Relative dielectric constant is the basic information necessary for designing capacitors. If we want to use a new material in our circuit, maybe this new material will introduce capacitance, so we must know the relative dielectric constant of the new material. If a material with high relative dielectric constant is placed in an electric field, the field strength in the dielectric will decrease significantly. This fact is often used to increase the capacitance of a particular capacitor design. The dielectric layer under the conductor etched by the printed wiring board (PWB) can be used for insulation.

Dielectric is also used for RF transmission lines. In coaxial cable, dielectric polyethylene can be used to isolate the middle conductor and shield the outer layer. It can also be placed in the middle of the waveguide to form a dielectric waveguide. Dielectric waveguides are rarely used, because the dielectric loss of all known dielectric materials is too large for effective transmission of electromagnetic fields, but they can be used in special applications, such as filters.

Scientists deliberately doped impurities into optical fibers. In this way, the exact value of εr in the cross section can be controlled very advantageously. This will control the reflection coefficient of the material, thus controlling the mode of light transmission. Doped optical fibers can also be used to form optical amplifiers.