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# Angular momentum operator (Quantum angular momentum)

nosplit "Uncertainty principle" words: 147
Basically the operators are just analogous to the classical ones e.g. the classical: $$Lz​=xpy​−ypx​ (22)$$ becomes: $$L^z​=−iℏ(x∂y∂​−y∂x∂​) (23)$$
Besides the angular momentum in each direction, we also have the total angular momentum: $$L^2=L^x​+L^y​+L^z​ (24)$$
Then you have to understand what each one of those does to the each atomic orbital:
There is an uncertainty principle between the x, y and z angular momentums, we can only measure one of them with certainty at a time. Video 17. "Quantum Mechanics 7a - Angular Momentum I by ViaScience (2013)" justifies this intuitively by mentioning that this is analogous to precession: if you try to measure electrons e.g. with the Zeeman effect the precess on the other directions which you end up modifing.