[填空题]
Use the uncertainty principle to show that if an electron we)i5fi1sv-4h jofoj;s /m+qbxti-d 7 w re present in themk.m al 0 itht tbe/o::or+w/lh(;e7d nucleubm. lot7ht k/;mt+/do:a0e: il(hwer s $(r \approx 10^{-15} \, \text{m})$, its kinetic energy (use relativity) would be hundreds of MeV. (Since such electron energies are not observed, we conclude that electrons are not present in the nucleus.) [Hint: A particle can have an energy at least as large as its uncertainty.]
E $\approx$ Mev
