In this paper, the dynamics of a moving electron in a perpendicular
magnetic field region is examined. It is shown that the angular impulse
plays an important role in determining the change in the electron's speed
when considering the dynamics of motion in two situations. It is shown
that, in the first case, the electron will leave its circular orbit with a speed
equaling half its orbital initial value when the magnetic field is turned
off. In the second situation, the final orbital speed of an electron entering
a perpendicular magnetic field is twice its initial speed. The present
treatment is suitable for undergraduate students as it deepens their
understanding of the dynamics involved in electromagnetic systems.