All Questions
227,290
questions
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How to calculate the function giving the angle of an oscillating axle?
Suppose we have a rod of length $r > 0$ and we attach to one end of it an object of mass $m > 0$. Also, we attach the second end to a static location. Finally, we are given a friction ...
- 135
0
votes
0
answers
6
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Are Transmission values for absorptive light filters proportional to Intensity?
Mostly filter rates are given in percent, but if I imagine that for example 10 photons hit an absorption filter with 50%, molecules are excited there and in the end only 5 get through while the other ...
- 137
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0
answers
11
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Two space crafts A and B travel towards each other at 90% of the speed of light. What does A observe on B and B on A?
This is an extention to the "twin paradox". Suppose that two space crafts A and B travel towards each other at 90% of the speed of light. There is an observer C on earth. We know that from C'...
- 101
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0
answers
6
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Why is the electric field time independent in the induction equation of the magnetohydrodynamics?
Why does the induction equation of the magnetohydrodynamics assume the electric field $E$ is time $t$ independent or $\frac{\partial E}{\partial t}=0$?
- 818
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0
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14
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Depletion Region of PN junction
In the depletion region of the PN junction diode, charge carriers are negligible but there is charge density. How?
1
vote
0
answers
20
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Trying to derive chiral anomaly in 2D from Feynman diagrams in position space
Trying to understand the Chiral anomaly, I decided to explore the simplest example of a holomorphic fermion in 2D in a background electromagnetic field $A\text{d}z+\bar{A}\text{d}\bar{z}$. The ...
- 3,795
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votes
0
answers
15
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SOLID STATE (FCC LATTICE STRUCTURE) [closed]
How many atoms per mm2 surface area are there in (110) plane for lead which has FCC structure. The radius of atom is 0.74nm.
I'm not able to proceed
- 1
0
votes
2
answers
31
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Different Bernoulli equation from $F=dp/dt$ [closed]
If any part of the question needs clarifying, there might be explanation in the post-script and of course ask if needed.
I understand how the Bernoulli equation is derived for incompressible fluid in ...
- 78
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votes
1
answer
18
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Consider an infinite solenoid in wich a sinusoidal current flows, is the potential energy stored inside the solenoid a conservative energy?
If it is not, could you still add this energy term in a Lagrangian ?
- 1
-4
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0
answers
32
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Is my conceptual general theory model of The Universe as fundamentally micro-particulate possibly viable? [closed]
Suppose that at creation material particle mass was around 2 x 10^-87 and there were several types. That a large amount of material was expelled at below c, but then things got going and following ...
-3
votes
1
answer
70
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How to know which states are entangled from a state vector?
consider the following state vector of three qubits
$$(1/2)|000⟩+(1/2)|011⟩+(1/2)|101⟩+(1/2)|110⟩.$$
how to know which qubits are entangled with respect to their basis states, in other words, how do ...
2
votes
2
answers
103
views
What kind of coordinate change is needed to make gravity disappear?
I understand that the Christoffel symbols associated with the metric will vanish locally once you perform the appropiate change of coordinates. These new coordinates correspond to an observer in free-...
- 51
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votes
2
answers
103
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Superposition and Electrons
I was watching the following video here. It discusses the electron spin quantum number $m_s$. It then discusses that an electron may be classified as having spin up or spin down. From what I ...
-1
votes
0
answers
15
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Analyzing the angular frequency of an oscillating charged mass [closed]
A small puck of mass m carries a negative
electrical charge –q. It slides on a frictionless horizontal
surface, which is a distance a above a postiive charge +Q, as
shown, so that the equilibrium ...
0
votes
2
answers
70
views
Difference in spin angular momentum
In chemistry, I learnt that the spin angular moment of a single unpaired electron in an atom can be calculated by
$\frac{\sqrt{3} h} {4\pi}$,
but while studying radioactivity, I studied that the spin ...
- 72
4
votes
1
answer
28
views
Expressing a specific motion from the point of view of a different rotating coordinate system [closed]
Simplified problem presentation
I am trying to describe a specific motion from a point of view of a moving coordinate system. To make easier the comprehension I created this childish animation, where ...
- 41
1
vote
0
answers
40
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Energy-momentum tensor of Majorana field
The Majorana field action in curved spacetime, in general, is usually written as
$$\mathcal{A}_M = \displaystyle\int_\mathcal{M} d^4x ~ e \left\{\dfrac{1}{2} \bar{\psi}\Gamma^\mu D_\mu\psi - V\left(\...
