Electronics


Basics

Kirchhoff's Rules

Current Rule or Junction Rule (conservation of charge)
 
The algebraic sum of the currents entering any junction must equal the sum of the currents leaving that junction.
Therefore, in a series circuit the current is the same everywhere.
 
Voltage Rule or Loop Rule (conservation of energy)
 
The algebraic sum of the potential differences (voltage drops) around a closed conducting loop must equal zero.
Therefore, components connected in parallel have the same voltage across them.

Ohm's Law

V = IR

where voltage V is in volts, resistance R is in ohms and current I is in amperes.


Joule's Law

P = I^2R = V^2/R = VI

where power P is in Watts, voltage V is in volts, resistance R is in ohms and current I is in amperes.


Thévenin's Theorem

Any two-terminal network of resistors and voltage sources is equivalent to a single resistor in series with a single voltage source.


Definitions

1 ampere = 1 coulomb/second

1 coulomb = 1 ampere · second

1 farad = 1 coulomb/volt

1 joule = 1 newton · meter

1 newton = 1 kg · meter/second2

1 ohm = 1 volt/ampere

1 volt = 1 joule/coulomb

1 Watt = 1 joule/second


Symbols, Dimensions and Units of Physical Quantities

QuantityCommon
Symbol
UnitUnit
Symbol
CapacitanceCfaradF
Charge, electricalq, Q, ecoulombC
CurrentIampereA
EnergyE, UjouleJ
ForceFnewtonN
Frequencyf, vhertzHz
Lengthl, Lmeterm
Potential, electrical
or Voltage
VvoltV
PowerPWattW
ResistanceRohmOmega
Timetseconds
WorkWjouleJ


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DISCLAIMER

Page author: Dawn Rorvik (rorvikd@evergreen.edu)
Last modified: 05/20/2003