TELEVISION LINE BY LINE

foreign [Music] has become a powerful means of communication and today reaches into the lives of almost everyone this film will explain basic principles and demonstrate how pictures are formed on the television too a photoelectric cell and a very sensitive meter are connected with a battery often the semiconductor selenium is used as the resistor in the photoelectric cells when light strikes the semiconductor its resistance is lowered and the flow of electricity is increased if the intensity of the light changes the flow of electricity also changes the resistance is less if the light is strong more if the light is weak this interaction between lights and the resistance of a semiconductor is called photo effect it is one of the basic physical principles involved in television we can measure light with a movable photoelectric cell or light meter we can measure not only the light rays from One Source but the brightness of different objects dark Little Current light more current dark Little Current we can record light and dark areas by making a graph we measure the light intensity of the picture at all points we record the deflection of the pointer with this white curve line by line we record the light intensity of the whole picture following the light intensity curve with a brush we can paint a picture stronger current wider brush stroke weaker current narrower brush stroke what we see is a very much simplified picture of the original object using more lines refines the process and makes the picture clearer in the same manner but with technically more complex equipment pictures can be scanned and reproduced for television the picture is scanned at a very high speed and the rapid succession of single pictures at the rate of 30 per second served to record fluid motions the most important piece of equipment for recording pictures for television is the television camera the pickup or camera cube is the heart of the circuitry of the television camera this is a vidicon tube it is relatively small and simple in construction its principal parts are a light sensitive screen anode and cathode we will follow the process of recording a picture in simplified steps the lens of the television camera projects an image on the light sensitive screen of the viticon 2. screen lies behind the glass face plate the screen is an Emulsion of a light sensitive semiconductor which is spread on a thin transparent plate the signal electrode glass base plate transparent signal plate light sensitive layers the light and dark parts of the image strike the droplets of light sensitive emulsion the resistance of the Emulsion changes where much light strike the resistance is lowered where a little light strikes the resistance is higher the distribution of light in the picture is transformed into resistance in the light sensitive emulsions the resistance at each point must be red to do this we need a beam of electrons at the other end of the viticon tube is a heated Castle which gives off electrons the positive anode catches and accelerates the negatively charged electrons at the same time a magnetic field forms the electron flow into a beam since the beam must scan the entire screen it must be movable we can move the beam using the magnetic fields of two magnets one field moves it horizontally the other vertically using both magnetic fields we can move the beam line by line over the entire picture screen this set of lines is called a scanning pattern now we apply a potential to the signal plate every little spot of the light sensitive Emulsion works as a small condenser the Electron Beam charges the condenser which are discharged again as they are struck by light the various light intensities correspond to different amounts of resistance and the condenser's discharge to a greater or lesser degree with each scanning the process is repeated according to the extent of recharging an electrical current flows between the cathode condensers and the battery the greater the recharging the stronger the current smaller the recharging the weaker the current the variation of the current can be recorded in the form of a curve the Peaks correspond to light areas The Valleys to dark areas of the picture this flow of current is called a television signal it proceeds from the camera to the transmitter and is sent out from the antenna in the form of electromagnetic waves the receiver antenna picks up the waves and delivers them to the television receiver in the television picture cube a beam of electrons is produced and moved as it is in the camera tube a heated cathode releases electrons the electrons are caught by the anode and at the same time are formed into a beam by an electromagnetic field instead of a photoconductive screen the picture tube has a fluorescent screen which gives off light when struck by a beam of electrons stronger light when struck by more electrons weaker light when struck by Fury electrons the electron flow can be changed by the control electrode the electron flow can be made weaker because the control electrode exerts a suppression field that works against the anodes the incoming television signal is fed to the control electrode the incoming signal constantly changes the strength of the suppressing field and the strength of the beam of electrons changes accordingly thus the television signal controls the strengths of the beam of electrons in the picture tube the Electron Beam does not remain still the magnetic fields from two electromagnets move the beam over the fluorescent screen the deflection of the beam horizontally and vertically forms the television picture line by line high line numbers and perfect synchronization of the process of pickup and Playback are the elements which give modern television its high quality from these principles technology has advanced to make it possible to receive images sent across oceans with the aid of satellites and even across Faith from the Moon [Music]