The unit is named after Ernst Werner von Siemens. In English, the same word siemens is used both for the singular and plural.[3] Like other SI units named after people, the symbol (S) is capitalized but the name of the unit is not. For the siemens this distinguishes it from the second, symbol (lower case) s.
The related property, electrical conductivity, is measured in units of siemens per metre (S/m).
where I is the electric current through the object and V is the voltage (electrical potential difference) across the object.
The unit siemens for the conductanceG is defined by
where Ω is the ohm, A is the ampere, and V is the volt.
For a device with a conductance of one siemens, the electric current through the device will increase by one ampere for every increase of one volt of electric potential difference across the device.
The conductance of a resistor with a resistance of five ohms, for example, is (5Ω)−1, which is equal to 200mS.
A historical equivalent for the siemens is the mho (/ˈmoʊ/). The name is derived from the word ohm spelled backwards as the reciprocal of one ohm, at the suggestion of Sir William Thomson (Lord Kelvin) in 1883.[4] Its symbol is an inverted capital Greek letter omega: U+2127℧INVERTED OHM SIGN.
NIST's Guide for the Use of the International System of Units (SI) refers to the mho as an "unaccepted special name for an SI unit", and indicates that it should be strictly avoided.[5]
The SI term siemens is used universally in science and often in electrical applications, while mho is still used in some electronic contexts.[6][7]
The inverted capital omega symbol (℧), while not an official SI abbreviation, is less likely to be confused with a variable than the letter "S" when writing the symbol by hand. The usual typographical distinctions (such as italic for variables and roman for units) are difficult to maintain. Likewise, it is difficult to distinguish the symbol "S" (siemens) from the lower-case "s" (seconds), potentially causing confusion.[8] So, for example, a pentode’s transconductance of 2.2mS might alternatively be written as 2.2m℧ or 2200μ℧ (most common in the 1930s) or 2.2mA/V.
The ohm had officially replaced the old "siemens unit", a unit of resistance, at an international conference in 1881.[9]
Notes and references
↑ Minutes(PDF). 14th General Conference on Weights and Measures. 1971. p.53.
↑ Minutes(PDF). 14th General Conference on Weights and Measures. 1971. p.78.
↑ Thomson, William (1884). "Electrical Units of Measurement". The Practical Applications of Electricity. Institution of Civil Engineers. pp.149–174 at p 171 (Lecture given 3 May 1883). Available online. Thomson helpfully added that the proper pronunciation of "mho" could be obtained by taking a phonograph and turn it backwards.
↑ "Chapter 5: Units Outside the SI". NIST Guide to the SI (Report). National Institute of Standards and Technology. 2008. Retrieved 2017-12-22.
↑ Al Dahaan, S., Al-Ansari, N., & Knutsson, S. (2016). Influence of groundwater hypothetical salts on electrical conductivity total dissolved solids. Engineering, 8(11), 823-830.
↑ SINGH, S., GAUTAM, P. K., KUMAR, P., BISWAS, A., & SARKAR, T. (2021). Delineating the characteristics of saline water intrusion in the coastal aquifers of Tamil Nadu, India by analysing the Dar-Zarrouk parameters. Contributions to Geophysics & Geodesy, 51(2).
↑ Weiner, Eugene R. (2013). Applications of Environmental Aquatic Chemistry: A practical guide. CRC Press. p.109. ISBN978-1439853320.
The ampere, often shortened to amp, is the unit of electric current in the International System of Units (SI). One ampere is equal to 1 coulomb (C) moving past a point in 1 second. It is named after French mathematician and physicist André-Marie Ampère (1775–1836), considered the father of electromagnetism along with Danish physicist Hans Christian Ørsted.
The volt is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI).
In electrical engineering, impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit.
The coulomb (symbol: C) is the unit of electric charge in the International System of Units (SI). It is equal to the electric charge delivered by a 1 ampere current in 1 second and is defined in terms of the elementary charge e, at about 6.241509×1018e.
Ohm's law states that the electric current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the three mathematical equations used to describe this relationship:
The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is electrical conductance, measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with mechanical friction. The SI unit of electrical resistance is the ohm, while electrical conductance is measured in siemens (S).
