3  MOTION IN A MAGNETIC FIELD
We will now consider, in greater detail, the motion of a charge moving in
a  magnetic field We have learnt  in Mechanics (see Class XI book, Chapter
6) that a force on a particle does work if  the force has a component along
(or opposed to) the direction of motion of the particle In the case of motion
of a charge in a magnetic field, the magnetic force is perpendicular to the
velocity of the particle So no work is done and no change in the magnitude
of the velocity is produced (though the direction of momentum may be
changed)