pipes ...
2
votes
2answers
103 views

The physical interpretation of Newton's constant $G$

It is well known that the speed of light $c$ can be interpreted as the speed limit for information propagation. Similarly, the Planck's constant $h$ is interpreted as the minimum quantum package of ...
2
votes
1answer
97 views

What is the appropriate device for measuring energy loss from collision with surface?

The surface of a running track (i.e. cinder or rubber) has an effect on a runner's performance. I would like to get some device for measuring how much energy a runner loses on each surfaces. I've ...
2
votes
1answer
69 views

Compatibility conditions of spinors and Riemannian Metrics

I came across an interesting article by Montesinos (J. Geom. Phys. 2 (1985), no. 2, 145–153.). In it, he finds that spin structures (as lifts of $SO(4)$) are not compatible with all Riemannian metrics ...
2
votes
2answers
1k views

Deriving torque equation from Newton's 2nd Law

I'm trying to understand the derivation of the torque equation $\vec{r} \times \vec{F} = I \alpha$. My textbook derives this easily enough from Newton's 2nd Law for a single point with mass $m$ and ...
2
votes
1answer
118 views

what is the mechanism of water conductivity?

I'm trying to wrap my head around the kelvin water drop generator and more specifically what happens in the water before it drops. If on one side the drops of water are positive and on the other side ...
2
votes
1answer
110 views

Problem with relativity of acceleration

In this answer http://physics.stackexchange.com/a/92833/36977 John said that acceleration is not relative in the general theory of relativity. But as we all know, accelerating charges emit ...
2
votes
1answer
172 views

Contradicting forces on a circular loop under current in magnetic field?

I have the following general conceptual concern. Think of a thin conducting loop of radius $R$ placed in the $x$-$y$-plane at $z=0$. There is a homogeneous current density $\vec{j}$ running through ...
2
votes
1answer
402 views

Energy dispersion in graphene

Given that graphene has linear energy dispersion near the Fermi level and the dispersion is given by $E=\hbar \nu_F|\vec{K}|$, I would like to determine the density of states. I think it is equal to ...
2
votes
1answer
1k views

Can a macroscopic body have wavelength as that of electron? [duplicate]

Einstein has suggested that light can behave as a wave as well as like a particle i.e, it has dual character. In 1924, de-Broglie suggested that just as light exhibits wave and particle properties, ...
2
votes
1answer
155 views

Can two spools shield you effectively against radiation

a friend of mine thinks that by buying a product called rayguard he can effectively shield against electrosmog. On the website, there are multiple evidences that this might work. However the product ...
2
votes
1answer
92 views

Why would the environmental lapse rate be slower near the ground?

I have data taken from over 2300 ascents through the atmosphere at various locations around the world, for every 500 meters vertically upwards I have averaged the temperature and plotted it: Its ...
2
votes
3answers
4k views

Realistic calculation of heat loss for pipe

Good day everyone, I am new on this site and I hope to find here help, since I am not going anywhere with the literature I have found. I try to calculate realistically the heat loss of a hot, ...
2
votes
1answer
80 views

Will a space traveller slow down due to space expansion?

Photons of relic radiation loose their energy as they propagate through space. Will a space traveler loose their peculiar velocity as he travels through vast distances? Will he stop somewhere or still ...
2
votes
1answer
365 views

Edge states in the “half BHZ” model

Consider the "half BHZ" Hamiltonian $${\cal H}=\sum_{\mathbf{k}}\left(A\sin(k_{x})\sigma_{x}+A\sin(k_{y})\sigma_{y}+{\cal M}(\mathbf{k})\sigma_{z}\right)c_{\mathbf{k}}^{\dagger}c_{\mathbf{k}}$$ where ...
2
votes
1answer
338 views

Pauli-Fierz “massive” equation and linearized gravity

It it known that the massive spin-2 irreducible representation of the Poincare group is the traceless symmetrical transverse 4-tensor $h_{\mu \nu}$ with rank 2: $$ (\partial^{2} + m^{2})h_{\mu \nu} = ...
2
votes
1answer
85 views

Optical coherence tomography

In Optical Coherence Tomography, Broader bandwidth/low coherence light sources are used. Is it only because to increase the resolution or are there any other reasons? What will happen if we use a high ...
2
votes
3answers
162 views

Does electromagnetic radiation make sense in one dimension?

