8.1.C—Describe the electric permittivity of a material or medium

Describe the electric permittivity of a material or medium.

• Electric permittivity is a measurement of the degree to which a material or medium is polarized in the presence of an electric field.
• Electric polarization can be modeled as the induced rearrangement of electrons by an external electric field, resulting in a separation of positive and negative charges within a material or medium.
• Free space has a constant value of electric permittivity, , that appears in physical relationships.
• The permittivity of matter has a value different from that of free space that arises from the matter’s composition and arrangement.
  • i. In a given material, electric permittivity is determined by the ease with which electrons can change configurations within the material.
  • ii. Conductors are made from electrically conducting materials in which charge carriers move easily; insulators are made from electrically nonconducting materials in which charge carriers cannot move easily. BOUNDARY STATEMENT AP Physics C: Electricity & Magnetism only expects students to make calculations of the electric force between four or fewer interacting charged objects or systems. The analysis of the resulting electric force from more charges is allowed in situations of high symmetry. Note that students are expected to calculate the electric fields of charge distributions, as described in Topics 8.4 and 8.6.