A student investigates charging by induction using a lightweight, uncharged conducting sphere suspended from an insulating thread.
As shown in the diagram, a negatively charged rod is brought close to the left side of the sphere without touching it. Simultaneously, the right side of the sphere is momentarily connected to the ground by a conducting wire. The ground connection is then disconnected, and subsequently, the charged rod is removed.
Which of the following correctly describes the final charge state of the sphere and the physical mechanism responsible for it?
Negative charge, because electrons are transferred from the ground onto the sphere.
Positive charge, because electrons are transferred from the sphere to the ground.
Positive charge, because protons are transferred from the ground onto the sphere.
Neutral, because no physical contact was made between the rod and the sphere.