Regard as two Styrofoam cups. Each one is on the end of its own neutral slender glass rod which serves as a handle. One of the cups has a fixed amount of positive charge consistently distributed over the entire surface of the cup. The other cup has the similar amount of negative charge uniformly distributed over its entire surface. A person plugs one of the cups with the other cup. Subsequent to the tap what is the sign of the charge of the cup that was originally positively charged?

Ans.:

Styrofoam is an electrical insulator charge doesn't move around in or on Styrofoam. The spot on every one cup where the two touches happen to neutral but the rest of each cup retains its original charges. The net outcome is that the cup that was originally positive is still positive and the cup that was originally negative is still negative. Neither cup has as a lots total charge as it originally had but both cups are still charged.