What is a Cathode Ray Tube

A Cathode Ray Tube (also known as CRT) is a vacuum tube in which the images are produced. In this the hot cathode emits electrons that are accelerated as a beam. The electrons are passed through a relatively high voltage anode. The images are produced when the electron beam strikes the surface of the monitor which is made up of phosphorous.Most of the desktop monitors used to have cathode ray tube monitors only (which are now being replaced by LCD’s). This cathode ray tube display in a computer is similar to the picture tube display of thee television.

At the back of the monitor there is a set of electron guns. These electron guns produce a stream of electrons. These electron guns start at the top of the screen and then scan very rapidly from left to right. Then these guns return to the left most position one line down and scan again and like this, it repeats the same process again and again until the entire screen is covered. These electron guns need to be controlled for performing this type of function. Thus these are controlled by the video data stream which is coming into the monitor from the video card. This video data stream varies the intensity of the electron beam at each position of the screen.

The complex signals are applied to the deflecting coils and the apparatus (which controls the intensity of the electron beam). This causes the spot to race across the screen in a sequence of horizontal lines called raster. If the movement is observed from the front of the cathode ray tube, the spot moves in a very similar pattern as the movement of the user’s eyes while reading a single column of the text. But this scanning takes place at such a high speed that the naked eyes of the user is not able to observe it and sees a constant image over the entire screen.

The cathode ray tube contains three electron guns within it i.e. red, green and the blue one. Each gun streams a steady flow of electrons (left to right). As soon as the electrons hit the phosphorous surface on the cathode ray tube, the phosphorus starts glowing certain intensities.

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