- 664
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votes
1
answer
17
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Effect of pipe size on water flow rate in municipal water system [closed]
i am expanding my house and the town is requiring us to increase the size of the water line from the street from 3/4 inch to 1 inch diameter.
intuitively i understand that a bigger pipe results in ...
-1
votes
0
answers
69
views
Applying an operator on both sides of an equation
I am doing a quantum mechanics question involving the positivity of the norm. So I'm using the fact that the norm will be greater than zero but i want to apply an operator onto the ket on one side of ...
- 19
0
votes
2
answers
33
views
Field of Inertial Forces
Although inertial forces are just our mathematical creation to help apply Newton's law even in non-inertial frames, can we assume or is it (mathematical proof) that inertial forces also create its ...
- 53
1
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0
answers
19
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Why Faraday homopolar generator need brushes?
It is said that if one would attach a load physically to the rotating disc from center to rim no current would flow because both in the load wires and the disc itself currents would be generated in ...
0
votes
1
answer
19
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Normal derivative of a sheet current
Let's say we have a closed surface $\Gamma$ with a local unit normal vector $\mathbf{n}$, where a surface current (electric surface current) $\mathbf{J}_s$ lies on $\Gamma$.
The normal derivative (...
0
votes
0
answers
23
views
Kinetic mixing, and a bare mass?
I've been reading the following classic paper by Bob Holdom "Two U(1)s and $\epsilon$ charge shifts", and I'm attepting to derive the expression for $\chi$. In particular, I am computing the ...
- 1,231
4
votes
0
answers
65
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About the traditional explanation of the continuity of the first derivative of a 1D wavefunction
I would like to receive some clarifications about the traditional explanation of the continuity of the first derivative of a 1D wavefunction (E.g. see the very clear answer by @ZeroTheHero ...
- 67.9k
-4
votes
1
answer
101
views
Do chargeable batteries break the third law of newton? [closed]
When you charge a lithium battery for instance the electron momentum that coming out of the source is stored in the battery. The problem is that the direction of the electron might change when ...
- 147
0
votes
0
answers
17
views
Thermal motion at higher pressures at constant temperature
I would like to know if the thermal motion of molecules stays constant if the pressure is increased at constant temperature or not. The viscosity increases with pressure, thus the friction between the ...
0
votes
0
answers
21
views
Transfer matrix solution of Heisenberg model
While reading G. Mussardo's Statistical Field Theory: An Introduction to Exactly Solved Models in Statistical Physics, I found that the six-vertex model is equivalent to the Heisenberg Spin chain and ...
- 531
2
votes
1
answer
41
views
Similarity between holonomic/nonholonomic constraints and state/path variables in thermodynamics
I have recently learned about holonomic and nonholonomic constraints in analytical mechanics, and how they can be expressed as exact (Pfaffian form); for example:
$${\displaystyle df_{i}=\sum _{j}\ A_{...
- 39
9
votes
1
answer
254
views
QM from the uncertainty principle?
In a book Quantum Mechanics with Applications (1970) by D.B. Beard and G.B. Beard, the authors wrote on page 34:
"By methods beyond the scope of this text, one could state the uncertainty ...
- 679
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votes
2
answers
38
views
Relationship between volume and temperature of an ideal gas
I am self-studying thermodynamics, and was reading up Carnot heat engine (Yunus Cengel - thermodynamics book). So, the experiment in the textbook is set up such that, we have an adiabatic piston-...
1
vote
1
answer
92
views
The Work-Energy Theorem in Non-Inertial Frames: A Critical Analysis and Misconceptions
It is evident from these queries and responses that the Work Energy Theorem holds true in non-inertial frames (with work performed by pseudo force included in the equation).
Is work-energy theorem ...
- 374
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votes
1
answer
25
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Minimising losses in an optical resonant cavity
I am doing a question and I am asked to calculate the radius of curvature of two identical mirrors at either end of an optical cavity in order to minimise the losses in the cavity. Is the correct ...
- 19
0
votes
0
answers
26
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Determine number of objects in box by shaking
Given a container filled with identical objects, how could I find the number of objects in the container accurately purely by analyzing the sound produced on shaking? More specifically, which acoustic ...
- 1
0
votes
0
answers
39
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Tensor transformation example with Kronecker delta (Preliminaries - Quantum Field Theory for the Gifted Amateur)
In (1) eq. 20 the author writes the transformation properties of a tensor
$$
\bar{T}^{i^\prime \dots k^\prime}_{l^\prime \dots n^\prime} = \frac{\partial \bar{x}^{i^\prime}}{\partial x^{i}} \dots \...
