Appendix A: SI Units and Quantities
Pages 2

Admittance Y (ohm) Charge (quantity) Q C (coulomb) Conductance G S (siemen) Current I A (ampere) Current density J A/m 2 (ampere/square metre) Electromotive force (emf) E V (volts) Frequency f Hz (hertz) Impedance Z (ohm) Period T s (second) Potential difference (p.d.) V V (volt) Power, active P W (watt) Power, apparent S VA (volt ampere) Power, reactive Q VAr (volt ampere reactive) Reactance X (ohm) Resistance R (ohm) Resistivity m (ohm metre) Time constant s (second)

Electrostatic quantities Symbol Unit

Capacitance C F (farad) Field strength E V/m (volt/metre) Flux C (coulomb) Flux density D C/m 2 (coulomb/square metre) Permittivity, absolute e F/m (farad/metre)

General quantities Symbol Unit

Permittivity, relative er no units Permittivity, of free space e0 F/m (farad/metre)

Electromagnetic quantities Symbol Unit

Field strength H A/m (ampere/metre) (1) Flux Wb (weber) Flux density B T (tesla) Inductance, mutual M H (henry) Inductance, self L H (henry) Magnetomotive force (mmf) F A (ampere) (2) Permeability, absolute H/m (henry/metre) Permeability, relative r no units Permeability, of free space 0 H/m (henry/metre) Reluctance S A/Wb (ampere/weber) (3)

(1) At/m (ampere turn/metre) in this book (2) (ampere turn) in this book (3) At/Wb (ampere turn/weber) in this book