Answer to Question #141735 in Quantum Mechanics for Viccy

Question

Write down expectation value of r^2.

Answer 1

The expectation value of r²:

$$\big<r^2\big>=\int^\infty_0\psi_{1s}(r)r^2\psi_{1s}(r)4\pi r^2\text{d}r=3,$$

or 3a₀².