NationMaster - Encyclopedia: Capacitance

Capacitance is a measure of the amount of electric charge stored (or separated) for a given electric potential. Image File history File links Solenoid. ... Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge and magnetic charge, and is in turn affected by the presence and motion of those particles. ... Lightning strikes during a night-time thunderstorm. ... Magnetic lines of force of a bar magnet shown by iron filings on paper In physics, magnetism is one of the phenomena by which materials exert an attractive or repulsive force on other materials. ... Electrostatics (also known as Static Electricity) is the branch of physics that deals with the forces exerted by a static (i. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... Coulombs torsion balance In physics, Coulombs law is an inverse-square law indicating the magnitude and direction of electrostatic force that one stationary, electrically charged object of small dimensions (ideally, a point source) exerts on another. ... It has been suggested that optical field be merged into this article or section. ... In physics and mathematical analysis, Gausss law, closely related to Gausss theorem, gives the relation between the electric or gravitational flux flowing out of a closed surface and, respectively, the electric charge or mass enclosed in the surface. ... This article or section does not cite any references or sources. ... In physics, the electric dipole moment for a pair of opposite charges of magnitude q is defined as the magnitude of the charge times the distance between them and the defined direction is toward the positive charge. ... This article needs to be cleaned up to conform to a higher standard of quality. ... An electric current produces a magnetic field. ... In physics, a magnetic field is a force field that surrounds electric current circuits. ... A bar magnet. ... Classical electrodynamics (or classical electromagnetism) is a theory of electromagnetism that was developed over the course of the 19th century, most prominently by James Clerk Maxwell. ... Electric current is the flow (movement) of electric charge. ... In physics, the Lorentz force is the force exerted on a charged particle in an electromagnetic field. ... Electromotive force (emf) is the amount of energy gained per unit charge that passes through a device in the opposite direction to the electric field existing across that device. ... Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic flux. ... Faradays law of induction (more generally, the law of electromagnetic induction) states that the induced emf (electromotive force) in a closed loop equals the negative of the time rate of change of magnetic flux through the loop. ... Displacement current is a quantity related to a changing electric field. ... In electromagnetism, Maxwells equations are a set of equations first presented as a distinct group in the later half of the nineteenth century by James Clerk Maxwell. ... The electromagnetic field is a physical field that is produced by electrically charged objects and which affects the behaviour of charged objects in the vicinity of the field. ... It has been suggested that this article or section be merged with light. ... This article or section does not adequately cite its references or sources. ... Electrical conduction is the movement of electrically charged particles through a transmission medium (electrical conductor). ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... Inductance (or electric inductance) is a measure of the amount of magnetic flux produced for a given electric current. ... Electrical impedance, or simply impedance, is a measure of opposition to a sinusoidal alternating electric current. ... A resonator is a device or part that vibrates (or oscillates) with waves. ... It has been suggested that this article or section be merged with Waveguide (optics). ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... This article or section does not cite any references or sources. ...

In a capacitor, there are two conducting electrodes which are insulated from one another. The charge on the electrodes is +Q and -Q, and V represents the potential difference between the electrodes. The SI unit of capacitance is the farad; 1 farad = 1 coulomb per volt. Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. ... Look up si, Si, SI in Wiktionary, the free dictionary. ... Examples of various types of capacitors. ... The coulomb (symbol: C) is the SI unit of electric charge. ... Josephson junction array chip developed by NIST as a standard volt. ...

Capacitors

The capacitance of the majority of capacitors used in electronic circuits is several orders of magnitude smaller than the farad. The most common units of capacitance in use today are the millifarad (mF), microfarad (µF), the nanofarad (nF) and the picofarad (pF) Examples of various types of capacitors. ... The term microfarad is used to note the storage capacity value of electrolytic capacitors and represents one millionth of a farad, or 0. ... The nanofarad (symbol nF) is a submultiple of the SI unit of electrical capacitance, the farad. ... The picofarad (pronounced or ) is the smallest measurable unit of electrical capacitance. ...

The capacitance can be calculated if the geometry of the conductors and the dielectric properties of the insulator between the conductors are known. For example, the capacitance of a parallel-plate capacitor constructed of two parallel plane electrodes of area A separated by a distance d is approximately equal to the following: Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. ...

The equation is a good approximation if d is small compared to the other dimensions of the electrodes. The farad (symbol F) is the SI unit of capacitance (named after Michael Faraday). ... Permittivity is a physical quantity that describes how an electric field affects and is affected by a dielectric medium and is determined by the ability of a material to polarize in response to an applied electric field, and thereby to cancel, partially, the field inside the material. ... In science, a physical constant is a physical quantity whose numerical value does not change. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... The or meter (see spelling differences) is a measure of length. ...

The dielectric constant for a number of very useful dielectrics changes as a function of the applied electrical field, e.g. ferroelectric materials, so the capacitance for these devices is no longer purely a function of device geometry. If a capacitor is driven with a sinusoidal voltage, the dielectric constant, or more accurately referred to as the dielectric permittivity, is a function of frequency. A changing dielectric constant with frequency is referred to as a dielectric dispersion, and is governed by dielectric relaxation processes, such as Debye relaxation. In physics, the ferroelectric effect is an electrical phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment. ... Because polarization cannot follow an electric field in a high-frequency field, permittivity has a dependence on the frequency. ... In physics, dielectric relaxation refers to the relaxation reponse of a dielectric medium to an external field of microwave frequencies. ... Debye relaxation is the dielectric relaxation response of an ideal, noninteracting population of dipoles to an alternating external electric field. ...

