# Homework Help: Life time of the hydrogen 2p state

1. Nov 28, 2008

### thesage

The problem statement
An electron going from 2p to 1s state in hydrogen sits up at the 2p for a while then jumps down.
with the given eqn
$W=\frac {4*\alpha*\omega^3}{3*c^2}*\mid r12\mid^2$
$\mid r12\mid^2=\mid<1\mid x\mid2>\mid^2+\mid<1\mid y\mid2>\mid^2+\mid<1\mid z\mid2>\mid^2$

alpha is fine structure cons, omega is the energy diff and c is speed of light

I'd imagine the life time is 1/W as the rate is per second.

The attempt at a solution
The question is okay except for the $\mid r12\mid^2$ part. Is the [itex]\mid r12\mid^2 part the expectation value of r or do i need to do the x,y,z separatly. The statement, in the question, of what [itex]\mid r12\mid^2 is confuses me.

2. Mar 26, 2011

### andresordonez

You have to do it separately, the expectation value is the matrix element of an operator between the same states, here you have two different states.