Electrical Units

Ratio of SI unit Magnitude of Quantity Symbol Equation SI unit symbol CGS unit SI to cgs unit Z Current , i I=/; I = E/Z; I = Q/t A 10-1 Quantity Q, q Q = it; Q = CE C 10-1 E, e E = IR; E = W/Q V 108 Resistance R, r R=E/I; R = ␳l /A 109 Resistivity ␳␳= RA / I Ohm- Ω•m Abohm-cm 1011 Conductance G, g G =␥ A / l G = A/␳l S 10-9 Conductivity ␥␥ = 1/␳; ␥ = I/ RA Siemens/meter S/m Abmho/cm 10-11 C C = Q/E F Abfarad* 10-9 /meter F/m Stat farad*/cm 8.85 X 10-12

Relative permittivity ⑀r ⑀r = ⑀ր⑀␱ Numerical Numerical I Self- L L = - N(d␾րdt) H 109 1/2 9 Mutual inductance M M = K(L1L2) Henry H Abhenry 10 J J = eit J 107 kwh kwh = kw/3600; 3.6 MJ Kilowatthour kWh 36 X 1012 Active W W = J/t; W = EI cos ⍜ W Abwatt 107 Reactive power jQ Q = sin ⍜ Var var Abvar 107 Apparent power VA VA = El Volt-ampere VA Power factor pf pf = W/VA; pf = W/(W + jQ) 1 ␲ Ω 9 Reactance, inductive XL XL = 2 fL Ohm Abohm 10 ␲ Ω 9 Reactance, capacitive XC XC = 1/(2 fC) Ohm Abohm 10 Ω 9 Impedance Z Z = E/I Z = R + j(XL - XC) Ohm Abohm 10 Conductance G G = R/Z2 Siemens S Abmho 10-9 B B = X/Z2 Siemens S Abmho 10-9 Y Y =I/E; Y = G + jB Siemens S Abmho 10-9 Frequency f f = 1/T Hz Cps Hz 1 Period T T = 1/f s Second 1 T L/R; RC Second s Second 1 Angular velocity ωω= 2πf /second /s Radians/second 1

*1 Abfarad (EMU Units) = 9 X 10-20 stat farads (ESU units).

Reproduced with Permission from McGraw-Hill, Marks’ Standard Handbook for Mechanical Engineers, 8th ed. Authors: Baumeister, et al. Copyright 1987

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