What is a dielectric?

A dielectric is defined as an insulator that is subjected to an electric field. This characteristic allows dielectrics to store electrical energy when a voltage is applied, making them vital components in various electrical and electronic applications, such as capacitors. The presence of the electric field polarizes the dielectric material, which enhances its ability to hold electric charge.

In contrast, a conductor is designed to facilitate the flow of electric current, while a semiconductor is a material that has electrical conductivity between that of insulators and conductors, typically used in transistor and diode technologies. Additionally, a resistor with variable resistance, commonly called a rheostat or potentiometer, is aimed at controlling current flow in circuits rather than exhibiting the properties of storing electrical energy under an electric field. Thus, the identifying feature of a dielectric as an insulator interacting with an electric field clarifies why this is the correct answer.