In the simple mass spectrometer shown in the figure below, positive ions are generated in the ion source. They are released, traveling at very low speed, into the region between two accelerating plates between which there is a potential difference ?V?V. In the shaded region there is a uniform magnetic field B?B?; outside this region there is negligible magnetic field. The semicircle traces the path of one singly charged positive ion of mass MM, which travels through the accelerating plates into the magnetic field region, and hits the ion detector as shown.