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Physics : Recent Questions and Answers (Page 112)

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

Reference frame as a $(1,1)$-tensor field $R$ with $R^2=R$

In a paper about the splitting of the space-time [for reference "THE STRUCTURE OF SPACE–TIME: RELATIVITY GROUPS" (International Journal of Geometric Methods in Modern Physics Vol. 3, No. 3 (2006)...

Asked on 08/14/2021

1 answer

Rotational dynamics about a point or an axis?

In several books and sites, it is written that torque is calculated about an axis, and angular momentum is calculated about a point. In ...

Asked on 08/14/2021 by user117913

2 answer

Commutation relation of gamma matrices

While going through the third chapter of Peskin's QFT book, I am stuck at the following proof: $$[gamma^mu, S^{rhosigma}] = (mathcal{J}^{rhosigma})^mu_{~nu} gamma^nu,$$ where, $$S^{munu} = frac{i}{4} [gamma^mu, gamma^nu]qquad;qquadqquad(mathcal{J}^{munu})_{alphabeta}...

Asked on 08/14/2021

1 answer

Infinitesimal momentum element

I understand that $d^3x$ is an infinitesimal volume element. But how do I physically make sense of $d^3p$, the momentum element?...

Asked on 08/14/2021

1 answer

Interpreting the Helmholtz equation for a time-harmonic acoustic pressure field?

An equation such as Gauss' law$$nabla cdot E(x) = frac{rho(x)}{varepsilon_0}$$is easy to interpret in physical terms. If we use the divergence theorem we have$$int_{partial...

Asked on 08/14/2021 by Ron Ronson

1 answer

How do I calculate the permeability of a magnet using the quantities on the datasheet?

I need to get a value for the magnetic permeability (μ) of a Neodymium magnet of grade $52$. On the datasheet, I have values for Remanence, Br, in Teslas,...

Asked on 08/14/2021 by Philippe Fatouros

0 answer

What is the complex dipole moment?

I have some problems with getting the complex (time dependent) dipole moments of some dipoles in a configuration. I eventually want to get the electric and magnetic fields of the...

Asked on 08/14/2021 by Djamillah

1 answer

Does a Berry phase operator exist?

The closed-path Berry phase can have measurable effects and, if I am understanding correctly, is a measurable quantity in and of itself. If that is so, is there a Hermitian...

Asked on 08/14/2021

1 answer

EMI jee metallic rod rotating in uniform perpendicular magnetic field

A metallic rod is rotating about a vertical axis through its end. For finding the EMF $E$ between the ends we simply equate $momega^2r=Eq$ then find $sqrt{-Edr}$....

Asked on 08/14/2021 by Jerry March

1 answer

Difference between covariant derivatives in general relativity and electromagnetism

There are many similarities between the gauging of a $U(1)$ symmetry to obtain the physics of electromagnetism and the gauging of diffeomorphisms to obtain the physics of general relativity....

Asked on 08/14/2021 by AnotherShruggingPhysicist

1 answer

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