An electron and a proton are both moving in a circle in the x–y plane due to the force produced by a magnetic field perpendicular to the plane (Fig. P20.39).
(a) If the electron moves clockwise and the proton moves counterclockwise, is the magnetic field directed into the plane or out of the plane of the drawing?
(b) If the circular paths followed by the electron and proton have the same radii, what is the ratio of their speeds?

Proton Electron