# [SOLVED] Virial Theorem

by ultimateguy
Tags: solved, theorem, virial
 P: 126 1. The problem statement, all variables and given/known data A particle has a potential $$\lambda X^n$$ and Hamiltonian $$H = \frac{P^2}{2m} + V(x)$$ Knowing that the commutator of H and XP is $$i\hbar(n\lambda X^n - \frac{P^2}{m})$$, find the average values and and verify that they satisfy: $$2=n$$ 2. Relevant equations 3. The attempt at a solution The question asked to calculate the commutator and that is what I found, but I'm lost as to how to get the average values and proove the inequality.
 PF Patron Sci Advisor Emeritus P: 11,137 The question doesn't actually ask you to calculate the commutator; it gives you the value of the commutator (though with a sign error; it should read ...-P^2/m). The next step is to recall what the commutator of any operator with the Hamiltonian gives you (Hint: Heisenberg EoM). After that you just have to take the time average on both sides, and take the limit of loooong times.
 P: 126 The question asked to calculate the [H, XP] commutator, I just didn't write it because I already found it and wanted to save time. I'm not sure I understand the hint.
PF Patron
For an operator A, that is not explicitly time-dependent, $(i\hbar) dA/dt$ is equal to a commutator. Does that help jog your memory?