Describe the Working of CRT
The electron beam produces a tiny, bright visible spot when it strikes the phosphor-coated screen. A colour CRT monitor has three different coloured phosphors arranged in triangular groups called triads. Each triad consists of three phosphors of colours - red, green and blue. So there are three electron guns - one for the primary colour red, one for the primary colour green, and one for the primary colour blue, each of which generates an electron beam to excite one of the phosphor dots. The CRT, thus, produces three overlapping images : one in red (R), one in green (G) and one in blue (B). This is the so-called RGB colour model. In order to ensure that an electron beam activates only phosphors of proper colour, a metal grid called shadow mask
Different coloured light is generated at the screen position hit by the electron beam according to the phosphor type, which fades quickly in 10 to 60 microseconds. Fading time depends on the persistence (the time from the removal of the excitation to the moment when phospherescence has decayed to 10% of the initial light output) of phosphor coated inside the screen. In order to avoid flickering picture should be kept on the screen for a while, the picture should be redrawn before it disappears off the screen. This is called refreshing of the screen.