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Physics : Recent Questions and Answers (Page 576)

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

Why do airplanes make a humming sound when airborne while the engines (when on the ground) make a steady sound?

I know experience-based questions are a bit tricky on this site but isn't every theory based on common experience?Every time I hear an air jetliner flying over at a...

Asked on 02/10/2021 by Deschele Schilder

2 answer

A problem with the BCS energy expectation value of an excited state

I want to calculate the energy expectation value of the following state.begin{align} |Psi_{ex}rangle = hat{c}_{-k'downarrow}^dagger hat{c}_{k''uparrow}^dagger prod_{k neq k',...

Asked on 02/10/2021 by Audrique

1 answer

Why dark matter scales in the same way as the ordinary matter?

How do we know that the energy density of dark matter in the Universe scales as that of ordinary matter in the expanding Universe? Is it a guess?...

Asked on 02/10/2021

1 answer

Electrostatics - Potential near conductor using Kelvins method of image charge

As the figure shows, I have a 2D image of a conductor seen from the front. It is located a height, h1, above a grounded plane of infinite area. The...

Asked on 02/10/2021 by Jon L

2 answer

Scaling of distance versus time in an expanding universe

As the universe expands, the (not co-moving) distance between any two points, say the distance between galaxy A and galaxy B, increases. Assume the universe behaves the same way in...

Asked on 02/10/2021 by Miss Greenbean

1 answer

About the diagonalization of non-linear (in fields) actions

Suppose we have some interacting theory with the action:$$S = int d^{D} x left(partial_mu phi partial^mu phi + V(phi)right)$$Where $V(phi)$ is a potential...

Asked on 02/10/2021

0 answer

Isothermal and Adiabatic Compression in the Carnot Cycle

I am reading about the Carnot Engine and I understood the first 2 stages (Isothermal and Adiabatic Expansion) well. In the 3rd stage where isothermal compression takes place, the surroundings...

Asked on 02/10/2021

3 answer

What do bending moments look like after coordinate frame rotation?

Suppose a 3D body had certain bending moments about the x, y, and z axes. What would the bending moments about a different coordinate system look like? In my case,...

Asked on 02/10/2021

0 answer

Meaning of components of Maxwell's stress tensor $T_{ij}$

I am learning about Maxwell's stress tensor and what I understood is that the components, say $T_{ij}$ is something like a force parallel to the $j$th-direction acting on the surface...

Asked on 02/10/2021 by Spaceman Spiff

1 answer

Determine saturation magnetization from unsaturated permeability

I need to design an electromagnet for a project, and I want it to operate close to magnetic saturation. However, I don't know the saturation magnetization of the core material....

Asked on 02/10/2021 by DELTA12

0 answer

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