# Expectation value of 1s state of hydrogen driving me absolutely nuts

My question says:

"Evaluate the expectation value <1/r> of the 1s state of hydrogen. How does this result compare to the result found using the Bohr theory?"

Firstly, I have been told that <1/r> does not mean <1/r> but rather that it means 1/<r>. Having made it this far I now do the 1/<r> and get about 12 times the bohr radius which is obviously wrong. Apparently the answer is 3/2 the bohr radius.
But also, I thought that doing <r> was supposed to give you 3/2 bohr radius, so what is this 1/<r> for?
Basically, what the hell is going on, in simple, clear terms???
Thank you for any help,
Ben

## Answers and Replies

Meir Achuz
Science Advisor
Homework Helper
Gold Member
1/<r> is wrong. It should be <1/r>.