Homework Help: Quick question about hydrogen atom perturbation

1. Mar 31, 2017

davon806

1. The problem statement, all variables and given/known data

I have already solved the problem, but I don't really understand why the orbital angular momentum in the z-direction has to be taken to 0 ?

2. Relevant equations

3. The attempt at a solution
Suppose the component of orbital angular momentum in the z-direction is non-zero, that means there are extra angular momentum apart from l = 1 in the 2p state ? So when excitation occurs,it is no longer a "2p" state? Just a guess

2. Mar 31, 2017

Staff: Mentor

What is the quantum number related to the projection of angular momentum?

3. Mar 31, 2017

davon806

Oh,do you mean that the problem asks you to compute the probability from 1s -> |210> because m = 0 in the z-direction? So basically the remaining two n = 2 states have nothing to do with this question?

4. Mar 31, 2017

vela

Staff Emeritus
Check out http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/vecmod.html to see why your guess isn't correct.

The problem asked you to calculate the probability for a given final state. It could have specified a different final state and given you a different expression for the probability.