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Physics : Recent Questions and Answers (Page 262)

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

Why don't evanescent waves give rise to electromagnetic waves?

I'm reading about evanescent waves for the first time. I understand that even thought no electromagnetic wave is transmitted across the boundary, an electric field is transmitted which decays exponentially...

Asked on 06/14/2021

3 answer

What are the cross-sections for neutral-impact excitation?

One way for bound electrons in an atom (e.g. neutral helium) to transition to a higher energy level is via electron-impact excitation (i.e. collisions with free electrons). Accordingly, one can...

Asked on 06/14/2021

0 answer

How to solve this problem while taking torques about the lower end of the ladder?

This is a problem from my introductory physics textbook:The ladder shown in the figure has negligible mass and rests on a frictionless floor. The crossbar connects the two legs of...

Asked on 06/14/2021 by Ray Bradbury

2 answer

Does the contact angle of a drop depend theoretically on the size of the drop?

According to Wikipedia, contact angle depends on the hydrophobicity of the surface and on thermodynamic equilibrium. But how does it in theory depend on the drop size? In...

Asked on 06/14/2021

1 answer

Does a planar object balance on a unique point?

Consider a horizontal planar convex 2D object (say lying on x-y plane) with uniform density. Under constant gravitational force (say in -z direction), does it always balance on a...

Asked on 06/14/2021

4 answer

How is this Yukawa coupling term invariant?

I have the seen the following term used to describe Yukawa coupling for the lepton and Higgs field: $$ epsilon_{ij}phi^{i}bar{e}_{R}f_{L}^{j} $$ Under $SU(2) otimes U(1)$ and so expected...

Asked on 06/14/2021 by CauchySchwarzMan

1 answer

Solution to Dirac equation

We take the solution of Dirac equation as 4 component wave function (Dirac Spinor). But how do we know that it can't be a square or rectangular matrix like 4x2...

Asked on 06/14/2021 by Siddharth Jain

1 answer

Driving a quantum system

I don't understand the mathematical form of an external driving force on a quantum system. For example, say we were driving a quantum harmonic oscillator. You would have the Hamiltonian...

Asked on 06/14/2021

0 answer

Can we use Bosonization to study models without $U(1)$ symmetry?

When studying lattice models using bosonization, we expect the charge is preserved so that the elementary excitation is particle-hole like bosonic degrees of freedom. How about models without $U(1)$...

Asked on 06/14/2021

0 answer

Why is pressure $rho g R$ at all points on the base of this upside-down container

The container is inverted and filled with water through a hole on top and it is said the pressure on...

Asked on 06/14/2021

2 answer

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