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Physics : Recent Questions and Answers (Page 255)

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

Why are there $3N - 3$ optical branches for a system in 3-Dimensions with $N$ different atoms per unit cell?

I am specifically referring to when we can approximate the atoms to be in a chain and they interact via harmonic potentials, for instance, if $N = 2$, we have...

Asked on 06/17/2021 by user45815

1 answer

Killing Tensor of Friedman-Robertson-Walker Metric

I would like help showing that the tensor, $$K_{munu}=a^2(g_{munu}+u_mu u_nu),$$ where $u^mu =(1,0,0,0)$, is a Killing tensor of the spatially flat FRW metric, $$ds^2=-dt^2+a(t)^2left(dr^2+dOmega^2right).$$ Specifically it...

Asked on 06/17/2021 by user1508915

1 answer

Is the particle-hole transform rigorous in infinite-dims?

$DeclareMathOperator{tr}{tr}$Let me only consider fermions, i.e., fermionic Fock space $mathscr{F}$ of a single-particle Hilbert space $mathscr{H}$. Let us assume that $dim mathscr{H}=aleph_0$ (infinitely countable). Based on...

Asked on 06/17/2021

0 answer

Magnetic Field Strength in Plane of and Outside Current Loop

I am trying to find a relationship between the magnitude of the magnetic field at distance $x$ in the plane of a wire loop with radius $R$, $n$ turns and...

Asked on 06/17/2021 by unknown-placeholder

1 answer

Is there still no known origin of the law of inertia?

To quote Feynman at about the 21 minute mark of the first Messenger Lecture on The Character of Physical Law,...that the motion to keep it going in a...

Asked on 06/17/2021

10 answer

Can an electric field align water molecules?

Water is a polar molecule, which means it has an uneven charge distribution. How much of an electric field strength would it take to align all, or most, of the...

Asked on 06/17/2021

1 answer

Experimental $g^{(2)}$ measurement

I'm in need to find a paper/book that discusses how to obtain the $g^{(2)}$ correlation of a certain emitter when using an Hanbury Brown...

Asked on 06/17/2021

1 answer

Group velocity in solid state physics force equation

When reading about electron holes here https://en.wikipedia.org/wiki/Effective_mass_(solid-state_physics), the group velocity is introduced as the reciprocal space gradient of the dispersion relation. The group velocity is then used...

Asked on 06/17/2021

1 answer

Why do we care about indistinguishability?

I am reading material related to statistical physics, and I am having a problem understanding why we care about the notions of distinguishably and indistinguishability. I have found What...

Asked on 06/17/2021 by M. Whyte

2 answer

Can the interstellar wind / radiation make water undrinkable

I was watching a video on the dangers of stellar travel especially interstellar. The video was discussing the interstellar wind and the damage it could do to the crew....

Asked on 06/17/2021

1 answer

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