experience constructive interference as the electron orbits the nucleus. Thus, the bohr relationship that is analogous to the bragg equation that determines at what angles constructive interference can occur is 2πr=nλ. Both this equation and the analogous bragg equation are illustrations of what we call boundary conditions, they are extra conditions placed on the wavelength to produce some desired character in the resultant wave (in these cases, constructive interference). of course, there remains the question of why one must impose these extra conditions when the Newton dynamics do not require them The resolution of this paradox is one of the things that quantum mechanics does Returning to the above analysis and using n=h/p=h/(mv), 2 r=na, as well as the force-balance equation me v2/r= Ze /r, one can then solve for the radi that stable Bohr orbits obey m and. in turn for the velocities of electrons in these orbits =Ze/(nh/2π) 88 experience constructive interference as the electron orbits the nucleus. Thus, the Bohr relationship that is analogous to the Bragg equation that determines at what angles constructive interference can occur is 2 p r = n l. Both this equation and the analogous Bragg equation are illustrations of what we call boundary conditions; they are extra conditions placed on the wavelength to produce some desired character in the resultant wave (in these cases, constructive interference). Of course, there remains the question of why one must impose these extra conditions when the Newton dynamics do not require them. The resolution of this paradox is one of the things that quantum mechanics does. Returning to the above analysis and using l = h/p = h/(mv), 2p r = nl, as well as the force-balance equation me v2 /r = Ze2 /r2 , one can then solve for the radii that stable Bohr orbits obey: r = (nh/2p) 1/(me Z e2 ) and, in turn for the velocities of electrons in these orbits v = Z e2 /(nh/2p)