00:01
So we're interested in the z component of angular momentum operator in quantum mechanics.
00:08
So we're going to start out by looking at what we call partial phi.
00:15
This is the operator that acts like a derivative with respect to the azimuthal angle phi.
00:23
I've written out x, y, and z here in spherical coordinates.
00:32
And so what we're going to do, first of all, let's, does take these derivatives and substitute in.
00:42
So partial x, partial phi, is minus r -sign theta, sine phi.
00:52
It'll be partial x, plus partial y, partial phi would be r -sin -theta -cosine -fi, partial with respect to y.
01:07
And then the root of z with respect to phi is zero.
01:14
And i can look at this and recognize r -sign theta cosine -fi, that's x, and r -sign theta -sign -fi is y.
01:23
So this is x, partial y, minus y, partial x.
01:32
So that was the first part.
01:36
The second part of the problem, we want to think about the angular momentum operator.
01:46
So the angular momentum operator looks like r cross p.
01:53
And in particular, i'm going to look at the z component of angular momentum.
02:01
So lz, if i think about this product, cross product, is x, p .y minus y p .x...