The henry is the unit of electrical inductance in the International System of Units (SI). If a current of 1 ampere flowing through a coil produces flux linkage of 1 weber turn, that coil has a self inductance of 1 henry. The unit is named after Joseph Henry (1797–1878), the American scientist who discovered electromagnetic induction independently of and at about the same time as Michael Faraday (1791–1867) in England.
The farad (symbol: F) is the unit of electrical capacitance, the ability of a body to store an electrical charge, in the International System of Units (SI), equivalent to 1 coulomb per volt (C/V). It is named after the English physicist Michael Faraday (1791–1867). In SI base units 1 F = 1 kg−1⋅m−2⋅s4⋅A2.
In electrical engineering, admittance is a measure of how easily a circuit or device will allow a current to flow. It is defined as the reciprocal of impedance, analogous to how conductance and resistance are defined. The SI unit of admittance is the siemens ; the older, synonymous unit is mho, and its symbol is ℧. Oliver Heaviside coined the term admittance in December 1887. Heaviside used Y to represent the magnitude of admittance, but it quickly became the conventional symbol for admittance itself through the publications of Charles Proteus Steinmetz. Heaviside probably chose Y simply because it is next to Z in the alphabet, the conventional symbol for impedance.
In electrical engineering, susceptance is the imaginary part of admittance, where the real part is conductance. The reciprocal of admittance is impedance, where the imaginary part is reactance and the real part is resistance. In SI units, susceptance is measured in siemens (S).
Acoustic impedance and specific acoustic impedance are measures of the opposition that a system presents to the acoustic flow resulting from an acoustic pressure applied to the system. The SI unit of acoustic impedance is the pascal-second per cubic metre, or in the MKS system the rayl per square metre, while that of specific acoustic impedance is the pascal-second per metre, or in the MKS system the rayl. There is a close analogy with electrical impedance, which measures the opposition that a system presents to the electric current resulting from a voltage applied to the system.
In physics, the weber is the unit of magnetic flux in the International System of Units (SI). The unit is derived from the relationship 1 Wb = 1 V⋅s (volt-second). A magnetic flux density of 1 Wb/m2 is one tesla.
Permeance, in general, is the degree to which a material admits a flow of matter or energy. Permeance is usually represented by a curly capital P: P.
The ohm is the unit of electrical resistance in the International System of Units (SI). It is named after German physicist Georg Ohm. Various empirically derived standard units for electrical resistance were developed in connection with early telegraphy practice, and the British Association for the Advancement of Science proposed a unit derived from existing units of mass, length and time, and of a convenient scale for practical work as early as 1861.
In electromagnetism, the impedance of free space, Z0, is a physical constant relating the magnitudes of the electric and magnetic fields of electromagnetic radiation travelling through free space. That is,
A conventional electrical unit is a unit of measurement in the field of electricity which is based on the so-called "conventional values" of the Josephson constant, the von Klitzing constant agreed by the International Committee for Weights and Measures (CIPM) in 1988, as well as ΔνCs used to define the second. These units are very similar in scale to their corresponding SI units, but are not identical because of the different values used for the constants. They are distinguished from the corresponding SI units by setting the symbol in italic typeface and adding a subscript "90" – e.g., the conventional volt has the symbol V90 – as they came into international use on 1 January 1990.
The watt is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named in honor of James Watt (1736–1819), an 18th-century Scottish inventor, mechanical engineer, and chemist who improved the Newcomen engine with his own steam engine in 1776. Watt's invention was fundamental for the Industrial Revolution.
The first International Exposition of Electricity ran from 15 August 1881 through to 15 November 1881 at the Palais de l'Industrie on the Champs-Élysées in Paris, France. It served to display the advances in electrical technology since the small electrical display at the 1878 Universal Exposition. Exhibitors came from the United Kingdom, United States, Germany, Italy and the Netherlands, as well as from France. As part of the exhibition, the first International Congress of Electricians presented numerous scientific and technical papers, including definitions of the standard practical units volt, ohm and ampere.
Performance modelling is the abstraction of a real system into a simplified representation to enable the prediction of performance. The creation of a model can provide insight into how a proposed or actual system will or does work. This can, however, point towards different things to people belonging to different fields of work.
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