The electric field between the plates of the velocity selector in a Bainbridege mass spectrometer is 20 V/m, and the magnectic field in both regions is 10 T(out and inside the spectrometer). A stream of singly charged selenium ions moves in a circular path with a radius of 1 m in the magnectic field(after they come out from the spectrometer). Determine the mass of one selenium ion. How do I get the mass when I don't know the charge? I know that v=E/B and Forces equal but I just can't find M without knowing the charge.