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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
scott712 wrote ...
Why do Van de Graaf generators use needle combs to make electrical contacts between the belt and the inside of the sphere?
As a charged conductor is brought to a point, the charge density on the surface of the conductor increases. In the case of the VDG combs, the charge density reaches a level where an ionic wind streams from the point, spraying the charge onto the nearest conductor having a potential difference.
This is why even very small irregularities - including dust - on the surface of a VDG accumulator sphere will cause a serious loss of the sphere's ability to accumulate and hold a charge.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
It's also possible to use brushes, with a small improvement. Very light brushes, to not scratch the belt. Look at the brushes that discharge the paper in a laser printer. They work well. And work well also as combs if they don't touch the belt.
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VDG Needle Question
