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1answer
72 views

Why can one equate the the zeroth order coefficient with the initial state in time-dependent perturbation theory in quantum mechanics?

Setup In the typical treatment of time-dependent perturbation theory in quantum mechanics, one arrives at the set of equations $$ i \dot{a}^{(r + 1)}_m(t) = \sum_n \langle m |H_1(t)|n \rangle e^{i ...
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1answer
608 views

Applications of the particle in a box and the finite square well

What are some "real" world applications of the particle in a box (PIB) and the finite square well (FSW) which are discussed in an intro quantum mechanics class? For instance, I know that the PIB can ...
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1answer
200 views

Why does an ice rink use a primary and secondary coolant?

A normal refrigeration cycle uses one coolant, so why does vapor compression cycle of an ice rink you a primary coolant and a secondary coolant?
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1answer
179 views

How to uncurve a black hole

How can you uncurve a black hole and thereby get at the stuff inside? The Big Rip as dark energy reaches its zenith at the end of the universe. If curvature is a quantum field that is a ...
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2answers
265 views

Quantum Mechanics- Antenna emitting electromagnetic radiation

Radio signals are being transmitted in a frequency of $ 8.4 \times 10^9 s^{-1} $ and being received by an antenne that is capable of receiveing power of $ 4 \times 10^{-21} watt $ ($ 1 watt = 1 J ...
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2answers
356 views

State-dependent diffusions: Fick's law vs. Fokker-Planck's, which and why?

Consider a "state-dependent diffusion": a diffusion process for which the diffusion coefficient $D(x)$ depends on the (stochastic) state $x$ of the system. (An example is provided by the diffusion of ...
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2answers
122 views

Has there been any serious work in how the world would look if basic physical laws were changed?

Has there been any serious work in investigating how the world would look if certain basic physical laws were changed? Like if gravity or electromagnetism laws were changed to have different ...
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1answer
173 views

Loopy lightning

What causes lightning to follow the path it does ? picture from BBC news: http://news.bbcimg.co.uk/media/images/62891000/jpg/_62891901_untitled-1copy.jpg main page: ...
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1answer
85 views

Waves travelling with water flow

Suppose I use a tool to create a circular wave in the river. If there are two fish swimming 1m from the source (2m from one another), they will both feel the wave at the same time. What will happen ...
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1answer
199 views

Friction between atoms in spring

if i doing experiment on spring-mass system in vaccum,if i pull the to some extent (within elastic limit of spring) & let it go,will the system oscillate indefinitely? (neglect contact frictions ...
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1answer
131 views

Ratio of the isospin of the photon

as known the photon can have an isospin of 0 and 1. However, what is the ratio of both for an virtual photon (in e+e- annihilations)? Next to an 1^-- resonance like J/Psi or Psi' it should be 1 in ...
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2answers
166 views

Is it really to solve problem below by using, in the main, Gauss law?

There is an infinite cylinder surface which uniformly charged along and has a surface charge density, which can be represented as $$ \sigma = \sigma_{0}cos(\varphi ), $$ where $\varphi$ - polar angle ...
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1answer
312 views

Problem book in Quantum mechanics with emphasis on physical(ly relevant) problems [duplicate]

I am a second year undergraduate and studying quantum mechanics from sakurai's 'Modern Quantum Mechanics'. Is it a good idea to solve problems from sakurai, which are mostly mathematical in nature? I ...
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1answer
137 views

Relating theta_QCD to neutron EDM

How do I relate the topological $\theta_\text{QCD}$ parameter to the electric dipole moment (EDM) of the neutron? I am very familiar with chiral perturbation theory. I just need to know how to take ...
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1answer
193 views

Calculation of Commutation in constraint analysis

During analysis the constraint from a theory, suppose my canonical Hamiltonian is $$H_c=P^A\dot{A}+P^B\dot{B}-L$$ where $P^A=\frac{\partial L}{\partial \dot A}$ and $P^B=\frac{\partial L}{\partial ...
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1answer
342 views

Symbol for dashpot/damper (in a harmonic oscillator)

In diagrams that contain the dashpot symbol, sometimes the mass is attached to the "interior" end of the dashpot, other times the mass is attached to the "base" end. For example, consider the ...
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1answer
101 views

Where can I find hamiltonians + lagrangians?

