B is the symbol used to represent susceptance, a measure of how easily alternating current (AC) flows in a circuit due to capacitance or inductance.
In electrical engineering, B is the unit symbol for susceptance, which is the imaginary part of admittance—the reciprocal of impedance. While impedance reflects resistance to AC, susceptance shows how much AC is allowed to pass due to capacitors and inductors. Measured in siemens (S), susceptance differs from conductance by applying only to reactive elements. Positive values indicate capacitive effects, while negative values indicate inductive effects. Understanding susceptance is critical in telecommunications, AV systems, and building automation, where reactive currents influence signal phase, distortion, and impedance matching.
IEEE (Institute of Electrical and Electronics Engineers) and TIA (Telecommunications Industry Association).
The use of B as a symbol for susceptance emerged in mid-20th-century electrical engineering as part of standardizing complex admittance and impedance analysis. It remains a core notation in circuit theory and telecommunications engineering.