Energy

The energy (measured in joules) stored in a capacitor is equal to the work done to charge it. Consider a capacitance C, holding a charge +q on one plate and -q on the other. Moving a small element of charge

d q

from one plate to the other against the potential difference V = q/C requires the work

d W

: The joule (IPA pronunciation: or ) (symbol: J) is the SI unit of energy. ...

We can find the energy stored in a capacitance by integrating this equation. Starting with an uncharged capacitance (q=0) and moving charge from one plate to the other until the plates have charge +Q and -Q requires the work W: The joule (IPA pronunciation: or ) (symbol: J) is the SI unit of energy. ... The coulomb (symbol: C) is the SI unit of electric charge. ... In calculus, the integral of a function is an extension of the concept of a sum. ...

Combining this with the above equation for the capacitance of a flat-plate capacitor, we get:

The joule (IPA pronunciation: or ) (symbol: J) is the SI unit of energy. ... Josephson junction array chip developed by NIST as a standard volt. ...

Capacitance and 'displacement current'

The physicist James Clerk Maxwell invented the concept of displacement current, $frac{partial vec{D}}{partial t}$ , to make Ampère's law consistent with conservation of charge in cases where charge is accumulating, for example in a capacitor. He interpreted this as a real motion of charges, even in vacuum, where he supposed that it corresponded to motion of dipole charges in the ether. Although this interpretation has been abandoned, Maxwell's correction to Ampère's law remains valid (a changing electric field produces a magnetic field). James Clerk Maxwell (13 June 1831 â€“ 5 November 1879) was a Scottish mathematician and theoretical physicist. ... Displacement current is a quantity related to a changing electric field. ... An electric current produces a magnetic field. ... Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. ... The Earths magnetic field, which is approximately a dipole. ... Chinese Wood (æœ¨) | Fire (ç«) | Earth (åœŸ) | Metal (é‡‘) | Water (æ°´) Hinduism and Buddhism The Pancha Mahabhuta (The Five Great Elements) Vayu/Pavan (Air/Wind) Agni/Tejas (Fire) Akasha (Aether) Prithvi/Bhumi (Earth) Ap/Jala (Water) Aether (also spelled ether) is a concept used in ancient and medieval science as a substance. ... An electric current produces a magnetic field. ...

Maxwell's equation combining Ampère's law with the displacement current concept is given as $vec{nabla} times vec{H} = vec{J} + frac{partial vec{D}}{partial t}$ . (Integrating both sides, the integral of $vec{nabla}times vec{H}$ can be replaced — courtesy of Stokes's theorem — with the integral of $vec{H} cdot mathrm{d} vec{l}$ over a closed contour, thus demonstrating the interconnection with Ampère's formulation.) Stokes theorem in differential geometry is a statement about the integration of differential forms which generalizes several theorems from vector calculus. ...

Capacitance/inductance duality

In mathematical terms, the ideal capacitance can be considered as an inverse of the ideal inductance, because the voltage-current equations of the two phenomena can be transformed into one another by exchanging the voltage and current terms. Inductance (or electric inductance) is a measure of the amount of magnetic flux produced for a given electric current. ...

Self-capacitance

In electrical circuits, the term capacitance is usually a shorthand for the mutual capacitance between two adjacent conductors, such as the two plates of a capacitor. There also exists a property called self-capacitance, which is the amount of electrical charge that must be added to an isolated conductor to raise its electrical potential by one volt. The reference point for this potential is a theoretical hollow conducting sphere, of infinite radius, centred on the conductor. Using this method, the self-capacitance of a conducting sphere of radius R is given by: Mutual capacitance is intentional or unintentional capacitance that occurs between two charge-holding objects or conductors, in which the current passing through one passes over into the other. ...

Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ...

Elastance

The inverse of capacitance is called elastance, and its unit is the reciprocal farad, also informally called the daraf. Electrical elastance is the inverse of capacitance. ... The daraf is the unit of electrical elastance (symbol: F-1), the ability of an electric potential to charge a capacitor; it is the reciprocal of the farad. ...

Stray capacitance

Any two adjacent conductors can be considered as a capacitor, although the capacitance will be small unless the conductors are close together or long. This (unwanted) effect is termed "stray capacitance". Stray capacitance can allow signals to leak between otherwise isolated circuits (an effect called crosstalk), and it can be a limiting factor for proper functioning of circuits at high frequency. Look up crosstalk in Wiktionary, the free dictionary. ... High frequency (HF) radio frequencies are between 3 and 30 MHz. ...

Stray capacitance is often encountered in amplifier circuits in the form of "feedthrough" capacitance that interconnects the input and output nodes (both defined relative to a common ground). It is often convenient for analytical purposes to replace this capacitance with a combination of one input-to-ground capacitance and one output-to-ground capacitance. (The original configuration — including the input-to-output capacitance — is often referred to as a pi-configuration.) Miller's theorem can be used to effect this replacement. Miller's theorem states that, if the gain ratio of two nodes is 1:K, then an impedance of Z connecting the two nodes can be replaced with a Z/(1-k) impedance between the first node and ground and a KZ/(K-1) impedance between the second node and ground. (Since impedance varies inversely with capacitance, the internode capacitance, C, will be seen to have been replaced by a capacitance of KC from input to ground and a capacitance of (K-1)C/K from output to ground.) When the input-to-output gain is very large, the equivalent input-to-ground impedance is very small while the output-to-ground impedance is essentially equal to the original (input-to-output) impedance. In electronics, the Miller effect describes the fact that a capacitance between input and output of an amplifier is multiplied by a factor of , where is the voltage gain of the amplifier. ... Electrical impedance, or simply impedance, is a measure of opposition to a sinusoidal alternating electric current. ...

Footnotes

References

External links

Contents