Each of the figures below shows the path of a charged particle moving in the plane of the page in a magnetic field that is perpendicular to the page. If the mass , speed and charge of the particle are the same , in which case does the field have the greatest magnitude? Since the mass, speed and charge of the particle are the same, greater magnetic field will produce greater force. `F = qvB` Since the magnetic force is perpendicular to the velocity `v`, greater force means the greater centripetal acceleration `a_c`. `a_c = v^2/r => r = v^2/a_c` greater `a_c` means smaller radius, so answer is D.