An electron of kinetic energy 41 keV moves in a circular orbit perpendicular to a magnetic field of 0.330 T.

Question

(a) Compute the radius of the orbit.
The answer to this part is 2.07mm.
(b) Find the frequency of the motion.
I'm not sure how to find the answer to this part.

Compute the velocity V from the kinetic energy of the electron. The time required to complete 1 orbit is
T = 2 pi R/V
Use the R from part (a)

The frequency of the motion is f = 1/T