In this movie you see an electron moving and then entering a magnetic field (B-field). The direction of the B-field is into the screen. Notice that the force created by the magnetic field ends up always pointing to the center of the curve. This force is considered to be a centripetal force (see more in the motion in a plane unit ) because it causes the electron to travel in a circular path.
The screen of your computer (unless it is an LCD) and your television screen both use magnetic fields to deflect electrons fired from an "electron gun". The moving electrons are directed toward different areas of the screen by magnetic fields created by electromagnets. Wherever the electrons strike the screen, they cause phosphorus to give off light. If millions of electrons are directed to the screen in the right places, the little bursts of light leave an impression our eyes which forms an image. An instant later (1/24th of a second) a million more electrons strike the screen and form a new image. Our mind pieces them together to create the impression of smooth motion.
©1998 Science Joy Wagon