Relative Dielectric Constant

The factor ε₀ is the dielectric constant of free space and has a value of 8.854 x 10^-12 farads per m in the rationalized MKS system of units. This is also the capacitance of a meter cube of free space when the field is uniform.

The dielectric constant of air and other gaseous dielectrics is slightly higher than that of free space and in nearly all cases this slight difference is neglected. However, the dielectric constant of liquid and solid dielectrics is appreciably greater than that of free space. The ratio of the dielectric constant of a material to that of free space is known as the relative dielectric constant k_r. Therefore, Eq. 2-32 becomes modified to

[2-33]

Typical values of dielectric constants are shown in Table 2-1.

TABLE 2-1. RELATIVE DIELECTRIC CONSTANTS
Material	State	kr	Material	State	kr
Glass	Solid	3.9-5.6	Steatite	Solid	5.9
Isolantite	Solid	3.8	Pyranol	Liquid	5.3
Mica	Solid	5.45	Oil	Liquid	2.2
Polyethelene	Solid	2.25	Water	Liquid	78.0
Polystyrene	Solid	2.25	Air	Gas	1.00009
Quartz	Solid	3.9	C02	Gas	1.000985
Paper	Solid	3.5	H2	Gas	1.000264

Liquid and solid dielectrics have higher dielectric constants than free space because of an orientation of electric dipoles, a phenomenon known as dielectric polarization, and explained in Section 2-22.