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Physics : Recent Questions and Answers (Page 126)

Find answers to your questions about Physics or help others by answering their Physics questions.

Why is the electric field of a dielectric in a capacitor not just cancelled out outside?

As far as I know, a charged plate capacitor produces an electric field between the plates but outside the plates, the...

Asked on 08/08/2021

1 answer

Relation between the boundedness and discreteness of conjugate operators

I have two very general questions about operators in quantum mechanics. Suppose $A$ and $B$ are self-adjoint operators associated to conjugate physical quantities (e.g. position/momentum), meaning that ...

Asked on 08/08/2021

0 answer

Hermiticity of the Hamiltonian operator with probability conservation

I am following MIT lessons on quantum physics (Prof. Zwiebach): Part I, Lecture 6, at https://ocw.mit.edu/courses/physics/8-04-quantum-physics-i-spring-2016/lecture-notes/ Video lecture: https://youtu.be/Ex_fFlwZoM0 I understand that the normalized...

Asked on 08/08/2021 by franchino

1 answer

A doubt on the Topology of Einstein-Rosen Bridges (or Schwarzschild/Kruskal Wormholes)

Well, one of the "mantras" of General Relativity is:Einstein Field Equations concerns about the local geometrical structure of spacetime (the metric tensor) and tell you nothing about the fixed undelying...

Asked on 08/08/2021

1 answer

Mistake in equation 5.4 for quantum gravity baryon decay and fermion case

In the paper https://projecteuclid.org/euclid.cmp/1103922050, the equation 5.4 seems to be lacking a minus:$$left(dfrac{m_B}{m_P}right)^8dfrac{1}{m_B}sim 10^{122}yrs$$seems to be OK only if $n=-8$ (anyway, I am...

Asked on 08/08/2021

1 answer

How to prove $nablavec{V}$ is a tensor without transformation properties?

In A First Course in General Relativity, Schutz asks the reader to prove that $nabla vec{V}$ is a $(1,1)$-tensor, where $$(nablavec{V})^alpha_{ beta} equiv V^alpha_{ ...

Asked on 08/08/2021 by Doubt

1 answer

What is astrophysical fluid?

I am reading a book about astrophysical fluid dynamics, some basic fluid equations are mentioned, but is there any difference between astrophysics case and general case? Is...

Asked on 08/08/2021

1 answer

Energy conversion of electrons in cathode rays

From the principle of conservation of energy, for each electron: Electrical potential energy = Kinetic energy $$eV = frac{mv^2}{2}$$ $$v = sqrtfrac{2eV}{m}$$ where e is the charge of...

Asked on 08/08/2021 by Saitm

2 answer

Why do we call translations and time evolutions "operators" while they are not (linear) operators?

I have been reading Sakurai's Modern Quantum Mechanics and I am confused by this: A translation operator $mathscr T(delta x)$ is defined as $mathscr T(delta x) |x rangle...

Asked on 08/08/2021

1 answer

Volume of fundamental unit of discrete space and expansion of space

In this video, the following is said between 06:07 to 06:38:Now one of the interesting questions is how do you get from thequantum of space and...

Asked on 08/08/2021

2 answer

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