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Name: Unknown
Status: other
Age: 40s
Location: N/A
Country: N/A
Date: 4/9/2003


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.

Greg Bradburn



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