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Cathode Ray Tube
How the technology works
The cathode-ray tube provides a visual display in the following way: (1) its thermionic cathode produces a stream of electrons; (2) an electric field accelerates the stream of electrons to a desired velocity, or energy level; (3) an electron lens focuses the stream of electrons into an electron beam that has a very small cross section; (4) an electric or magnetic field is used to deflect the focused beam through a prescribed angle; (5) the deflected beam hits a small area of a transparent glass surface coated on the inside with a phosphorescent material that emits light when an electron beam strikes it with sufficient energy; and (6) if the electron beam is swept rapidly and repeatedly across the cathode-ray tube screen, a line of varying intensity is produced rather than a sequence of discrete spots. A complete image of the television type is formed by producing a number of lines on the screen.
Advantages of the technology
An electron gun consists of three major parts. The first is the cathode—a piece of metal which, when heated, gives off electrons. One of the most common cathodes in use is made of cesium metal, a member of the alkali family that loses electrons very easily. When a cesium cathode is heated to a temperature of about 1750F , it begins to release a stream of electrons. These electrons are then accelerated by an anode placed a short distance away from the cathode. As the electrons are accelerated, they pass through a small hole in the anode into the center of the cathode-ray tube.
Disadvantages of the technology
They are bulky. In order to increase the screen width in a CRT set, you also have to increase the length of the tube (to give the scanning electron gun room to reach all parts of the screen). Consequently, any big-screen CRT television is going to weigh a ton and take up a sizable chunk of a room.
Around $13-$30.
Price range of the technology