Where would you say I can start learning about Hamiltonians, Lagrangians ... Jacobians? and the like? I was trying to read Ibach and Luth - Solid State Physics, and suddenly (suddenly a Hamiltonian ...
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2answers
351 views

How can a non-conservative field be a scalar multiple of a conservative field?

Okay so I was reading this from University Physics by Freeman and Young and on the topic of inductors as circuit element, they wrote that $\mathbf{E_c} + \mathbf{E_n} = 0$ which makes no sense to me ...
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1answer
193 views

Aharonov-Bohm vs de Witt

dewitt claimed in his paper Bryce S. DeWitt. Quantum theory without electromagnetic potentials, Phys. Rev. 125 no. 6 (1962), pp. 2189-2191, DOI: 10.1103/PhysRev.125.2189, that the discovery ...
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2answers
115 views

When do the von Neumann projections occur and what causes them?

(Transferred as a separate question from comments in Scott Aaronson’s gravitational decoherence question) Reversing gravitational decoherence The modern answer seems to be that they never occur, ...
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1answer
247 views

Calculating the direction of the force acting on a source of magnetic field

I do not know how to calculate the direction, or unit vector of the force that appear between two magnetic field sources. For example, let's assume I mean a current-carrying-wire by 'source of ...
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1answer
160 views

polarization and frequency of a single photon

I believe that we can take a single photon state as a tensor product of a frequency Hilbert space (infinite dimension) and a polarization Hilbert space (dim 2). Does this mean we can measure the ...
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2answers
138 views

Can double entanglement preserve correlations?

We have 2 EPR experiments running in parallel, with Alice having one leg of each (a1,a2) and Bob the other leg of each (b1,b2). Thus (a1,b1) are anticorrelated, as are (a2,b2). Thus also (a1,a2) are ...
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2answers
4k views

The most efficient Fan Blade Design [closed]

What could be the most efficient fan blade design? There are three main factors for a good fan: one is speed at which air is circulated; second,the volume of air it can circulate; and the third is ...
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2answers
277 views

How the spectrum of the hydrogen atom is checked/detected experimentally?

When solving the hydrogen atom, as a 2 body problem, we have the motion of the center of mass and the motion relative to the center of mass. The well known energy spectrum, $E_n$, that goes like ...
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2answers
244 views

Why does heterodyne laser Doppler vibrometry require a modulating frequency shift?

On the wikipedia article (and other texts such as Optical Inspections of Microsystems) for laser Doppler vibrometry, it states that a modulating frequency must be added such that the detector can ...
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1answer
80 views

Are there dedicated instruments to measurethe viscosity of shear thinning liquids?

Googling around for ways to measure the viscosities of shear thinning liquids, it seems to me that most of the time viscometers are used at different settings to measure different apparent ...
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1answer
444 views

What does 'energy dissipation' in the description of the Kolmogorov Microscales in fluid dynamics mean?

I've asked about microscales before, and thinking more about the problem turned up more basic questions. Consider the length scale of a microscale: $$ \eta = ...
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1answer
145 views

What are the characteristics of a quadripole circuit element?

I'm reading Music, Physics and Engineering (H. Olson 1967), and contains models of musical instruments as electric circuits, i.e. uses the analogies between electrical circuits and mechanical ...
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1answer
99 views

What is the difference between “at all times” and “at any particular time”?

Morrison writes in "Morrison, Michael A. : Understanding quantum physics : a user's manual" $ |\Psi(x,t)|^2 \xrightarrow[x\rightarrow\pm \infty ]{} 0$ at all times t [bound state] $ ...
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1answer
701 views

What is physics of a normal jump?

