Explain refresh cathode ray tube ?

A beam of electrons, emitted by an electron gun, passes through focusing and deflection systems that direct the beam toward specified positions on the phosphor coated area.
The phosphor that emits a small spot of light at each positionm contacted by the electron beam.
One way to keep phosphor glowing is to redraw the picture repeatedly by quickly directing the electron beam back over the same points.
This type of display is called is called refresh CRT.
Primary components of electron gun are:

Heated metal cathode
Heat is supplied to the cathode by directing the
beam through a coil of wire called the filament
inside the cylindrical cathode structure.
Control grid
Intensity of the electron beam is controlled by
setting the voltage levels on the control grid, which
is a metal cylinder that fits to the cathode.

Different kinds of phosphorus are available.
Besides color the major difference between phosphors is their persistence.
The maximum number of points that can be displayed without overlap on a CRT is referred to as resolution.
Another property is aspect ratio.

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