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capacitance
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What is capacitance?
Capacitance is the property of an electrical conductor or a set of conductors that measures the amount of separated electric charge stored per unit change in electrical potential. This property also implies the storage of electrical energy. The unit of capacitance is the farad (F), named after Michael Faraday, where one farad is equal to one coulomb per volt.
A capacitor, also known as a condenser, is a device designed to store electrical energy. It typically consists of two conductors separated by an insulating material called a dielectric. Capacitors are crucial in various applications, including digital circuits for memory backup during power interruptions and as filters to protect sensitive components from electrical surges. The amount of charge a capacitor can store depends on the area of its plates, the distance between them, the type of dielectric material used, and the applied voltage.
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What is a capacitor used for in electronics?
A capacitor is an electronic component used for storing electrical energy. It consists of two conductors separated by an insulator. Capacitors have crucial applications in electronics, such as maintaining information in computer memories during brief power outages. They also function as filters, protecting sensitive circuits from damage caused by electrical surges by diverting unwanted signals. The energy stored in a capacitor is held within the electric field between its plates.
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How does a capacitor store electrical charge?
A capacitor stores electrical charge using two conductors separated by an insulator, known as a dielectric. When a voltage is applied, positive charge accumulates on one conductor and negative charge on the other. This separation of charge creates an electric field between the conductors. The energy required to establish this field is stored within the capacitor. The amount of charge a capacitor can store is determined by its capacitance, which depends on the area of the conductors, the distance between them, and the properties of the dielectric material.
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What is the unit of capacitance?
The unit of capacitance is the farad (F). It is named after the English scientist Michael Faraday. One farad is defined as the capacitance of a capacitor where one coulomb of electric charge changes the potential difference between its plates by one volt.
In practice, the farad is a very large unit. Capacitors are typically rated in smaller units such as microfarads (μF), where 1 μF = 10-6 F, or picofarads (pF), where 1 pF = 10-12 F. Capacitance is the ability of a conductor or set of conductors to store separated electric charge per unit change in electrical potential, and it is associated with the storage of electrical energy.
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How do the size and materials of a capacitor affect its capacitance?
The capacitance of a capacitor is influenced by its size and the materials used. For a parallel-plate capacitor, increasing the area of the plates (A) and decreasing the distance (d) between them will increase its capacitance. The formula for a parallel-plate capacitor is (C = \epsilon_0 \kappa A / d), where (C) is capacitance, (\epsilon_0) is the permittivity of free space, (\kappa) is the dielectric constant of the material between the plates, (A) is the area of the plates, and (d) is the distance between them.
The material inserted between the conductors, known as a dielectric, also significantly affects capacitance. A dielectric material has a dielectric constant ((\kappa)) greater than one. When a dielectric is used, it reduces the electric field and potential difference for a given charge, thereby increasing the capacitor's ability to store charge. Materials with higher dielectric constants, such as barium titanate, result in higher capacitance compared to materials with lower dielectric constants like air or vacuum.
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What are some practical uses of capacitors in everyday electronic devices?
Capacitors serve crucial roles in everyday electronics by storing electrical energy. They are vital in digital circuits, particularly in computer memories, to retain information during brief power interruptions. Additionally, capacitors function as filters, diverting harmful electrical surges and protecting sensitive components and circuits from damage.
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capacitance, property of an electric conductor, or set of conductors, that is measured by the amount of separated electric charge that can be stored on it per unit change in electrical potential. Capacitance also implies an associated storage of electrical energy. If electric charge is transferred between two initially uncharged conductors, both become equally charged, one positively, the other negatively, and a potential difference is established between them. The capacitance C is the ratio of the amount of charge q on either conductor to the potential difference V between the conductors, or simply C = q/V.
In both the practical and the metre–kilogram–second scientific systems, the unit of electric charge is the coulomb and the unit of potential difference is the volt, so that the unit of capacitance—named the farad (symbolized F)—is one coulomb per volt. One farad is an extremely large capacitance. Convenient subdivisions in common use are one-millionth of a farad, called a microfarad (μF), and one-millionth of a microfarad, called a picofarad (pF; older term, micromicrofarad, μμF). In the electrostatic system of units, capacitance has dimensions of distance.
Capacitance in electric circuits is deliberately introduced by a device called a capacitor. It was discovered by the Prussian scientist Ewald Georg von Kleist in 1745 and independently by the Dutch physicist Pieter van Musschenbroek at about the same time, while in the process of investigating electrostatic phenomena. They discovered that electricity obtained from an electrostatic machine could be stored for a period of time and then released. The device, which came to be known as the Leyden jar, consisted of a stoppered glass vial or jar filled with water, with a nail piercing the stopper and dipping into the water. By holding the jar in the hand and touching the nail to the conductor of an electrostatic machine, they found that a shock could be obtained from the nail after disconnecting it, by touching it with the free hand. This reaction showed that some of the electricity from the machine had been stored.
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A simple but fundamental step in the evolution of the capacitor was taken by the English astronomer John Bevis in 1747 when he replaced the water by metal foil forming a lining on the inside surface of the glass and another covering the outside surface. This form of the capacitor with a conductor projecting from the mouth of the jar and touching the lining had, as its principal physical features, two conductors of extended area kept nearly equally separated by an insulating, or dielectric, layer made as thin as practicable. These features have been retained in every modern form of capacitor.
A capacitor, also called a condenser, is thus essentially a sandwich of two plates of conducting material separated by an insulating material, or dielectric. Its primary function is to store electrical energy. Capacitors differ in the size and geometrical arrangement of the plates and in the kind of dielectric material used. Hence, they have such names as mica, paper, ceramic, air, and electrolytic capacitors. Their capacitance may be fixed or adjustable over a range of values for use in tuning circuits.
The energy stored by a capacitor corresponds to the work performed (by a battery, for example) in creating opposite charges on the two plates at the applied voltage. The amount of charge that can be stored depends on the area of the plates, the spacing between them, the dielectric material in the space, and the applied voltage.
A capacitor incorporated in an alternating-current (AC) circuit is alternately charged and discharged each half cycle. The time available for charging or discharging thus depends on the frequency of the current, and if the time required is greater than the length of the half cycle, the polarization (separation of charge) is not complete. Under such conditions, the dielectric constant appears to be less than that observed in a direct-current circuit and to vary with frequency, becoming lower at higher frequencies. During the alternation of polarity of the plates, the charges must be displaced through the dielectric first in one direction and then in the other, and overcoming the opposition that they encounter leads to a production of heat known as dielectric loss, a characteristic that must be considered when applying capacitors to electrical circuits, such as those in radio and television receivers. Dielectric losses depend on frequency and the dielectric material.
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Except for the leakage (usually small) through the dielectric, no current flows through a capacitor when it is subject to a constant voltage. Alternating current will pass readily, however, and is called a displacement current.