Final answer:
When the Earth is connected to a charged plate, it undergoes a process called grounding, which allows charge to flow from the Earth onto the plate or vice versa. This can result in the plate having an excess of negative charge, causing certain effects such as leaf repulsion in an electro-scope.
Step-by-step explanation:
When the Earth is connected to a charged plate, it undergoes a process called grounding. Grounding allows charge to flow from the Earth onto the plate or vice versa. For example, if a charged rod is brought close to an uncharged electro-scope, touching the metal plate of the electro-scope with a finger while it is connected to the Earth allows charge to flow from the Earth onto the plate. This results in the plate having an excess of negative charge. If the charged rod is then removed, the excess charge on the plate will cause the electro-scope's leaves to repel each other.