A metal sphere is initially neutral. It is connected to the ground by a metal wire. A positively charged rod is brought close to the metal sphere.

A metal sphere is initially neutral. It is connect

Three students are having a discussion as to the charge state of the metal sphere when the rod is close to the sphere.

Student A: The metal sphere will be neutral. The electrons in the sphere will move closer to the rod. The positive charges will be pushed away. But the positive charges cannot move through the wire into the ground. So the sphere will be polarized but still neutral.

Student B: The metal sphere will be positively charged. The electrons in the metal sphere will flow through the wire into the ground. That is the meaning of grounding. So the sphere will be left with excess positive charges.

Student C: A is correct. The sphere will be polarized with the electrons close to the rod. The positive charges at the farther end will attract electrons from the ground which flow from the ground into the sphere through the wire. This will result in the sphere having an excess negative charge.

Which student do you agree with and why? Discuss all parts of the statements made by all three students and explain where the reasoning is right or wrong. Be sure to address all parts of all three statements. If you do not agree with any of them then explain what will happen in this situation.

The sphere is initially neutral. When a positively charged rod is brought close to the sphere, due to induction, electrons would move to the side closer to the rod leaving positive ions on the other side. The sphere would have been still been neutral yet polarized if the sphere were not grounded. As the sphere is grounded, the electrons would flow from the ground to the sphere and neutralize the positive charge at the end leaving the sphere with the net excess negative charge.

Thus, student C is correct.