The behavior of a dielectric is different for a static and varying electric field and is very much dependent on the frequency.

Static Electric Field:
- In a static electric field, the behavior of a dielectric is characterized by its ability to store electric charge and produce an electric displacement field.
- When a dielectric material is placed in a static electric field, the electric field polarizes the atoms or molecules of the dielectric. The positive charges are displaced in one direction, and the negative charges are displaced in the opposite direction, creating an induced electric dipole moment.
- This dipole moment reduces the overall electric field inside the dielectric, resulting in an increased capacitance of the system.
- The dielectric constant or relative permittivity, represented by the symbol εr, is a measure of how much the capacitance of a capacitor increases when a dielectric is inserted between its plates. It is a constant value for a particular dielectric material in a static electric field.

Varying Electric Field:
- In a varying electric field, such as in an alternating current (AC) circuit, the behavior of a dielectric is more complex.
- When the electric field is varying, the charges in the dielectric are not able to respond instantaneously due to the time required for polarization.
- As the frequency of the varying electric field increases, the charges in the dielectric have less time to respond, and the dielectric material exhibits a reduced ability to store electric charge compared to a static field.
- This frequency-dependent behavior of a dielectric is described by its complex permittivity, represented by the symbol ε*. The complex permittivity has both a real part (ε') and an imaginary part (ε''). The real part represents the dielectric constant in a static field, while the imaginary part represents the dielectric loss or dissipation factor.
- At low frequencies, the dielectric constant dominates, and the behavior of the dielectric is similar to that in a static field.
- At high frequencies, the dielectric loss becomes significant, and the dielectric material may exhibit heating and energy dissipation due to the alternating electric field.

Conclusion:
In summary, the behavior of a dielectric is different for a static electric field and a varying electric field. In a static field, the dielectric constant determines the behavior, while in a varying field, the complex permittivity, which includes the dielectric constant and the dielectric loss, becomes important. The behavior of a dielectric in a varying field is highly dependent on the frequency of the field.