Insulators are materials in which the internal charge cannot flow freely and thus cannot conduct electric current to an appreciable degree when exposed to an electric field.

While there is no perfect insulator with infinite resistivity, materials like glass, paper and Teflon have very high resistivity and can effectively serve as insulators in most instances. Just as conductors are used to carrying electrical current through wires, insulators are commonly used as a coating for the wires.

Insulators, like conductors, have their physical limits. When exposed to enough voltage, an insulator will experience what is known as an electrical breakdown, in which current suddenly spikes through the material as it becomes a conductor.

A dielectric is an insulator that can be polarized by an electric field, meaning that it is a material in which charge does not flow freely, but in the presence of an electric field, it can shift its charge distribution. The positive charge in a dielectric will migrate towards the negative side of the applied field, while negative charges will shift the other way. This creates a weak local field within the material that opposes the applied field. Different materials will react differently to an induced field, depending on their dielectric constant. This constant is the degree of their polarizability (the extent to which they become polarized).

 

Practice Questions

 

MCAT Official Prep (AAMC)

Chemistry Online Flashcards Question 10

 

Key Points

• Insulators are materials in which the internal charge cannot flow freely and thus cannot conduct electric current to an appreciable degree when exposed to an electric field.

• Dielectric is an insulating material. With a constant k specific to each type of material.

Key Terms

Insulator: a substance that does not transmit heat (thermal insulator), sound (acoustic insulator) or electricity (electrical insulator).

Dielectric: insulating material or a very poor conductor of electric current

Resistivity is a measure of the resistance of a given size of a specific material to electrical conduction

Conductor: a material which contains movable electric charges

Current: the rate of flow of electric charge past a point or region

Voltage: an electromotive force or potential difference expressed in volts

Electric field: a region around a charged particle or object within which a force would be exerted on other charged particles or objects