Faraday's Ice Pail Experiments
First performed by Michael Faraday in 1843, the ice pail experiment demonstrates electrostatic induction. An uncharged metal container (the "ice pail") is connected to an electroscope.
A charged metal sphere is lowered into the container.
The electroscope indicates an induced charge on the container. The charge on the inside of the container is opposite to the charge on the sphere. On the outside it is the same as the charge on the sphere. Since the electroscope is connected to the outside of the pail it will acquire the same sign charge. Overall, negative charge has flowed from the electroscope leaf and electroscope stem towards the positively charged ball. Positive charge cannot move so the leaf and electroscope stem are left positively charged and repel each other.
Moving the charge inside the sphere does not affect the leaf.
The net charge of the whole system is that of the ball.
When the sphere is removed, the electroscope returns to its original state. All the charge flows back and resumes it original distribution.
The net charge of the whole system is zero, as it was being the charged ball was brought near.