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TELEVISION

1. Television works on a similar principle to radio except that two signals have to be transmitted one for the sound and one for the vision. In the receiver these signals, which are close to each other in frequency, have to be amplified and separated.
2. The separator contains two resonant circuits, one tuned to the frequency of the sound carrier-wave. The sound signal is then dealt with in the same way as a sound receiver. The picture is formed by making a beam of electrons move across the screen of a cathode ray tube, variation in the intensity of the beam causing areas of transmission — these are the number of lines that can be seen making up the picture. With interlaced scanning the whole screen is covered by half the number of lines in l/50th of a second — this is called a frame.
3. The television camera consists of an optical lens system similar to the lens used in a photographic camera, the image from which is projected into a camera tube. This consists of a photosensitive mosaic scanned by an electron beam. All are housed in an evacuated glass tube. The output signals of the camera tube are usually preamplified within the body of the camera.
4. Colour TV works on the same principle, the camera having three separate tubes, each sensitive to one of the three colours red, green, or blue. In the receiver the cathode ray tube has three electron guns, each one is controlled by the appropriate tube in the camera. The screen of the CRT is coated with a mosaic of different colour spots that fluoresce when electrons from a particular gun strike them, all the colours are made up from blends of the three colours.

Ответить на вопросы по тексту:

1). What is the basic principle of television work?
2). How many circuits are there in the separator?
3). What is a frame?