PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Electric Force Field and Potential · Electric Force Field and Potential
Problem
A student observes that when a small, lightweight piece of paper is initially brought near a negatively charged plastic rod, the paper is first attracted to the rod, briefly touches it, and then is repelled away.
Use the observations to analyze how charge redistribution within the paper explains the sequence of forces that act on the paper. Assume the paper was electrically neutral before the experiment began.
(a) Describe qualitatively how the distribution of charge within the neutral paper changes as the negatively charged rod is brought close but has not yet touched the paper.
(b) Explain why an attractive force arises between the rod and the paper during the interval described in part (a).
(c) After the paper briefly contacts the rod, the paper is observed to be repelled. Explain the mechanism by which the paper acquires a net charge during the contact and why this results in a repulsive force once the paper leaves the rod.
(d) The student claims that total electric charge was conserved during the entire process. Cite specific evidence from the observations and your explanations in parts (a)–(c) that supports or refutes the student’s claim.