ABC
of Television
Have you ever wondered how a Television works?
Well lets see the basic mechanics of Television.
Today Television has become a part of our lifes. We use
television to see movies, news , sports events etc. On a
TV Screen there are dots which we call them as Pixels.
For e.g in computers we set screen resolution to
800 X 600 pixels or 1024
X 768
pixels according to users choice.
Cathode
Ray Tube:
It is a vacuum tube in
which a hot cathode emits a beam of electrons that pass
through a high voltage anode and are focused or
deflected before hitting a phosphorescent screen.
Inside CRT
Inside a CRT Tube
there is a filament (heater), a cathode, a control grid,
accelerating anode, focusing anode and plates for
horizontal & vertical deflection.
The cathode
temperature is raised by the heater, and electrons
evaporate from the surface of the cathode.
The focusing
anode ensures that electrons leaving the cathode are
focused down to a narrow beam and all come at the
same spot on the phosphorescent screen.
The accelerating anode
is kept at a high positive potential of the order
of 1 to 20 kV, relative to the cathode.
This potential
difference gives rise to an electric field directed from
right to left in the region between the accelerating
anode and the cathode.
Electrons forms
a narrow beam and travel with constant horizontal
velocity from the anode to the fluorescent screen. The
area where the electrons strike the
phosphorescent screen glows
brightly.
The function of control
grid is to regulate the number of electrons that reach
the anode.
Together cathode,
control grid, accelerating anode, & focusing anode is
called as ELECTRON GUN.
The beam of electrons
passes between two pairs of deflecting plates. An
electric field between the first pair of plates deflects
the electrons horizontally, and an electric field
between the second pair deflects them vertically. If no
deflecting fields are there, the electrons travel in a
straight line from the hole in the accelerating anode to
the center of the screen, where its produces a bright
spot on phosphorescent screen.
