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## Main Question or Discussion Point

I'm trying to learn QM on my own, and I've encountered some conceptual issues. The textbook that I'm working from just glazes over everything.

I appreciate all help in trying to get over the learning curve for QM.

- What is a wave packet? I know how to calculate wave packets, but how does a wave packet relate to the wave function?
- What is the conceptual difference between the probability density and the probability amplitude? (I know [itex]|\psi|^2[/itex] vs. [itex]\psi[/itex]...but what do they represent?)
- What is the difference between the group velocity and the phase velocity? Moreover, where does the relation [tex]v_g = \frac{\partial \omega}{\partial k}[/tex] come from?
- How can I determine a particle's momentum from wavepackets/wavefunctions?
- In which direction do a particle's matter waves propagate? (I need to know this because I am not sure why Bohr was able to calculate the standing waves in the hydrogen orbit until I understand in which direction the matter waves move.)

I appreciate all help in trying to get over the learning curve for QM.

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