Problem 6.22

Calculate for a hydrogen atom and a $\mathrm{He}^{+}$ ion: (a) the radius of the first Bohr orbit and the velocity of an electron moving along it; (b) the kinetic energy and the binding energy of an electron in the ground state; (c) the ionization potential, the first excitation potential and the wavelength of the resonance line $\left(n^{\prime}=2 \rightarrow n=1\right)$.