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Physics : Recent Questions and Answers (Page 663)

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

What is time, does it flow, and if so what defines its direction?

This is an attempt to gather together the various questions about time that have been asked on this site and provide a single set of hopefully authoritative answers. Specifically we...

Asked on 01/10/2021 by John Rennie

9 answer

How do I get the equations of motion starting from this Hamiltonian?

So I have a very complicated Hamiltonian given by: $$ H_R(psi, P_psi) = frac{-B_0 R^3}{2 pi} (2 psi - sin(2 psi) + sqrt{B_0^6 R^6 V(psi)^2 - P_psi^2} $$ where...

Asked on 01/10/2021 by Johan Hansen

1 answer

Will "water" glow at very high temperatures?

I was chatting with my kids about how incandescent lightbulbs work, clarifying that they don't so much "burn very slowly" (their original understanding) so much as they emit photons "just...

Asked on 01/10/2021 by natevw

1 answer

About variational methods, renormalization and $a$, $c$-theorems

Variational approximationVariational methods are an important technique, frequently applied for the approximation of complicated probability distributions, with the applications in statistical physics and data science. Suppose we have some complicated...

Asked on 01/10/2021 by spiridon_the_sun_rotator

0 answer

Is there a quantum analogue of the "Tennis Racket" theorem?

A non-trivial result from studying the classical mechanics of an extended object shows that rotation about an axis whose moment of inertia is between the largest and smallest moment-of-inertia axes...

Asked on 01/10/2021 by KF Gauss

2 answer

Describing a circular current loop as delta functions

It would be really nice to see how Jackson got eqn 5.33 on his example problem for finding the vector potential of a circular current loop $$J_{phi}=Isintheta'delta(costheta')frac{delta(r'-a)}{a}$$ for...

Asked on 01/10/2021

5 answer

What concepts/rules apply for multi-stage pumping of water?

For single-stage (ie one pump) water transfers calculations for pressure loss are commonly done by adding the elevation difference of the start and end of the pipeline to the friction...

Asked on 01/10/2021 by user6784

1 answer

Wavefunction of a photon

Does anyone have an explicit closed-form expression for the wavefunction of a single photon from a multipolar source propagating through free space? Any basis is acceptable as long as it...

Asked on 01/10/2021

3 answer

Finding the magnetic field by using Maxwell's laws (differential form)

According to my physics book, one can use the following laws to identity the magnetic field: div B = 0 rot B = μ0J My book also states that, given...

Asked on 01/10/2021

1 answer

What is the relation between reflectance and intensity?

I am just reviewing Fresnel's equations where Reflectance $R$ is equal to $$R=|r|^2$$ where $r$ is the complex reflection coefficient. Is there an equation that relates ...

Asked on 01/10/2021 by MathHelper123

1 answer

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