# Hydrogen in forbidden region

Any region of space in which the kinetic energy T of a particle would become negative is forbidden for classical motion. For a hydrogen atom in the ground state:
(a) find the classically forbidden region
(b) using the ground-state wave function $$\psi$$100(r), calculate the probability of finding the electron in this region.

I was able to do part (b) and I got 0.238103.
As for part (a), I dont know what to do. I'm able to do the mathematics, I just cant seem to start a problem. Thank you.

## The Attempt at a Solution

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Ehhmmm, but if you have calculated the probability of finding the electron in the classically forbidden region, you already must know what this region is, right?
(and yes, you could have added that to your other post. helps keeping an overview)

vela
Staff Emeritus
Homework Helper

Oh ya grey earl... totally forgot 1-P ...
Vela so part (b) is incorrect? This is how I got the answer...

then the prob of the electron being found in classically forbidden region is (r>2a0)

Then I took the integral of r2 exp(-2r/a0) (4/a0) from 2a0 to infinity... is that not right?

vela
Staff Emeritus
Homework Helper
That's the right method (though I think you meant you had a03 in the denominator). I must have screwed up somewhere in my calculation yesterday. Today, I redid it and got the same answer you did. Sorry to mislead you.

ya sorry i meant cubed. ok good good so i'm on the right track. Thanks so much.

for part (a), i know i would subtract part (b) from 1... but i want to do that actual math.
Does the integral remain the same and just change the limit of integration from 0 to a0 ?

vela
Staff Emeritus