Why does the electrometer needle deviate if a positively charged glass rod is brought closer to an uncharged hollow ball without touching it?
When a positively charged body is brought to the ball, it finds itself in an external electric field created by this body. Under the action of the field, free electrons in the conductor begin to move to the outside of the ball. On the opposite side there is an excess of positive charge. The appeared positive and negative charges create their own field, the lines of intensity of which are directed opposite to the lines of intensity of the external field. The process of separating positive and negative charges in a conductor occurs until the field created by these charges inside the conductor completely compensates for the external field, that is, the strength of the resulting field inside the conductor becomes zero.
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