I'm trying to do a simple simulation of a 1D charged quantum particle, which gets irradiated by an electromagnetic wave — in context of non-relativistic QM. The Schrödinger equation for such a ...
2
votes
2answers
297 views

Wave function for an electron in and around a small charged sphere

I am interested in solutions of the Schroedinger equation. For simplicity I started my studies with the $n=1$ ground state of the hydrogen atom. I was particularly interested in the higher moments of ...
2
votes
1answer
394 views

Lorentz group representation and transformation of “vectors”

Let $P$ be the parity operator of the Lorentz group, $$P=\begin{pmatrix}1&0&0&0\\0&-1&0&0\\0&0&-1&0\\0&0&0&-1\end{pmatrix}$$ the commutation relations ...
2
votes
1answer
144 views

Why does cloud-ground lightning occur so much less frequently over ocean?

I was talking with an acquaintance about lightning, and we came up with opposite theories and predictions for the frequency of lightning over ocean. My theory is that since seawater is a fluid ...
2
votes
1answer
380 views

A question about Fermi-Dirac Distribution function

It seems more like a mathematical question, about the property of Fermi-Dirac Distribution function $$f=\frac{1}{e^{(E-\mu)/k_BT}+1}$$ where $\mu$ is the chemical potential and $k_B$ is the Boltzmann ...
2
votes
1answer
214 views

Acceleration of particles in a pipe with variable cross section

I am currently making an exercise from Paterson,1983, IV.3.ii. It goes as follows Water flows steadily and incompressibly along a pipe whose area cross section $A(x)$ varies slowly with the ...
2
votes
1answer
86 views

Steam bath physics

In the steam bath at the health club, why is the "steam" thicker first thing in the morning before it has been used all day and the walls are "hotter"?
2
votes
1answer
81 views

Frequency dependence of permittivity — why not monotonic?

I naively thought that most materials were transparent to radiation of frequencies above their plasma frequency, and opaque to radiation below it. The most intuitive (and analyzed lightly in ...
2
votes
1answer
83 views

Logarithmic intensity formula factor?

In formulae for sound intensity and sound pressure, there is a logarithm part for the logarithmic increase of the quantity we're studying, and also a numerical factor 10 or 20 depending on the ...
2
votes
1answer
193 views

Name for thermodynamic derivative $dP/dT|_V$?

While trying to express the isoentropic sound speed as partial derivatives of $V$ and $T$ only I end up, as part of the longer expression with $dP/dT|_V$ (which according to a Maxwell relation is the ...
2
votes
1answer
164 views

some questions regarding Doppler shifting versus absorption-emission

I just got in what I thought was a silly exchange where a self-identified physicist states that the difference between "red-shifting" (in the Doppler sense) and the re-emission of light at longer ...
2
votes
1answer
146 views

Does there exist electric field around all the substances?

A system of two equal and opposite charges separated by a certain distance is called an electric dipole. Electric dipole moment ($p$) is defined as the product of either charge ($q$) and the ...
2
votes
2answers
234 views

Actual meaning of “Gravitational Potential”?

In a gravitational field, the gravitational force acting on a body (of mass m) at a point x metres away from the attracting body (of mass M) is $\frac{GMm}{x^2}$. Integrating this force from a point ...
2
votes
1answer
128 views

Do I need to take elastic potential energy into account? [closed]

Let's say I have a vertical spring with end points $A$ and $B$ and length $a$ and a mass attached to the endpoint $B$. The mass is dropped from the point $A$ and I need to find the kinetic ...
2
votes
1answer
769 views

How does repulsion and attraction of a magnet work?

