A capacitor is a passive electronic component that stores electrical charge. The amount of energy a capacitor can store is known as capacitance, measured in farads (F). Capacitors are found in almost every electronic circuit and serve various essential functions.

Capacitors can store small amounts of electrical energy, similar to a rechargeable battery, although they hold much less energy compared to batteries of the same size and weight. Supercapacitors, a special type, can hold more energy than regular capacitors but still less than most batteries. However, capacitors can be charged and discharged extremely quickly, sometimes millions of times per second.

The basic structure of a capacitor consists of two conductors (such as metal plates) separated by an insulator called a dielectric. When voltage is applied, one plate accumulates positive charge and the other accumulates negative charge, with the dielectric material preventing direct electron flow between them. This arrangement lets capacitors store and release electrical energy efficiently.

A capacitor’s capacity to store charge depends on three primary factors: the surface area of its plates, the distance between them, and the properties of the dielectric. Different types of capacitors include ceramic, film, electrolytic, and supercapacitors, each with unique use cases. Over time, capacitors may fail, especially those containing liquid electrolytes, and this is a common cause of malfunction in electronic devices – bulging or leaking capacitors often need replacement.

How Do Capacitors Work?

Capacitors function by momentarily storing and releasing electrical charge. When a circuit applies voltage, electrons accumulate on one plate, building up a separated electrical potential. Once full, no more current can enter. When the circuit calls for it, the capacitor discharges its stored energy, releasing it rapidly.

Early capacitors used foil and paper. Modern designs use ceramics, polymers, or even etching directly onto integrated circuits. Most capacitors used in electronics are rated in microfarads, nanofarads, or picofarads, while supercapacitors can store tens of farads.

What Are Capacitors Used For?

Capacitors are critical components in almost every electronic device:

• Energy smoothing: They keep electrical flows steady, for example in converting alternating current to direct current.
• Noise filtering: Capacitors remove unwanted signals or interference from circuits, protecting sensitive components.
• Frequency tuning: By combining with inductors, capacitors can create filters that select or block specific frequencies, which is essential in radio and communication devices.
• Data storage: Capacitors paired with transistors are key to devices like dynamic RAM, where each stores a bit of data for a brief period.
• Sensing: Capacitors are used in touchscreens and light sensors, utilizing their ability to detect changes in charge.

Even after a device is powered off, capacitors can retain a charge, so caution is necessary when working with electronics. From power supplies to communications equipment and digital memory, capacitors are fundamental to modern technology.