A student rubs a rubber rod with fur, producing a negative charge on the rod. The student then touches the rod to a hollow, neutral metal sphere that stands on an insulating plastic stand. This transfers negative charges from the rod to the sphere:
Which statement best predicts what will happen to the charge, and why?
A. It will quickly spread to the air around the sphere, because it will seek to occupy as large a volume of neutral matter as possible.
B. It will remain at the point of contact between the rod and the sphere, because resistance in the metal prevents the charges from easily moving.
C. It will distribute itself evenly over the surface of the sphere, because like charges repel and the sphere is a conductor.
D. It will slowly drift to the bottom of the sphere, because the charges rapidly attach to individual atoms, making them slightly heavier than surrounding atoms.
The correct answer is C. It will distribute itself evenly over the surface of the sphere, because like charges repel and the sphere is a conductor.
When the negatively charged rod touches the neutral metal sphere, the negative charges on the rod will repel the negative charges on the surface of the sphere. This repulsion will cause the negative charges to spread out across the surface of the sphere in order to minimize the repulsive forces between them. Additionally, the metal sphere is a conductor, which means that the negative charges can easily move through it. Therefore, the negative charges will distribute themselves evenly over the surface of the sphere.