Television: How TV Works

The “moving parts” of television are two slim beams of electrons that sweep back & forth 15,750 times in each second. One “scans” the optical image of the scene the “pickup tube” is looking at. The other listens carefully, miles away, and paints an almost identical picture on the screen of the receiver.

Ordinary light knocks electrons from certain substances. The stronger the light, the more electrons it detaches. In the television “camera,” a lens focuses a picture of the scene on a light-sensitive coating inside the pickup tube’s front end. Electrons fly off. They are focused on a thin glass plate, each knocking off several more electrons, which are gathered up by a charged screen and drawn out of the tube.

Since electrons are negative electricity, their departure covers the glass with an invisible picture in positive electricity. A beam of electrons from the other end of the tube is swept across the picture by deflecting coils, which steer it. When the beam hits a strongly positive area, a good many of its electrons are attracted into the glass by the positive charge. When it crosses “shadows,” only a few electrons stick. The rest bounce back and are gathered up by charged metal surfaces at the small end of the tube.

The result is an electric current which fluctuates rapidly to match the picture. This current is amplified and sent by a radio transmitter to the television receiver, where it controls the strength of a second electron beam in a rather similar tube.

At the big end of the receiving tube or “kinescope” is a screen of material that glows brightly when electrons are hurled at it As the beam sweeps across the screen, it duplicates in light the picture that the television camera is seeing.