The mass spectrometer is a device used to study isotopes of ions produced in a cathode ray tube. Isotopes of an element share the same chemical properties but have different masses and produce different values for their charge-to-mass ratio. An electron beam strikes vapor atoms that yield positive ions accelerated by a potential difference and deflected by a uniform magnetic field to hit a photographic plate. Mass spectrometry can also be used to identify molecules by analyzing the masses of its fragments.