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I'm trying to prove that for a particle in a potential V(r), the rate of change of the expectation value of the orbital angular momentum L is equal to the expectation value of the torque:

[tex]

\frac{d}{dt}<L> = <N>

[/tex]

where

[tex] N = r \times (-\bigtriangledown{V}) [/tex]

Basically, I'm having problems calculating the commutor of the Hamiltonian and the angular momentum operator, as

[tex]

\frac{d}{dt}<L> = \frac{i}{\hbar}<[H,L]> + <\frac{\partial{L}}{\partial{t}}>

[/tex]

Any hints on how I can calculate this?

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# Rotational Analog to Ehrenfest's Theorem

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