Insulators

Created by Samiksha Sriram Fall 2026

The Main Idea

An insulator is a material that slows down or stops the flow of electricity, heat, or sound. They are typically characterized by their poor conductivity of electromagnetic energy, which sets them apart from both conductors and semiconductors. Insulators contain atoms whose electrons are tightly bound, unlike conductors, which have free electrons. Because the atoms are bound to each other within the mass and cannot be reconfigured through electrochemical manipulation, insulators are characterized as having high resistivity.

Insulating materials, also known as dielectric materials, can exist in all states of matter. Although a perfect ideal insulator would conduct no electricity, all materials conduct electricity to some degree. These insulators can vary in physical characteristics since some materials may be hard/rigid while others can be soft/flexible.

Inductors can also be inside an electric field. Insulators lack free electrons; microscopic dipoles are created via polarization when an external electric field is applied. This internal polarization creates a countering field that only reduces rather than cancels it, and the net electric field inside the inductor is weaker than the external field. Because of this, electric fields exist inside the insulator, whereas inside a conductor, the internal electric field is always zero when at electrostatic equilibrium. Diving deeper into polarization, when it occurs, it causes positive and negative charges to shift or align in opposite directions. This separation creates tiny electric dipoles or aligns molecules that already have permanent dipoles. Overall, the material stays neutral; however, there are distinct positive and negative regions inside the material.

Polarization of an insulated material occurs when molecules with pre-existing dipole moments rotate, or the dipole moments in the individual molecules are induced. This can be seen through the equation D = ε_0​*E+P where D is the electric displacement field, or electric flux density. This value is in the units of C/m^2 and accounts for both free charges and the effect of polarization inside the material. ε_0​ is the permittivity of free space and is a physical constant that represents the value 8.85 x 10^-12 C^2/(N * m^2). This value describes how electric fields behave in a vacuum. E is the electric field and is in the units N/C. Finally, P is the polarization of the medium and represents the value of the dipole moment per unit volume and is in the units C/m^2. Because of this equation, we know that D > ε_0​*E inside the insulating material.

Not all materials polarize equally. Some materials are far more susceptible to polarization than others, and the ratio of the polarization of the medium to ε_0​*E is called the electric susceptibility, χ_e​, of the medium: P = χ_e*​ε_0​*E. Materials that have a larger χ_e​ value are more polarized because their charges are more easily displaced by an external electric field compared to a material with a smaller χ_e​.