What is the physics behind a normal human jump ? when a normal human wants to jump. First, some energy is stored in their thighs and The elastic tendons Just like a spring. In mechanics and ...
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1answer
189 views

On the Discretization of Energy Levels

We consider a system of "n" particles whose total energy E and net momentum $\vec{P}$ are fixed are fixed.There no net force on the system(assumed) $$\Sigma \epsilon_i= E$$ ...
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1answer
289 views

What is discontinuity in Vector Fields

I am reading David J. Griffiths and have a problem understanding the concept of discontinuity for E-field. The E-field has apparently to components. (How does he decompose the vector field into the ...
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3answers
118 views

Estimate quarter mile time

I need to estimate a drag race quarter mile time given the car's weight, bhp and preferably the drive (FWD, RWD, 4WD). I know $v(t) = ds/dt$ and $a(t) = dv/dt = d^2s/dt^2$, but how can I get the ...
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1answer
185 views

What is theory of Free Energy Perturbation? How is it applicable to chemical science?

What is theory behind free energy perturbation? Is it way too difficult to understand? Can someone explain it in simple terms.
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1answer
527 views

Calculating capacitance of integral PCB components

I posted this question originally with Electrical Engineering Stack Exchange but nobody seems to know the answer. So I thought a physicist might find the question more approachable. Formulas for ...
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2answers
350 views

Where does the “borrowed energy” come from in Alpha decay?

I was also thinking about the uncertainty principle in regards with energy & time. The question of something like: Alpha tunneling out of the nucleus is where this can be invoked, but having an ...
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3answers
282 views

Why is the tunnel effect of solid matter not observable in macroscopic objects?

Assume I place a tea cup on a table (say, about a centimetre thick). Quantum mechanics tells us that the wave function for the nuclei and electrons of the cup is not zero below the table (while being ...
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1answer
73 views

At what rate does radiation exposure occur at high-c speeds?

If a future astronaut travelled to Alpha Centauri at a significant percentage of light-speed? Apart from increased blue shifted radiation from their direction of travel - how would they experience ...
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2answers
486 views

Proof of charge existence on a grounded conductor

A question regarding the existence of charge on grounded conductors is confusing me. Could there be charge on a grounded conductor? How does this not contradict Gauss's Law? Since every conductor ...
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1answer
141 views

what is wrong with the following argument about stokes law in compact universes?

I want to understand what is wrong with the following argument: in a topologically compact spacetime, a closed 3D boundary separates the spacetime in two connected components, because of this ...
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1answer
402 views

Non-conservative Electric Field

I was watching this video from Walter Lewin and while watching these two videos, I noticed there is a "contradiction" in what he is doing. All links direct you exactly to where he begins, so you don't ...
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2answers
393 views

Maxwell-Boltzmann distribution and total energy per unit volume

We know that $$n(E) ~=~ \frac {2 \pi (N/V)}{(\pi k_B T)^{3/2}} E^{1/2} e^{-E/(k_B T)} dE,$$ where $V$ is total volume. If then, how do we derive total energy per unit volume from this equation?
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1answer
59 views

References for nuclear masses, mass deficits, decay rates and modes

Where can I find the base data for computing the energy release of nuclear decays and the spectra of the decay products? My immediate need is to find the energy release by the beta decay of Thorium ...
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1answer
330 views

Multi-component mixture phase equilibrium criteria

For a pure species, the equlibrium between liquid phase and vapour phase is given by the equality of molar Gibbs energy in both phase: $$\underline{G}^l=\underline{G}^v$$ Where $\underline{G}$ with ...
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1answer
526 views

Suvat equations in reverse direction

This might be a basic question, but please help me out. I have an object traveling in the positive direction with a velocity $v$ and I wish to apply a constant acceleration so that the final velocity ...
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1answer
121 views

Matter wave of multiple particles of different types

I am slightly getting confused on the following issue: When performing double-slit experiment of electrons, a screen allows the matter waves to be detected as particles. And as we all know that ...
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1answer
117 views

Motion of a plank hinged about a point

There is a plank hinged about a point O. At the free end of the plank a small impulse is given. Will the plank perform pure rotation or both rotation and translation?
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1answer
234 views

Lepton masses in the Standard Model

Some simple questions regarding leptonic masses in the Standard Model (SM): Why there is not an explicit mass term in addition to the effective mass term that arises from the Yukawa terms after ...
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2answers
113 views

Looking for the curve traced by a moving bicycle when its steering bar is fully rotated

I am looking for a curve traced by a moving bicycle when its steering bar is fully rotated either clockwise or anti-clockwise. How to model it mathematically? Is the curve a circle? My attempt is ...

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