Cathode and Cathode-ray Tube

Source:  Cathode and Cathode-ray Tube    Tag:  cathode ray tube electron

A cathode is the terminal, or electrode, through which a positive electrical current exist (or negative current enters) an electrical device. (The other electrode is the anode.) in electrolysis, the negatively charged electrode immerse in a cell containing an electrolyte (a chemical mixture or compound that conducts electricity) is called the cathode. In an electron tube, the cathode is the electrode from which a stream of electrons is emitted.

Cathode-ray Tube
The cathode-ray tube, often abbreviated CRT is an electron tube that provides a visual display of information. The tube’s glass envelope is at the tube’s narrow end generates a stream of electrons. (Before the discovery of the electron, such a stream was known as a cathode-ray). As they pass through one or more cylinder electrodes, the electrons are focused into a pencil-shaped beam. The electron beam then pass through a deflection section where it is shifted either vertically or horizontally in response to an external signal. The deflection may be caused by passing a current through electromagnetic deflection coils that encircle the tubes, by applying a voltage to one or more of four deflection electrodes arranged around the beam’s path. After the electron beam has been deflected. It strike a light emitting layer or phosphor on the inside wall of the tube’s face. The electrons cause the phosphor to fluorescence and the resulting glow becomes a point of light on the face of the screen. Various phosphors or combinations of phosphors can be used to produce all the colors of the visible spectrum.

The cathode ray tube is by far the most important electronic visual display used today. Its best known application is in Television. The circuitry in television receives causes the electron beam in the CRT to continuously sweep across the screen in a pattern of hundreds of closely spaced horizontal lines at a rapid rate. A similar Scanning pattern is used in the TV camera. By synchronizing the camera’s signal with the receiver’s sweep circuits, the electron beam can be activated and deactivated in step with the signal. The result is an image on the face of the cathode-ray tube that reduces the image picked up by the camera. Other uses for the CRT include the visual display for an oscilloscope and the video display unit for a computer.