The electron's brother is the neutrino which has no mass and no charge, but is similar to the electron in most every other way. The theory is that if you take away the electron's charge, then it will become a neutrino. In other words, the mass of the electron is entirely due to its electrostatic self energy U=12ke2r0 where r0 is the "classical electron radius" (we assume the electron is a ball with all of the charge on its surface).
A) Given that the electron's mass in energy units is 0.511 MeV (recall MeV=1,000,000 eV, and 1eV=1.6×10?19 Joules), calculate its classical radius r0.
B) The electron has a heavier cousin called the "muon". Its mass is 207 times that of an electron, but it has the same fundamental charge. What would be its classical radius?