# All Questions

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### 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 ...
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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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 ...
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 ...
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 ...
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 ...
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, ...
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 ...
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 ...
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, ...
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### 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 ...
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 ...
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### 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 ...
322 views

### Feynman propagators for scalar fields

If there are few massless scalar field, are the propagators of those different massless scalar fields indistinguishable?
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 ...
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 ...
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 ...
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 ...
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? ...
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?
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### 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 ...
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 ...
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 ...
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) ...
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 ...