Here's a silly question. I'm sure I should know the answer, but alas my most recent QM course was 9 years ago.(adsbygoogle = window.adsbygoogle || []).push({});

I sat down to calculate the expectation value of momentum in the H-atom today, because some kid on another forum wanted to know how fast an electron in an atom is. I was going to calculate [itex]<p>[/itex] and divide it by [itex]m[/itex] for him.

So I wrote down [itex]<p>=\int_V\psi_{100}^*(-i\hbar\nabla)\psi_{100} d^3x[/itex] ([itex]\psi_{100}[/itex] being the ground state H-atom wavefunction). Upon noticing that I've got a solitary [itex]i[/itex] sandwiched between two purely real functions, I didn't even bother to continue. It's going to come out imaginary.

What am I doing wrong?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Expectation Value of Momentum in H-Atom

**Physics Forums | Science Articles, Homework Help, Discussion**