Electrical Units
Quantity
Current
Quantity
Electromotive force
Resistance
Resistivity
Conductance
Conductivity
Capacitance
Permittivity
Relative permittivity
Self-inductance
Mutual inductance
Energy
Active power
Reactive power
Apparent power
Power factor
Reactance, inductive
Reactance, capacitive
Impedance
Conductance
Susceptance
Admittance
Frequency
Period
Time constant
Angular velocity
Symbol
I, i
Q, q
E, e
R, r
r
G, g
g
C
e
er
L
M
J
kwh
W
jQ
VA
pf
XL
XC
Z
G
B
Y
f
T
T
ω
Equation
I=E/R; I = E/Z; I = Q/t
Q = it; Q = CE
E = IR; E = W/Q
R=E/I; R = rl /A
r = RA / I
G =g A / l G = A/rl
g = 1/r; g = I/ RA
C = Q/E
er = e/eo
L = - N(df/dt)
M = K(L1L2) 1/2
J = eit
kwh = kw/3600; 3.6 MJ
W = J/t; W = EI cos U
Q = El sin U
VA = El
pf = W/VA; pf = W/(W + jQ)
XL = 2pfL
XC = 1/(2pfC)
Z = E/I Z = R + j(XL - XC)
G = R/Z2
B = X/Z2
Y =I/E; Y = G + jB
f = 1/T
T = 1/f
L/R; RC
ω = 2πf
SI unit
SI unit
symbol
Ampere
A
Coulomb
C
Volt
V
Ohm
Ω
Ohm-metre
Ω•m
Siemens
S
Siemens/meter
S/m
Farad
F
Farads/meter
F/m
Numerical
Henry
H
Henry
H
Joule
J
Kilowatthour
kWh
Watt
W
Var
var
Volt-ampere
VA
Ohm
Ohm
Ohm
Siemens
Siemens
Siemens
Hertz
Second
Second
Radians/second
Ω
Ω
Ω
S
S
S
Hz
s
s
rad/s
Ratio of
Magnitude of
CGS unit
SI to cgs unit
Abampere
10-1
Abcoulomb
10-1
Abvolt
108
Abohm
109
Abohm-cm
1011
Abmho
10-9
Abmho/cm
10-11
Abfarad*
10-9
Stat farad*/cm 8.85 X 10-12
Numerical
I
Abhenry
109
Abhenry
109
Erg
107
36 X 1012
Abwatt
107
Abvar
107
Abohm
Abohm
Abohm
Abmho
Abmho
Abmho
Cps Hz
Second
Second
Radians/second
1
109
109
109
10-9
10-9
10-9
1
1
1
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
Z-264
Z
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