TLDR: A capacitor is a device that stores electrical energy by accumulating electric charges on two surfaces that are insulated from each other. It is used in electronic circuits to add capacitance and store energy.

A capacitor is a passive electronic component with two terminals. It is designed to add capacitance to a circuit, which is the ability to store electrical energy. The capacitor consists of two conductors, often in the form of metallic plates, separated by a nonconducting dielectric material. The dielectric acts to increase the capacitor's charge capacity.

There are many different types of capacitors, with varying physical forms and construction. They can be made of materials such as glass, ceramic, plastic film, paper, mica, air, and oxide layers. Capacitors are widely used in electrical circuits in various devices. When a voltage is applied across the terminals of a capacitor, an electric field develops across the dielectric, causing a net positive charge to collect on one plate and a net negative charge to collect on the other plate.

Capacitors have a wide range of applications. They are used in electronic circuits for blocking direct current while allowing alternating current to pass. They are also used in power supplies to smooth the output, in resonant circuits to tune radios to specific frequencies, and in electric power transmission systems to stabilize voltage and power flow. Capacitors were also used as dynamic memory in early digital computers and are still used in modern DRAM.

The history of capacitors dates back to the 18th century when European experimenters discovered that electric charge could be stored in water-filled glass jars, known as Leyden jars. Over time, capacitors evolved with the development of new materials and construction methods. Today, capacitors are an essential component in many electronic devices and play a crucial role in various electrical applications.

In summary, a capacitor is a device that stores electrical energy by accumulating electric charges on two surfaces. It is used in electronic circuits to add capacitance and store energy. Capacitors have a wide range of applications and have evolved over time with advancements in materials and construction methods.