Physics
Physics
Problem
A neutral metal sphere rests on an insulating stand. A negatively charged rod is held near the sphere without touching it. While the rod is in place, the sphere is grounded by touching it briefly with a finger. After removing your finger and then taking the rod far away, describe the net charge that remains on the sphere and explain your reasoning in one or two sentences.Intuitive explanation
The key insight is understanding electrostatic induction and what grounding actually does: the negative rod repels electrons in the conductor to the far side, but grounding provides a path for excess electrons to escape to Earth. Once the rod is removed, those electrons can't return, leaving the sphere with a net positive charge. Think of grounding as a one-way valve that lets the conductor shed its pushed-away charge.
Intuitive explanation
The key insight is understanding electrostatic induction and what grounding actually does: the negative rod repels electrons in the conductor to the far side, but grounding provides a path for excess electrons to escape to Earth. Once the rod is removed, those electrons can't return, leaving the sphere with a net positive charge. Think of grounding as a one-way valve that lets the conductor shed its pushed-away charge.