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Physics : Recent Questions and Answers (Page 209)

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

Ricci scalar for FRW metric with lapse function

I need the Ricci scalar for the FRW metric with a general lapse function $N$:$$ds^2=-N^2(t) dt^2+a^2(t)left [frac{dr^2}{1-kr^2}+r^2(dtheta^2+sin^2theta dphi^2)right]$$Could someone put this into Mathematica as I don't...

Asked on 07/05/2021

0 answer

Why is the first derivative of the time-dependent Schrödinger equation continuous? Where does it come from?

I was taught in first year physics that the first derivative of the time-dependent Schrödinger equation had to be continuous. However I was never taught (or at least I don't...

Asked on 07/05/2021

1 answer

Electric field lines fall within a circle?

I was going through the method of images using 2 positive point charges placed along a line perpendicular to an infinite grounded conducting plate. I had found the surface charge...

Asked on 07/05/2021

1 answer

Does spin precession stop immediately after leaving Stern-Gerlach apparatus and split into the orthogonal direction of precession?

A small concept I'm a tiny bit confused about. Sakurai in the introduction to quantum mech introduces the Stern Gerlach experiment. According to his discussion, an $S_{x}+$ particle that...

Asked on 07/05/2021

2 answer

Why do physicists assume that dark matter is weakly interacting?

IceCube, XENON, etc, keep yielding negative results. If dark matter exists, it doesn't interact with baryonic matter at the energy ranges they can detect. The response is to build even...

Asked on 07/05/2021 by Foo Bar

3 answer

Why do higher frequencies tend to have a smaller amplitude than low frequencies?

Complex waves found in nature tend to have downward sloping frequency distribution. This isn't to say the fundamental always has the highest level but the general trend is that higher...

Asked on 07/05/2021 by john_the_fisherman

1 answer

Electromagnetic current operator using Feynman rules

In the calculus of the electron anomalous magnetic moment some text books usually calculates the forms factors from $Gamma_{mu}$ in the expression bellow $$left<p',s'|J^{em}|p,sright> = frac{e^{iq.x}}{sqrt{2EV}sqrt{2E'V}}bar{u}(p')Gamma_{mu}u(p)$$ and...

Asked on 07/05/2021

1 answer

Why are cooling towers at nuclear power plants shaped the way they are?

The iconic cooling towers at most nuclear power plants are shaped like hyperboloids. Wikipedia mentions that this is because the wide base promotes thin film evaporation and...

Asked on 07/05/2021 by templatetypedef

6 answer

Weyl spinor being on-mass or off-mass shell

Is there a way to know whether a two component Weyl spinor is on-mass or off-mass shell?...

Asked on 07/05/2021

0 answer

Quadratic Casimir of Higher dimensional representations

I am trying to find the quadratic Casimir of a 45 dimensional representation of ${rm SU}(5)$. However, in many references, the dimension of the representation of ${rm SU}(N)$...

Asked on 07/05/2021

2 answer

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