27.32 . A singly ionized (one electron removed) 40K atom passes
through a velocity selector consisting of uniform perpendicular
electric and magnetic fields. The selector is adjusted to allow ions
having a speed of 4.50 km s to pass through undeflected when the
magnetic field is 0.0250 T. The ions next enter a second uniform
magnetic field oriented at right angles to their velocity. 40K
contains 19 protons and 21 neutrons and has a mass of
(a) What is the magnitude of the electric field in
the velocity selector? (b) What must be the magnitude of so that
the ions will be bent into a semicircle of radius 12.5 cm?