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118 views

Calulate the eigenvalues and the possible states after measurement [closed]

An observable is given by $$\sum\limits_{n= 1}^N a_n|a_n\rangle\langle a_n | $$ Here $\langle a_n |a_m\rangle = \delta_{nm}$. What are the possible measurement results corresponding to the operator A ...
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votes
1answer
319 views

Intuitively why time period of shm do not depend on displacement from mean position, ie. amplitude [duplicate]

Why simple harmonic motion time period equation is independent from displacement from mean position?
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votes
0answers
73 views

Estimate Calories Burned from Arbitrary Limb Movement

I'm looking to create a model using a reasonable physics-based approach to estimate calories burned for arbitrary movement. To keep the scope fairly limited and tractable, I am looking at the ...
0
votes
1answer
1k views

Wigner $d$-matrix for $j=1$ [closed]

In Sakurai's Modern Quantum Mechanics p.198-199, he states that for the matrix $$J_y^{(j=1)} = \frac{J_+-J_-}{2i} = \frac{\hbar}{2} \begin{pmatrix} 0 & -\sqrt{2}i & 0 \\ \sqrt{2}i & 0 &...
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votes
1answer
74 views

Is the age of the universe different for different people located at different points in the Universe? [duplicate]

From Earth we say that the age of the universe is 14.5 billion years ago because that is how far we are able to see. But since we are probably not the center of the universe, wouldn't some one many ...
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votes
2answers
78 views

If $F$ is a non-conservative force (and the unique force acting), then $δW$ is an inexact differential, but is also $dK$ an inexact differential?

Assume $\mathbf F$ is a non-conservative force and it's the unique force acting on a particle, to simplify. Elementary work done by $\mathbf F$ ($\delta W = \mathbf F \cdot \rm d \mathbf r $) is an ...
0
votes
1answer
478 views

Why do particles have spins such as $1/2$, $3/2$, $5/2$? [duplicate]

What does it mean to have 'half' spin? I have looked on Wikipedia and a few youtube videos on spin but they don't explain what it means to have $1/2$ spin. I am 18 and only starting to learning about ...
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votes
5answers
284 views

Why a body can not be accelerated to speed of light in vacuum? [duplicate]

Well i know that it needs infinite energy..but the term infinite is itself not physical so i am not satisfied with this answer ...but what would happen if we provide a constant acceleration to an ...
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1answer
483 views

What are the limitations of this form of the Navier-Stokes equation?

$$ \frac{∂u}{∂t}+u\frac{∂u}{∂x}+v\frac{∂u}{∂y}+w\frac{∂u}{∂z}=-\frac{1}{ρ}\frac{∂P}{∂x}+gx+\nu\left(\frac{∂^2u}{∂x^2}+\frac{∂^2u}{∂y^2}+\frac{∂^2u}{∂z^2}\right) $$ Why would someone use a form of ...
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votes
2answers
249 views

Confusion in understanding the concept of beats

. . .it is the combined vibration or disturbance basically having the average of the combining frequencies, but with an amplitude that varies periodically with time-one cycle of this variation ...
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2answers
85 views

Review Article on Black Holes

I have interest in doing undergrad research involving black holes, and I'm looking for review articles about it, covering all the topic, from General Relativity to the astrophysics of black holes. I ...
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1answer
67 views

Is this understanding of potential energy correct?

I am studying basic mechanics and have reached the chapter on potential energy. However I am a bit confused about the difference between potential energy and the formula for the potential energy due ...
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votes
3answers
625 views

Work done by a weight lifter

The following problem is from "The Physics Classroom": Lamar raises a loaded barbell from the floor to a position above his head with outstretched arms. Determine the work done by Lamar in lifting $...
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votes
1answer
1k views

Standard deviation as uncertainty of a single measurement

If we have made the following several measurements of the quantity x that follow a normal distribution: 86, 85, 84, 89, 85, 89, 87, 85, 82, 85 The mean is 85.7 and the standard deviation(std) is ...
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votes
1answer
49 views

Will there any modification happen?

Initially capacitor 2 is uncharged . Later it is connected with pre-charged-capacitor 1 in an open circuit . So,yet in this arrangement capacitor 1 cannot charge capacitor 2 . My question is- as no ...
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votes
2answers
595 views

Transformation of fields

In Introduction to QFT by Peskin & Schroeder, p. 18, the authors have described infinitesimal change in field as a result of infinitesimal translation as $$x^\mu\rightarrow x'^{\mu} =x^\mu-a^\mu ...
0
votes
1answer
364 views

Why this is not a perpetuum mobile [duplicate]

If we imagine a device like one shown on the picture above, why can't we say that it would work? Here is a cylinder somehow placed in the fluid by one of his sides (one in the box). Due to additional ...
0
votes
1answer
336 views

What are the Electric and Magnetic Properties of Aluminum Oxynitride?

