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Physics : Recent Questions and Answers (Page 719)

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

Energy-momentum tensor for a Lagrangian with no explicit spatial dependence

Suppose I have a Lagrangian $mathcal{L} = mathcal{L}(phi, partial_mu phi)$ for a (let's say) real scalar field with no explicit temporal or spatial dependence. Then I believe the usual...

Asked on 12/21/2020

0 answer

Fluctuation dissipation theorems in dynamic processes: a comparison

I do not understand what the first and the second fluctuation- dissipation theorems physically represent and what are the differences between the first and the second on the physical side....

Asked on 12/21/2020 by Hub One

0 answer

Estimating partition function using Montecarlo methods

While working on a completely unrelated quantum computing problem, I ran into a quantity that can be mapped to a partition function of spins on a triangular lattice. It is...

Asked on 12/21/2020 by Angelo Brillante Romeo

1 answer

Electrostatics and electric field inside conductor

I have tried for a while finding an answer to this question. Similar ones have been explained earlier by using Gauss law. However I am wondering about the physical change...

Asked on 12/21/2020 by Gjert

2 answer

Landau gauge momentum conservation question

I'm having an issue understanding why $hat{P}_x$ commutes with the Hamiltonian in the Landau gauge ($A_x=-Bhat{Y}, A_y=0$) in two dimensions. I've been finding elsewhere online the hand-wavey argument...

Asked on 12/21/2020 by Ethan Mullen

0 answer

Does the Ricci tensor actually change volume of a body in reality?

I have learned about the Ricci tensor and I was wondering if it actually changes volume in real-life physics.The question I know the Ricci tensor is a mathematical object...

Asked on 12/21/2020 by Tachyon

3 answer

What should be the direction of motion of a conductor in a magnetic field to produce motional emf?

Here's the textbook question: Twelve wires of equal length 'l' are connected to form a skeleton cube which moves with constant velocity v perpendicular to the magnetic field B. What...

Asked on 12/21/2020 by Swami

3 answer

Cosmological constant (CC) vs vacuum energy density (VED)?

How are the two different? I know that CC has negative pressure and opposes gravity. But what about VED? Is VED supposed to have positive pressure and cause gravity too?...

Asked on 12/21/2020

0 answer

Is Thibado’s Graphene Brownian Capacitor Charger Perpetual Motion of the Second Kind?

In Fluctuation-induced current from freestanding graphene (peer-reviewed version on Phys. Rev. E, note: behind a paywall) Thiabado, et al, report the extraction of work...

Asked on 12/21/2020 by James Bowery

2 answer

Energy transfer involved in lowering a weight

Suppose I lift a weight of 1kg through 1metre, say from the floor to my waist height. The Potential Energy or work done against gravity is: PE=mgh= 1kg x 9.81m/s^2...

Asked on 12/21/2020 by Ludo

2 answer

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