A negatively charged plastic rod is slowly brought to within a few millimeters of…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A negatively charged plastic rod is slowly brought to within a few millimeters of several small, initially neutral objects resting on an insulating table: a torn fragment of copier paper, a chip of dry wood, and a square of aluminum foil. All three objects experience an attractive force toward the rod.
Answer the following about the physical origin and relative strength of that attraction.
(a) Describe the microscopic rearrangement of charge that occurs inside any one of the neutral objects as the rod approaches. Your explanation should explicitly reference the motion or displacement of electrons and the resulting spatial distribution of charge within the object.
(b) Using your description from part (a), explain why the net electrostatic force on the object points toward the rod even though the object remains overall electrically neutral.
(c) Rank the magnitude of the attractive force exerted on the three objects (copier-paper fragment, dry wood chip, aluminum foil square) from greatest to least, and justify your ranking in terms of material properties relevant to charge motion or polarization.