What device consists of a pair of metallic plates separated by an insulating material called a dielectric?

A device that consists of a pair of metallic plates separated by an insulating material known as a dielectric is called a capacitor. Capacitors play a crucial role in electrical circuits and are used for storing electrical energy temporarily. The metallic plates, often made from conductive materials, allow the capacitor to hold charge, while the dielectric material, which can be made from various materials such as ceramic, plastic, or glass, serves to increase the capacitor's ability to store electrical energy while also preventing the plates from touching each other, which would create a short circuit.

The concept of capacitance is rooted in the relationship between the stored charge and the voltage across the plates. When a voltage is applied to the capacitor, an electric field develops across the dielectric, allowing the device to store energy that can be used later in the circuit.

In the context of the other choices, a storage battery is designed to store energy in a different manner, usually through electrochemical reactions; a voltage regulator is responsible for maintaining a constant voltage level; and a rectifier converts alternating current (AC) to direct current (DC). These devices operate on different principles and constructions, making them distinct from the fundamental design and function of a capacitor.