The ratio of charge to mass, expressed as e/m, of a particle. The acceleration of a particle in electromagnetic fields is proportional to its specific charge. Specific charge can be determined by measuring the velocity υ which the particle acquires in falling through an electric potential V (υ = √2eV/m ); by measuring the frequency of revolution in a magnetic field H (the so-called cyclotron frequency ω = eH/mc, where c is the velocity of light); or by observing the orbit of the particles in combined electric and magnetic fields. In the mass spectrograph, the fields are arranged so that particles of differing velocities but of the same e/m are focused at a point.