A long, solid plastic rod of radius 1.0 cm is uniformly charged with positive charge…
PHYSICS · Multi-part · AP · Physics C: Electricity and Magnetism · Conductors and Capacitors · Conductors and Capacitors
Problem
A long, solid plastic rod of radius 1.0 cm is uniformly charged with positive charge throughout its volume. A small spherical cavity of radius 0.25 cm is then introduced entirely within the rod, with the center of the cavity located 0.50 cm from the rod’s central axis. Afterward, the rod is left undisturbed for a long time so that charges can reach equilibrium.
In a separate experiment, an identical cavity is drilled at the same location in an otherwise identical solid metal rod that is given the same total positive charge.
(a) Describe qualitatively the electric field at points inside the cavity in the plastic rod. Include in your discussion the expected direction and whether the magnitude is uniform, non-uniform, or zero.
(b) Describe qualitatively the electric field at points inside the cavity in the metal rod. Explain how the metal’s charge distribution leads to this result.
(c) Suppose a small neutral conducting sphere is now inserted into the cavity of the plastic rod without touching its walls. Predict whether this sphere will acquire a net charge and/or experience an electric force. Justify your prediction based on the field you described in part (a).
(d) Summarize the fundamental differences between insulators and conductors that lead to the contrasting behaviors you have discussed in parts (a)–(c).