(a) Write the expression for the force `vecF` acting on a particle of mass m and charge q moving with velocity `vecv` in a magnetic field `vecB`. Under what conditions will it move in (i) a circular path and (ii) a helical path?
(b) Show that the kinetic enery of the particle moving in magnetic field remains constant.

Explanation

(a) (i) If direction of `vecv` is at right angles to that of `vecB`, the charged particles will moave in a circular path.
(ii) If `vecv` is inclined to `vecB` at an angle `theta`, where `theta != 0^@` or `pi/2` or `pi`, the charged particle will move in a helical path.