HOW TELEVISION WORKS

foreign this sort of thing becomes ever more common each one is a television aerial of which there are several kinds not all of which are in the open from each aerial a wire leads inside the house to a television receiver want these viewers see going on in their television set is really happening at almost the very same moment but in a different place [Music] we are now in the television Studio the picture will usually be taken by more than one camera so that by switching over the viewer is given an instant change of view [Music] the sound is picked up by a microphone and broadcast exactly as an ordinary Sound Radio the picture however is separately dealt with it is viewed by one of the television cameras the camera has lenses like any other camera but there the likeness ends the lens in the case of this camera does not put the picture onto a film but onto the end of a special vacuum tube here is the tube this is the window end on which the lens throws a moving picture but for the rest there are only electrical connections it is inside the tube then that the picture is changed into electrical impulses for this two parts are mainly used the first is behind the window and is called the mosaic although it appears transparent this side is actually covered with tinier separate squares of metal here they are very much enlarged the second part called the electron gun can be made to project a continuous stream of tiny electrical particles called electrons at the Mosaic through the tiny hole in the middle this tubular device is used to change the direction of the stream of electrons on the Mosaic is the picture of the piano keys the metal squares have been made very much larger to change the picture into electrical impulses here is the stream of electrons it is rarely quite invisible this is the tubular device it can deflect the stream of electrons up and down and from side to side it is used to move the stream across the picture space a line at a time until all the space has been sprayed when it sets the stream back to the start the stream keeps spraying the Mosaic like this over and over again so that we can see what happens the stream in the drawing crosses that is slowly and it only has to cross 16 times to cover the mosaic in the real thing the stream makes several hundred Crossings to cover the Mosaic and covers it 50 times each second let's stop the movement of the Stream now here is a while when the stream hits a bright metal square a strong impulse of electricity goes along the wire when the stream hits each gray Square each impulse is weaker and when it hits each dark Square each impulse is very weak indeed so now the picture a pattern of different intensities of Light which we could see has changed the strength of a flow of electricity into a pattern of different impulses which cannot normally ever seen but can be carried along the wire from the tube the wires carrying the impulses of electricity which now represent the picture go to this apparatus called an amplifier because it strengthens the impulses from the camera in the studio cables carry the strengthened impulses to a control room here the impulses are further Amplified and undergo complicated technical processes before passing to the actual transmitter where they modulate the radio signal that is to broadcast them to broadcast means to send out in all directions which is done from the top of this very tall Mast by this very small aerial almost at once the receiving aerial is passing the same impulses which by now are very much weaker to the television set they go first to this amplifier apparatus because they are so weak and now very much stronger the impulses are fed to this tube this end receives the impulses from the amplifier this end is where the picture appears the tube is very like the tube in the camera in having two main parts the gun that projects a stream of electrons and the other part instead of being a mosaic is the end of the tube itself on its inside surface is a coating of material or forming a fluorescent screen that is also this part which deflects the electrons just as there was for the camera tube here are the wires one of which brings the successive impulses of electricity here is the fluorescent screen here is the deflecting device from the gun a stream of electrons is projected the deflecting device bends the stream to spray like the stream in the camera tube but the stream is bent more this time to cover a larger screen area as the electrons are sprayed on it the fluorescent screen glows so that where the stream hits can be seen but all the time the electrical impulses are coming in some very strong from the bright part of the picture some of medium strength from the gray part of the picture and some very weak from the dark part of the picture these different impulses are made to alter the Stream strong impulses strengthen the Stream and weak impulses weakened it almost to nothing a very weak stream doesn't make the fluorescent screen shine at all leaving black on the screen a medium strength stream makes the screen shine more or less to make with gray parts of the picture and a strong stream makes the screen shine brightly giving the patches of white the screen doesn't shine for very long though the bright paths soon fail but you will remember that the stream travels much faster than this it makes hundreds of lines 50 times a second so that almost before a bright part has time to fade the stream is back again to brighten it fifty images are painted each second so the illusion of a smoothly moving picture is readily accepted because the eyes of the viewer are quite unable to distinguish the separate images let's run over it again here is the piano to be televised its picture is taken by a special camera the camera turns the black white and gray of the picture into electrical impulses which pass from the camera to the broadcasting station where the impulses are strengthened and sent out by the aerial practically at once the impulses reach the Aerials on folks homes and go to the receiver here the electrical impulses are turned back into the black white and gray of a picture 50 image images are painted each second this is much too fast for our eyes to separate and so we see apparently a continuous moving picture at almost the same time as it actually happens [Music] thank you foreign [Music]