Question:
I am doing a simple science project with my son. I accidently waived a magnet by a
CRT screen and saw the magnetic fields in colors. I want to do this experiment at the school
along with a 4th grade explanation on the reaction between screen and magnet. Can you help?
Replies:
NoName,
On a CRT, the picture is drawn by three separate electron beams scanned rapidly across the screen.
Each bean is supposed to strike only one of the three primary color phosphors on the interior of
the CRT face. The beams are guided to their proper location by the interplay of electric and
magnetic fields applied back in the area of the CRT tube's neck.
When you applied the magnet to the CRT face, the externally imposed magnetic field distorted the
aim of the electron beams, thereby causing a mis-registration of their intended points of impact.
Older color TV sets can be temporarily damaged by application of a magnet to the screen. No
damage will occur if the TV CRT is of the black and white style.
Regards,
ProfHoff 641
This is similar to the generation of electrical current by moving a wire through a magnetic
field.
In this case, you have an electrical current moving through a magnetic field. A force is
generated that causes the electrons moving toward the screen to be displaced slightly and
hit the wrong color dot.
Color CRTs work by superimposing three images -- one Red, one Blue, one Green -- at least
this is one color scheme that is used. It takes precise alignment of the electron beams to do
this. The interaction of the moving electron beam with the magnetic field causes the electrons
to shift slightly and hit the wrong color dots.
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