Is Transparent Aluminum (Aluminum Oxynitride) a good conductor of electricity? Also, is it attracted by a magnet?
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2answers
125 views

Understanding entropy production

I found this concept of entropy production in wikipedia. Mainly I am trying to figure out the formula the Clausius formula for entropy production. What exactly are the terms involved? For what ...
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votes
0answers
59 views

Generating very large area gamma rays by other ways other than large accelerators

According to this link https://apps.dtic.mil/dtic/tr/fulltext/u2/a351472.pdf, HERMES III at Sandia National Labs can generate very large area gamma rays by converting the electron beam into ...
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votes
2answers
116 views

Wave function collapse and a general wave function

Action of an operator on a state vector collapses the wave function to any of the eigenstate of that operator , So we get resulting state of the system as some base ket. But mathematically action of ...
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votes
1answer
261 views

Can we generate electric current by injecting electrons into a copper panel

Suppose I take a vacuum tube and accelerate electrons in it by electric fields then collide it on a copper plate. Will the electrons then go inside it and generate an electric current by putting a ...
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votes
2answers
6k views

What does grounding a plate mean happens to the charge?

In the context of image charges. Let say I have a very large grounded/earthed plate. If initially the total charge on the plate is 0 then we place a positive point charge, $Q$ just above its surface (...
0
votes
1answer
191 views

Momentum of wave function with sum of cosines

I am struggling with question about possible outcomes of momentum measurement and their probability. I know I can calculate it with momentum operator, but a wavefunction is of form $$\psi (x)=3\cos\...
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votes
1answer
85 views

Is mass moment of inertia measured to the point of interest or the entire object?

I'm trying to calculate the amount of kinetic energy that a point of a rectangle of wood will have after it swings and hits something. I have the following diagram: where there is a rectangle ...
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votes
1answer
71 views

Radial Schrödinger equation of a scattering in two dimentions

The scattering, in two dimensions, of a particle of mass $m$ by a central potential $U(r)$. The hamiltonian of the system is $H= p^2/2m + U(r)$. Then the radial wave function $ϕ(r)$ is obtained as a ...
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votes
3answers
129 views

What time dilation effect would occur when two objects near the speed of light approach each other? [closed]

What time dilation effect would occur when two objects would approach each other at e.g. 90% the speed of light? For each of the objects the other object appears to be moving at 180% the speed of ...
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2answers
2k views

Can electromagnetic fields interact with each other? [closed]

For example - if one were to generate an electromagnetic field using super-cooled magnets, and the magnets were shut off, is it possible for another field to interact with the collapsing one and ...
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votes
1answer
2k views

Calculating the first cosmic velocity / velocity for a circular orbit

Today in class we calculated first cosmic velocity using this equation $$G\frac{mM}{(R+h)^2}=\frac{mV^2}{R+h},$$ where $m$ = mass of the body, $M$ = mass of the Earth, $R$ = radius of the Earth, $h$ = ...
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votes
1answer
76 views

Are there other theories than gravitational attraction taken into account as a reason for the extreme accumulation of matter in the universe?

This question is about how small the interstellar density is (less than 1 atom per cubic centimeter). But although the interstellar density is very low, matter tends to extremely aggregate in certain ...
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2answers
1k views

Differences between elastic moduli

Is it true that in materials like aluminum and copper, the correct order of elastic moduli, in terms of value are: Bulk < Young's < shear modulii If this is correct, why is this the case?
0
votes
1answer
150 views

(2+1)-d Unitary irreducible representations of the Poincare group

I am currently working through this paper on relativistic field theories in three dimensions. I have come to terms with the classification of Unitary irreducible representations (UIR's) given. The ...
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votes
1answer
380 views

Ignoring spin, what is its orbital magnetic moment of an electron in a hydrogen atom in the 2p orbital?