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votes
0
answers
30
views
Help solving this mechanics problem [closed]
Between a push cart and a pull cart, which requires the greater "effort"? For consistency, both weighs 500 N, has a handle bar inclined 30° above the horizontal and a coefficient of sliding ...
0
votes
0
answers
14
views
Beam diameter of a fluoresence emitter after an objective
I try to calculate the beam diameter after a high NA objective that focuses on a point-like emitter that emits fluoresence light.
To my basic understanding, I get this by computing the Entrance pupil (...
- 131
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votes
0
answers
38
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Problem with an extra term in the von-Neumann equation
I have recently started studying quantum systems with mixed states, and I have come across with the von-Neumann equation. I could derive it by making the time derivative of the explicit form of the ...
0
votes
0
answers
58
views
Where does the Quantum single-particle Lagrangian come from?
In Mahan's many body physics the Lagrangian is simply given as
$$L=i\hbar\psi^\dagger\psi-\frac{-\hbar^2}{2m}\nabla\psi^\dagger\cdot\nabla\psi-U(\textbf{r},t)\psi^\dagger\psi$$
I'm trying to derive it ...
- 303
1
vote
1
answer
83
views
Time derivative term in Navier Stokes equation for fluid in porous media
I was reading the research paper Homogenization of peristaltic flows in piezoelectric porous media and came across the hydrodynamic equation:
$$\mu \nabla^2 v^f -\underline{ \rho_f (\dot{v}^f + w \...
- 270
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0
answers
22
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Is the electric flux from the antenna able to exist without connecting electric charge?
https://en.wikipedia.org/wiki/Radio_wave#/media/File:Dipole_xmting_antenna_animation_4_408x318x150ms.gif
According to above figure, the electric flux is in the close loop state like a balloon and is ...
- 21
0
votes
1
answer
975
views
Ground state of the Heisenberg XXX model with a coupling?
I have a one-dimensional Heisenberg chain with a Magnetic field with $N$ sites with $J>0$
\begin{equation}
\mathcal{H} = -J \sum_{i = 1}^{N-1} \vec{S_i}\cdot \vec{S_{i+1}}- \sum_{i = 1}^N \vec{H}\...
- 531
1
vote
0
answers
24
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Will a persistent supercurrent in a superconducting aluminum ring decay if the ring is connected to a non-superconducting aluminum wire?
Will a persistent supercurrent in a superconducting (SC) aluminum ring decay, if we connect the SC aluminum ring to an aluminum wire and the remote end of the wire is located in a separate chamber ...
0
votes
2
answers
48
views
Head to tail rule of vector addition
Can then resultant vector pass through the vectors being added? Does the order in which place vectors according to head to tail rule matter?
let's suppose that vectors A and B are pointing east while ...
- 1
0
votes
1
answer
42
views
Where does the force that resists changes to an objects geodesic path in empty space come from?
assuming an object is free of a gravitational field and following its geodesic. Applying a force would be changing the 4 vector momentum of the object relative to the frame the object was in before ...
0
votes
0
answers
36
views
Why don't they use golf ball dimples on cars? [duplicate]
Just watched an episode of mythbusters where they proved that a car got better fuel economy with golf ball dimples. So why don't they use that on cars?
0
votes
1
answer
54
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Newton's second law - local laws and non-local laws
What are local laws? I was reading this line in a book...
Newtons second law is a local law. This means that it applies to a particle at a particular instant without taking into consideration any ...
0
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0
answers
35
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How does changing the mass of a block affect its speed after collision? [closed]
I'm doing a physics IA investigating how mass of a block affects it's velocity after collision when initial momentum is constant. I did this by using a pendulum setup with a constant release angle (...
2
votes
0
answers
70
views
How does QED describe the electromagnetic scattering between two neutral fermions?
Fermions with no electric charge may carry magnetic moments e.g., the neutron. Since particles with magnetic magnetic moments interact, they're expected to scatter off each other electromagnetically. ...
- 11.1k
-7
votes
0
answers
37
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With respect to [closed]
e-mc^2. What is light in between. What type of essence is it before it becomes energy? How does it appear or does it, like an event horizon, suddenly change over?
0
votes
1
answer
30
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Why does this coin disappear from bottom up?
I happened upon this video purportedly showing a coin on a horizontal table receding away from a lens would disappear from bottom up. The explanation via diffraction resolution limit is wrong. However,...
- 818