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In a cathode ray tube, a series of electrodes produces a narrow, tightly focussed beam of electrons. This beam is then deflected horizontally or vertically, either by other electrodes or by external magnetic fields. The beam travels a distance, typically on the order of one or two feet, and strikes a flat screen covered with phosphors. The phosphors glow where the beam strikes, causing a bright dot of light.
In a cathode ray tube, a series of electrodes produces a narrow, tightly focussed beam of electrons. This beam is then deflected horizontally or vertically, either by other electrodes or by external magnetic fields. The beam travels a distance, typically on the order of one or two feet, and strikes a flat screen covered with phosphors. The phosphors glow where the beam strikes, causing a bright dot of light.
Cathode-ray tubes were very important electronic devices throughout most of the twentieth century. They found application in the early part of the century in oscilloscopes, a piece of technical equipment used in scientific research and electrical engineering. During the Second World War, they were used as radar screens. After the war, they became ubiquitous as television "picture tubes."
Driven by the huge volume of consumer applications, cathode-ray tubes advanced enormously in the second half of the century. Very large tubes were developed in order to meet the need for large television screens. The glass envelopes, originally circular in shape, became rectangular to save space. Various forms of color CRTs were developed, the commonest employed three separate electron beams, three different colors of phosphor dots, and a "shadow mask" insure that each beam struck only the dots of its corresponding color. As computers became common in the last quarter of a century, color CRTs became sharper and higher in resolution, and the screen itself—original shaped like a section of a sphere centered on the electron gun—became shallower and, eventually, completely flat, to minimize reflections.