1. The problem statement, all variables and given/known data Before entering a mass spectrometer, ions pass through a velocity selector consisting of parallel plates separated by 1.9 mm and having a potential difference of 120 V. The magnetic field between the plates is 0.42 T. The magnetic field in the mass spectrometer is 1.2 T. (b) Find the difference in the diameters of the orbits of singly ionized 238U and 235U. (The mass of a 235U ion is 3.903x10-25 kg.) 2. Relevant equations Radius = mv/qB 3. The attempt at a solution In order to compare the radii, I need to evaluate the radius expression twice, once for each ion. I'm given the mass of the 235U ion, but I'm unsure as to the charge on either, as well as the mass of the 238U ion.