How effective a dielectric is at allowing a capacitor to store more charge depends on the material the dielectric is made from. Every material has a dielectric constant k. This is the ratio of the field without the dielectric (E_o) to the net field (E) with the dielectric:

k

=

Eo E

E is always less than or equal to E_o, so the dielectric constant is greater than or equal to 1. The larger the dielectric constant, the more charge can be stored.

Completely filling the space between capacitor plates with a dielectric increases the capacitance by a factor of the dielectric constant:

C = k C_o, where C_o is the capacitance with no dielectric between the plates.

For a parallel-plate capacitor containing a dielectric that completely fills the space between the plates, the capacitance is given by:

C

=

k eo A d

Capacitance increases as the dielectric constant and the plate area increase, and as the distance between the plates decreases.