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admittance

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 & resistance are defined. The SI unit of admittance is the siemens (symbol S); the older, synonymous unit is mho, and its symbol is ℧ (an upside-down uppercase omega Ω). Oliver Heaviside coined the term admittance in December 1887.Admittance is defined as




Y
≡


1
Z





{\displaystyle Y\equiv {\frac {1}{Z}}\,}
where

Y is the admittance, measured in siemens
Z is the impedance, measured in ohmsResistance is a measure of the opposition of a circuit to the flow of a steady current, while impedance takes into account not only the resistance but also dynamic effects (known as reactance). Likewise, admittance is not only a measure of the ease with which a steady current can flow, but also the dynamic effects of the material's susceptance to polarization:




Y
=
G
+
j
B



{\displaystyle Y=G+jB\,}
where




Y


{\displaystyle Y}
is the admittance, measured in siemens.




G


{\displaystyle G}
is the conductance, measured in siemens.




B


{\displaystyle B}
is the susceptance, measured in siemens.





j

2


=
−
1


{\displaystyle j^{2}=-1}
The dynamic effects of the material's susceptance relate to the universal dielectric response, the power law scaling of a system's admittance with frequency under alternating current conditions.

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