# Both Fields at Once?!

Pertinent to their ongoing investigation of MRI machines, students learn the consequences of a charge being subject to electric and magnetic fields at the same time. The lesson covers the Hall effect, velocity selector and the charge to mass ratio. Through several example problems, students calculate the Hall voltage, which is dependent upon plate width, drift velocity and magnetic field strength. Then they calculate the velocity selector, represented by the ratio of the magnitude of the fields, assuming the strength of each field is known. Students perform a series of calculations to arrive at the charge to mass ratio, and finally, a homework problem set, serving as an evaluation of student progress.