A metal sphere is mounted on an insulating stand in a physics laboratory
PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Electric Force Field and Potential · Electric Force Field and Potential
Problem
A metal sphere is mounted on an insulating stand in a physics laboratory. In two separate trials, the sphere is found to carry (i) a net charge of −4.0μC and (ii) a net charge of +4.0μC. In each trial the sphere is momentarily connected to Earth through a long metal wire and then the wire is removed.
Assume the Earth is an enormous reservoir that remains electrically neutral overall.
Answer the following questions for each trial, clearly indicating the direction of charge movement between the sphere and Earth and the role of charge conservation.
(a) For the negatively charged sphere, describe qualitatively the movement of charge that occurs while the wire is attached. Indicate the direction of electron flow and state the sign of any charge that leaves or enters the sphere.
(b) For the positively charged sphere, repeat the description requested in part (a).
(c) Using the law of conservation of electric charge, explain why the sphere is left electrically neutral in both trials even though the Earth contains an effectively infinite number of charges.
(d) Compare the two trials to clarify why the same grounding procedure causes opposite directions of electron flow, yet produces an identical final state for the sphere.