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Physics : Recent Questions and Answers (Page 704)

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

Spin part of the angular momentum from the Lagrangian

For fermions of spin $1/2$ the angular momentum has following form:$$mathcal{J}_z = int d^{3}x psi^{dagger} (x) left[i(- x partial_y + y partial_x) + isigma^{xy} right]...

Asked on 12/27/2020

3 answer

Exceptions for Plane Waves Rules

Let's consider plane waves propagating along $z$ direction, namely wave of this form: $vec E(ctpm z)$,$vec B(ct pm z)$.On my book there is a derivation that...

Asked on 12/27/2020 by SimoBartz

0 answer

Einstein's Derivation of Lorentz transformations

I have been reading the derivation of Lorentz transformations in the appendix of relativity:the special and general theory by Einstein and am stuck in the following spot:He states...

Asked on 12/27/2020 by A.G

1 answer

Energy of a Hamiltonian that is the sum of commuting Hamiltonians

Suppose that $$H=sum _i H_iquadtextrm{with}quad [H_i,H_j]=0 quadtextrm{for} quad jneq i$$ Let $psi_i$ be a solution to $H_i$ so that $$H_ipsi_i=E_ipsi_i$$Does this always imply that the solution...

Asked on 12/27/2020 by user224659

3 answer

Effect of motion on ball in a moving cart

I know that in case of cart moving with an acceleration we are supposed to apply the concept of pseudo acceleration to judge the motion of ball in frame of...

Asked on 12/27/2020 by Saniya

1 answer

How can a classical phase space be unquantizable?

On page 2 of the paper "2 + 1 dimensional gravity as an exactly soluble system" Witten claims that:Depending on its topology, a finite-dimensionalphase space might be unquantizable,How a...

Asked on 12/27/2020 by Arian

1 answer

Indices in Dirac's spinorial representation

The other day in class we derived Dirac's equation and talked a little about its relativistic covariance. In particular, we said that the electronic wavefunction $psi(x)$ transforms as ...

Asked on 12/27/2020

0 answer

Solutions of the Harmonic Oscillator are *not* always a Combination of Separable Solutions?

Are there solutions of the Schrödinger equation that are not a linear combination of separable solutions and how do we find them? In Griffiths, Quantum, Prob. 2.49, there is a...

Asked on 12/27/2020

1 answer

Obtaining Inverse configuration space metric $M^{AB}$ in canonical gravity

I am considering phase space of configuration variables in general scalar tensor theory $(q^A=(h_{ab},phi))$, characterised by the metric: $ M_{AB}=frac{sqrt{h}}{N}begin{pmatrix} frac{U(phi)}{2}G^{abcd}&-U'(phi)h^{ab}-U'(phi)h^{cd}&G(phi)end{pmatrix}; $ prime denotes derivative w.r.t...

Asked on 12/27/2020

0 answer

Is it Possible to Directly Measure Energy?

Would it be possible to measure energy directly in joules instead of measuring what effect energy has on something? Say for example you have a car of known weight traveling...

Asked on 12/27/2020 by ballpoint

2 answer

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