PHYSICS · Multi-part · AP · Physics C: Electricity and Magnetism · Conductors and Capacitors · Conductors and Capacitors
Problem
Two identical conducting spheres, each of charge +6.0μC, are fixed in place and separated by 0.40m. The region between the spheres is first filled with dry air (relative permittivity εr=1.0006) and later completely replaced with a transparent plastic (relative permittivity εr=2.8).
Answer the following questions about the effect of the intervening material on the electrostatic interaction between the spheres.
(a) Describe, in terms of microscopic charge distribution, how the presence of the plastic alters the electric environment between the spheres compared with dry air.
(b) Without performing a numerical calculation, state whether the magnitude of the force between the spheres increases, decreases, or remains essentially the same when the air is replaced by the plastic. Justify your answer qualitatively.
(c) Dry air and plastic both become polarized in an external field, but to very different extents. Explain how differences in molecular structure account for the different relative permittivities given above.