Introduction to Quantum Mechanics · Problem 6.21

Symmetries and Conservation Laws — David J. Griffiths

Physics — Quantum Mechanics · hydrogen_expectation_value

Problem

For an electron in the hydrogen state

\psi = \frac{1}{\sqrt{2}}\left(\psi_{211} + \psi_{21-1}\right),

find

\langle r \rangle

after first expressing it in terms of a single reduced matrix element.