Electrical capacitor
Passive component storing electrical energy via separated conductors.
A capacitor is a passive electronic component with two terminals. It stores electrical energy by holding electric charges on two surfaces that are close together but kept apart by an insulator. The device was originally called a condenser—a term that still appears in a few compound names, like the condenser microphone—and is sometimes informally referred to as a cap.
How useful a capacitor is depends on its capacitance. While any two nearby electrical conductors in a circuit have some natural capacitance, a capacitor is built specifically to add capacitance to a part of the circuit. Practical capacitors come in many shapes and sizes. Most contain at least two electrical conductors—often metal plates, foils, thin films, sintered metal beads, or electrolytes—separated by a nonconducting dielectric material. Common dielectrics include glass, ceramic, plastic film, paper, mica, air, and oxide layers. When a voltage is applied across the terminals, an electric field forms in the dielectric, causing a net positive charge on one plate and a net negative charge on the other. No current flows through a perfect dielectric, but charge does flow in the source circuit. If the voltage is steady, that flow eventually stops. If the voltage changes over time, the source experiences ongoing current as the capacitor charges and discharges.
Capacitors are used in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy, though real ones lose a small amount. In circuits, they block direct current while letting alternating current pass. They smooth the output of power supplies in analog filter networks, tune radios to specific frequencies in resonant circuits, and stabilize voltage and power flow in electric power transmission systems. Early digital computers used capacitors for dynamic memory, and modern DRAM still does. A natural example of capacitance is the static charge between clouds and the Earth’s surface, with air acting as the dielectric; lightning occurs when the air’s breakdown voltage is exceeded.
The earliest capacitors appeared in the 1740s. In October 1745, Ewald Georg von Kleist in Pomerania, Germany, discovered that charge could be stored by connecting a high-voltage electrostatic generator to water in a hand-held glass jar. His hand and the water acted as conductors, and the jar as the dielectric. Touching the wire prod
- field
- Electrical engineering, electronics
- known_for
- Storing electrical energy as an electric field between conductors separated by a dielectric
- first_created
- 1740s
- earliest_form
- Leyden jar (water-filled glass jar)
Lore & Background
The earliest forms of capacitors were created in the 1740s, when European experimenters discovered that electric charge could be stored in water-filled glass jars that came to be known as Leyden jars. In October 1745, Ewald Georg von Kleist of Pomerania, Germany, found that charge could be stored by connecting a high-voltage electrostatic generator by a wire to a volume of water in a hand-held glass jar. Von Kleist found that touching the wire resulted in a powerful spark. The following year, the Dutch physicist Pieter van Musschenbroek invented a similar capacitor, which was named the Leyden jar, after the University of Leiden where he worked.
Benjamin Franklin investigated the Leyden jar and concluded that the charge was stored on the glass, not in the water. He also adopted the term 'battery'. In 1747, Leyden jars were made by coating the inside and outside of jars with metal foil. The earliest unit of capacitance was the jar, equivalent to about 1.11 nanofarads. Leyden jars or devices employing flat glass plates alternating with foil conductors were used exclusively until about 1900, when the invention of wireless radio created a demand for standard capacitors with lower inductance. More compact construction methods began to be used, such as a flexible dielectric sheet sandwiched between sheets of metal foil, rolled or folded into a small package.
Reader's Guide
Capacitors are fundamental components in modern electronics, with utility depending on their capacitance. They are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy, although real-life capacitors do dissipate a small amount. In analog filter networks, they smooth the output of power supplies. In resonant circuits they tune radios to particular frequencies. In electric power transmission systems, they stabilize voltage and power flow. The property of energy storage in capacitors was exploited as dynamic memory in early digital computers, and still is in modern DRAM. The MOS capacitor was later widely adopted as a storage capacitor in memory chips and as the basic building block of the charge-coupled device (CCD) in image sensor technology. The most common example of natural capacitance are the static charges accumulated between clouds and the Earth's surface, where the air serves as the dielectric, resulting in lightning when the breakdown voltage of air is exceeded.
Did You Know?
- The earliest forms of capacitors were created in the 1740s and were known as Leyden jars.
- Benjamin Franklin concluded that charge in a Leyden jar was stored on the glass, not in the water.
- The term 'condenser' was used by Alessandro Volta in 1780 and was deprecated in favor of 'capacitor' recommended by the British Engineering Standards Association in 1926.
- Electric double-layer capacitors (supercapacitors) were invented in 1957 by H. Becker.
More in Dutch inventions 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record