How does repulsion and attraction of a magnet work? I have a hypothesis. We all know that repulsion works when people throw balls at each other. This is used as an analogy of how virtual particles ...
2
votes
1answer
82 views

Slowing of photons in a EB Condensate

Help me understand this. I have heard tell that they are now able to slow the forward progress of a photon traveling through an EBC to somewhere near 35mph. Is this actually the physical slowing down ...
2
votes
2answers
921 views

Circularly polarized light incident at Brewster's Angle

If a perfectly circularly polarized wave of light is incident on a dielectric medium (coming from air) at Brewster's Angle, what will the polarization state of the transmitted wave be? I am aware ...
2
votes
1answer
185 views

What to do with a $\phi$ term in a Lagrangian?

I am considering a Lagrangian that is of the following form: $$\mathcal{L}=-{1\over 2}\partial_\mu\phi\partial^\mu\phi+2\mu^2\phi^2+2\sqrt{6}{\mu^3\over \lambda}\phi + {9\mu^4\over 2\lambda} + ...
2
votes
1answer
140 views

Solving Systems of Partial Trace Equations

Say I specify a quantum state - pure or mixed - by its partial traces on various subsystems. To what degree could one recover the original state, and what are the known methods for doing so? For ...
2
votes
1answer
322 views

Feynman propagators for scalar fields

If there are few massless scalar field, are the propagators of those different massless scalar fields indistinguishable?
2
votes
1answer
135 views

Ring Resonators

If optical field will propagate into the following ring resonator. Optical field will propagate into the ring and propagate to the coupling region. I didn't get where and how the interference will ...
2
votes
1answer
407 views

Absorption of a gas into a solid

When a gas interacts with a (crystalline) solid, some scenarios may happen: scattering: gas atoms will not stick or penetrate (do not interact with the solid) Adsorption: gas atoms stick to the ...
2
votes
2answers
1k views

How to interpret band structures

I'm currently taking a Solid State Physics class, and is currently reading about the quantum mechanical description of solids. I then came across the following figure: It's supposed to be the band ...
2
votes
1answer
1k views

Deriving expression for motional emf

I'm having a trouble deriving the expression for emf caused by the Lorentz forces in a moving conductor. Consider the following classical example of a slidewire generator which consists of U-shaped ...
2
votes
1answer
105 views

Steps involved in photon emission [duplicate]

What are the detailed steps involved in the emissions of a photon, for example, when an electron drops to a lower energy level? How well do we understand the production of the photon in this example? ...
2
votes
3answers
143 views

Electromagnetism: Conductors

Even though the thermal velocity of electron in a conductor is comparatively high, the thermal velocity is not responsible for current flow? Why is this the case?
2
votes
1answer
79 views

Why must the final state be stationary?

I faced the following sentences: We consider a gravitational collapse taking place in this spacetime. The singularity theorems assure us that a singularity will form. The assumption that the ...
2
votes
3answers
570 views

Reflections in Rearview Mirror

Why is it that in the reflection in the rear view mirror of your vehicle in the car behind you The driver is on the drivers side and the passenger is on the passenger side and when they raise thier ...
2
votes
1answer
641 views

Geometriclength and effective length

Why is effective length of a bar magnet shorter than its geometric length? Blockquote in a textbook, author wrote that, effective length is equal to 0.85 times geometric length. But didn't ...
2
votes
1answer
59 views

Why is it possible to expand the SM Higgs field in its second component only

In the lecture, the professor said something along the lines of: "After a suitable gauge transformation, the standard model higgs field can be expanded as $$\phi =\left(\begin{array}{c} 0 \\ v+H(x) ...
2
votes
1answer
161 views

If charged particles always attach to black hole event horizons, how can ordinary matter fall in?

(A friend at work kindly loaned me loaned me his copy of Kip S Thorne's "Black Holes & Time Warps". This may have been ill-advised... :) BH&TW 1994 paperback p.410 Figure 11.5: ... all ...
2
votes
1answer
97 views

Why the uncertainty principle can be used for estimation?

It is usually said/done in textbooks and classes that if $\Delta x$ is known then $\Delta p_x$ can be estimated using the uncertainty principle as $\Delta p_x \sim \hbar/\Delta x$. But the ...

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