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BASIC ELECTRICAL ENGINEERING FORMULAS

BASIC ELECTRICAL CIRCUIT FORMULASIMPEDANCE VOLT-AMP EQUATIONS

CIRCUIT

ELEMENT absolutevalue complexform instantaneousvalues RMS values forsinusoidal signalsENERGY

(dissipated on Ror stored in L, C)

RESISTANCE R R v=iR Vrms=IrmsR E=Irms2RtINDUCTANCE 2fL jL v=Ldi/dt Vrms=Irms2fL E=Li2/2CAPACITANCE 1/(2fC) 1/jC i=Cdv/dt Vrms=Irms/(2fC) E=Cv2/2

Notes:R- electrical resistance in ohms, L- inductance in henrys, C- capacitance in farads, f - frequencyin hertz, t- time in seconds, 3.14159;=2f - angular frequency;

j - imaginary unit ( j2=-1 )

BASIC ELECTRICAL THEOREMS AND CIRCUIT ANALYSIS LAWS

LAW DEFINITION RELATIONSHIPOhm's Law modifiedfor AC circuits with

sinusoidal signals

=Z, where and - voltage andcurrent phasors, Z - compleximpedance(for resistive circuits: u=Ri )

Lorentz force law,Faraday's law and Drude

modelKirchhoff's CurrentLaw (KCL)

The sum of electric currents whichflow into any junction in an electriccircuit is equal to the sum of currentswhich flow out

Conservation of electriccharge

Kirchhoff's VoltageLaw (KVL) The sum of the electrical voltagesaround a closed circuit must be zero Conservation of energy

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EQUATIONS FOR SERIES AND PARALLEL CONNECTIONS

CIRCUITELEMENT

SERIESCONNECTION

PARALLELCONNECTION

RESISTANCERseries=

R1+R2+...

Rparallel=1/

(1/R1+1/R2+...)

INDUCTANCELseries=L1+L2+...

Lparallel=1/(1/L1+1/L2+...)

CAPACITANCECseries=

1/(1/C1+1/C2+...)

Cparallel=C1+C2+...

RLC IMPEDANCE FORMULAS

CIRCUIT CONNECTION COMPLEX FORM ABSOLUTE VALUE

Series

Z=R+jL+1/jC

Parallel

Z=1/(1/R+1/jL+jC)

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MAGNETIC FIELD UNITS AND EQUATIONS

QUANTITYSYM-BOL SI UNIT SI EQUATION

CGSUNIT

CGSEQUATION

CONVER-

SIONFACTORMagneticinduction B tesla (T) B=o(H+M) Gauss(G) B = H+4M 1 T =104GMagnetic

field strength Hampere/meter(A/m)

H = NI/lc( lc - magnetic

path, m)Oersted

(Oe)H = 0.4NI/lc(lc - magnetic

path, cm)1 A/m =4 10-3

OeMagnetic flux weber

(Wb)= BAc

(Ac - area,m2)

Maxwell(M) = BAc(Ac - area, cm2) 1 Wb =108M

Magnetization M ampere/meter(A/m)

M=m/V(m- totalmagneticmoment,

V- volume,m3 )

emu/cm3

M=m/V(m- totalmagneticmoment,

V- volume,cm3 )

1 A/m =10-3

emu / cm3

Magneticpermeability

of vacuum onewton/ampere2 o= 410-7 1 - 410-7

Inductance L henryL=oN

2

Ac/lc(N- turns,Ac- area, m2,lc - magnetic

path, m)henry

L=

=0.4N2

Ac/lc10-8

(N- turns,Ac-area, cm2,lc - magneticpath, cm)

1

Emf (voltage) V volt V= -Nd/dt(N- turns) volt

V= -10-8Nd/dt(N- turns) 1

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MAXWELL'S EQUATIONS IN FREE SPACE (IN SI UNITS)

LAW DIFFERENTIAL FORM INTEGRAL FORM

Gauss' law forelectricity

Gauss' law formagnetism

Faraday's lawof induction

Ampere's law

NOTES: E - electric field, - charge density, 0 8.8510-12- electric permittivity of free space, 3.14159,

k - Boltzmann's constant, q - charge, B - magnetic induction, - magnetic flux, J - current density, i - electriccurrent,c 299 792 458 m/s - the speed of light, 0= 410

-7- magnetic permeability of free space,- del operator (if

Vis a vector function, then. V- divergence ofV,V - the curl of V).

2009 Lazar RozenblatSMPS Power Supply Guide http://www.smps.us/- tutorials, electronics reference,formulas, schematics.

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