Explain Raster Scan
In Raster scan, the electron beam from electron gun is swept horizontally across the phosphor one row at time from top to bottom. The electron beam sweeps back and forth from left to right across the screen. The beam is on, while it moves from left to right. The beam is off, when it moves back from right to left. This phenomenon is called the horizontal retrace. As soon as the beam reaches the bottom of the screen, it is turned off and is rapidly retraced back to the top to start again. This is called the vertical retrace. Raster scan displays maintain the steady image on the screen by repeating scanning of the same image. This process is known as refreshing of screen.