Write the expression for the magnetic force `vecF` acting on a charged particle `q` moving with velocity `vecv` in the presence of the magnetic field `vecB` in a vector form.
Show that no work is done and no change in the magnitude of the velocity of the particle is produced by this force.

Explanation

As the force `vecF` is acting in a direction perpendicular to both `vecv and vecB`, it does not do any work on the charged particle (because work `W = F cos 90^@ = 0)`. Moreover, being normal to `vecv`, it can change only the direction of velocity but cannot change the magnitude of velocity.