Cathode-Ray Tube.
People who think
vacuum tubes are obsolete clearly haven't looked in their
television set. CRT's work by using an electron gun at the back, which uses a heater to liberate
electrons from the
cathode. A high
voltage electric field exists between the cathode and the
anode, which is located further into the tube. This
accelerates the
electrons to a
high speed. During
transit, deflection
coils located on the neck of the CRT bend the resultant
beam so that it can hit different parts of a phosphor coated
screen. There are also
focusing coils, correction
magnets and other devices on the
tube to insure uniform focus and
illumination.
By
moving the beam around, you can draw pictures. You can either draw
vector graphics by using the beam itself to
draw the picture, or you can generate a
raster by scanning the entire screen several times a
second and modulating the brightness to produce an
image.
There are also
color CRT's, which use
three electron guns, a
shadow mask, and
red,
green, and
blue phosphors to produce full color images.