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Not charged due toElectrostatic inductionWhen A is charged, the inner layer of B must be marked withcharge。If B is not grounded, the outer surface of B is charged with the same number as A.If B is grounded, the outer surface of B is not charged.
Electrometer is also called potentiometer or pointer electroscope. It is a semi quantitative measuring instrument commonly used in middle school electrostatic experiments.The central rod A including ball a and pointer bc is fixed on the round metal shell B with front and rear glass windows with insulating plug D;There is a terminal under the side of B;The whole unit is fixed on an insulating support.
When A is charged, the charge is mainly distributed at the four tips of a, b, c and d. Among them, the charge carried by c and d is repulsive, and the pointer is subject to an electric moment L1 that opens it.Since the center of gravity of the pointer is slightly below the point O of the rotation axis, when L1 opens the pointer, the gravity of the pointer will generate a gravity moment L2 that resets the pointer.As the pointer deflects, L1 decreases (because the distance between c and d increases,Coulomb forceSmaller,Lever armAnd L2 becomes larger (because the gravity arm increases).When L1 and L2 are equal, the pointer stops at a certain position (stable balance), and the angle of the pointer is α °
When the charged quantity q of A is large, the charged quantity of c and d is also large, and L1 is large, so α is also large.Since q determines α, the size of α can represent the size of q.This is why electrometer can be used as electroscope.