I know that a magnetic dipole moment is given by $$\mu=\frac e{2m}I$$ and that the angular momentum is $$\frac {m_jh}{2\pi}.$$ However, I have also seen that angular momentum $I$ is given by $$I=\frac ...
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votes
1answer
912 views

Transmission of Gaussian Beam Through Graded-Index Slab

The $ABCD$ matrix of a glass graded-index slab with refractive index $n(y)=n_0(1-\frac{1}{2}\alpha^{2}y^{2})$ and length $d$ is $A=\cos(\alpha d)$, $B=\frac{1}{\alpha}\sin(\alpha d)$, $C=-\alpha \sin(\...
0
votes
1answer
4k views

Relativistic Kinematics - 2-Body Particle Decay

Consider the scenario where a particle of mass $M$ decays into two lighter particles of mass $m_1$ and $m_2.$ In the center of mass frame (i.e. $\mathbf{p}_1$ and $\mathbf{p}_2$, the momenta of the ...
0
votes
1answer
641 views

Lagrangian for electron radiating a photon

I know the electron-photon interaction Lagrangian from QED: ($-ie\bar{\Psi}\gamma^{\mu}A_{\mu}\Psi$). However, this interaction seems to describe the interaction of electron and positron with a photon ...
0
votes
1answer
65 views

How do electrons exit LEDs? Aren't they in the valence energy state?

If a conducting electron reduces to the valence band in an LED, where does it get the energy to go back to the conductance band upon leaving the diode so current can flow? I'm confused as to how ...
0
votes
2answers
2k views

what is the result of change in gravitational flux?

As a change in magnetic flux results in induced EMF (electromotive force) likewise what is the result of a change in gravitational flux? UPDATE: Gravitational flux according to me has only ...
0
votes
2answers
1k views

Classical particle in box - Force on wall [closed]

I'm trying to calculate the force exerted on the wall by a particle contained in a 1 dimensional box of length $L$ using classical physics. The hint is that the change in momentum is given by $$\...
0
votes
1answer
220 views

Methods of detecting gravitino DM and possible implications for theories of everything

Let me summarize my thoughts about topics in theoretical physics: Theory of everything: The theory of everything aims to unite all the four forces of nature into one single elegant equation. ...
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votes
1answer
270 views

Quantum mechanical tunneling

Keeping extraneous ideas and postulates to a minimum, How can we explain the process of quantum-mechanical tunneling?
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3answers
128 views

Can anyone help me in these questions (related to Work Done) [closed]

Can work done by Kinetic Friction on an object be positive? Zero? Can Static Friction do Non-zero work on an object? Can Normal Force do Non-zero work on an object?
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3answers
2k views

Why is charge $= nALe$?

Sorry if this question is a bit broad but I can't find any info on this by just searching. The equation $q = neAL$ where $L$ is the length of a conductor, $A$ is the area of cross section, $n$ is the ...
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votes
2answers
120 views

Since nucleons are not elementary particles more, how we call nucleons and electrons together now? [closed]

In the time before the discovery of quarks the nucleon particle proton and neutron together with electrons were called elementary particles. It's a little bit boring to have only the possibility to ...
0
votes
2answers
261 views

How to ascertain that the Rayleigh-Ritz variational method gives the exact value of the ground state energy?

So the Rayleigh-Ritz variational method can be used to calculate the ground state energy of a quantum system. If $\phi(x)$ is a suitable (square integrable) and normalised function of the coordinates ...
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votes
1answer
38 views

Does the decay energy of a beta decaying isotope become lower as the half life becomes greater (or vice versa)?

In other words, does half life have a correlation with decay energy of a beta particle?
0
votes
3answers
86 views

Why does striking two balls of equal mass and equal magnitude of velocity turn the system to rest?

In the answer by Ron Maimon in this stack post, he writes: if you smack two identical clay balls of mass $m$ moving with velocity $v$ head-on into each other, both balls stop, by symmetry. The result ...
0
votes
1answer
68 views

When you introduce excess charge into an insulator the charge stays still. Why is this?

When you add charge to an insulator the electrons stay in the same place whereas in a conductor they spread apart. Why is this? What force is making the excess charge stay in one place in an insulator?...
0
votes
1answer
726 views

Is Volumetric flow rate constant?

I'm working on a project and I need to know something. My project is about a toy CD hover craft. It's a balloon, connected to a CD via a tube or a pipe, like this: I want to know that is the ...
0
votes
3answers
77 views

Explaining rest electron magnetic field through Special Relativity

I was reading this post. It says that the electron produces a magnetic field due to its internal magnetic dipole which is given by $$ {\boldsymbol \mu}= \frac{eg}{2m} {\bf S} $$ In Purcell's book, he ...

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