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Charging an insulator

by akhil123
Tags: charging, insulator
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akhil123
#1
Jan29-10, 06:16 AM
P: 14
When a charged body is brought near an insulator, the side facing it acquires a charge of opposite sign because of induction. Is it possible for an insulator to acquire same charge as charged body? (by induction, touching or any other means)
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GRDixon
#2
Jan29-10, 09:53 AM
P: 250
Quote Quote by akhil123 View Post
When a charged body is brought near an insulator, the side facing it acquires a charge of opposite sign because of induction. Is it possible for an insulator to acquire same charge as charged body? (by induction, touching or any other means)
Yes. The belt on a van deGraaff generator picks up charge in this way.
Bob S
#3
Jan29-10, 12:07 PM
P: 4,663
An insulator in an electric field gets charged positively by field-emission of electrons in very high electric fields, or negatively by electrons collected from other field-emitting sources. Charge cannot be induced (Faraday induction) on insulators. In very high voltage situations, charge can get deposited in (as opposed to on) insulators.

Bob S

GRDixon
#4
Jan29-10, 02:15 PM
P: 250
Charging an insulator

Quote Quote by Bob S View Post
An insulator in an electric field gets charged positively by field-emission of electrons in very high electric fields, or negatively by electrons collected from other field-emitting sources. Charge cannot be induced (Faraday induction) on insulators. In very high voltage situations, charge can get deposited in (as opposed to on) insulators.

Bob S
I was referring to the "other means" part of the question. In the Wikipedia description of a van deGraaff generator, it looks to me like the combs "wipe" charge onto (or into) the conducting, dielectric belt. Once conveyed to the large metal sphere at the top of the loop, the charges are wiped off of (or out of) the belt by the upper comb, and migrate to the sphere's outer surface where they can build up considerably before spontaneously draining away into the ambient air.
akhil123
#5
Jan30-10, 11:05 AM
P: 14
Thanks a lot
GRDixon
#6
Jan30-10, 01:05 PM
P: 250
Quote Quote by akhil123 View Post
Thanks a lot
You're welcome. I know the "scraping" idea is a lame one, but it was how one of these contraptions was explained to me in a highschool physics class.


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