A dielectric is a nonconducting material, such as rubber, glass, or waxed paper. When
a dielectric is inserted between the plates of a capacitor, the capacitance increases. If
the dielectric completely fills the space between the plates, the capacitance increases
by a dimensionless factor 1, which is called the dielectric constant of the material.
The dielectric constant varies from one material to another. In this section, we analyze
this change in capacitance in terms of electrical parameters such as electric charge,
electric field, and potential difference; in Section 26.7, we shall discuss the microscopic
origin of these changes.