Now I'm reading a book QM, scattering problen when an electron is scattered by an atomic nucleus, and stuck at a simple formula; [tex]\int_0^\infty \varrho_p(R) R^4 dR = \langle R^2 \rangle,[/tex] where [tex]\varrho_p(R)[/tex] is the charge density at radius = [tex]R[/tex] In this formula, electric charge unit [tex]e[/tex] is omitted.(adsbygoogle = window.adsbygoogle || []).push({});

As a matter of course, [tex]4\pi \int_0^\infty \varrho_p (R) R^2 dR = Z[/tex] holds.

Will anyone tell me why the first equation holds?

Thanks in advance.

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# (maybe) simple calculation question

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