Item C of two physics questions in senior high school is to connect the inner wall of the metal shell with the metal ball of the electroscope with wires. Why can the metal foil of the seventh question be opened? The electroscope is very sensitive, and a very small amount of charge can make its two foils open (note that it is very small). The charged hollow conductor in the seventh question can be understood as a high potential body with a large number of positive charges. After it is connected with the electroscope by a wire, a current is generated in the wire until the charges are equally divided and the charges of the two objects are equal. At this time, there is still enough charge to turn on and maintain the electroscope.