1. The problem statement, all variables and given/known data A small positively charged sphere is lowered by a nonconducting thread into a grounded metal cup without touching the inside surface of the cup. The grounding wire attached to the outside surface is disconnected and the charged sphere is then removed from the cup. What best describes the subsequent distribution of excess charge on the surface of the cup? 3. The attempt at a solution It's a multiple choice question and the answer is "Negative charge resides on the outside surface, and no charge resides on the inside surface." I don't understand why no charge is in the inside surface though. 1. Sphere polarizes cup and ground. Cup is charged negative and ground is "positive". 2. Ground removed. Negative charges are isolated on cup. 3. Charges move to exterior surface of the conductor. Doesn't the "exterior surface of the conductor" include the inside surface of the cup as well as the outside surface?