Physics Formulae/Electric Circuits Formulae

Lead Article: Tables of Physics Formulae


This article is a summary of the laws, principles, defining quantities, and useful formulae in the analysis of Electric Circuits, Electronics.

DC Quantities edit

Quantity (Common Name/s) (Common) Symbol/s Defining Equation SI Units Dimension
Electrical Resistance     Ω = V A-1 = J s C-2 [M][L]2 [T]-3 [I]-2
Resistivity, Scalar     Ω m [M]2 [L]2 [T]-3 [I]-2
Resistivity Temperature Coefficient,

Linear Temperature Dependance

    K-1 [Θ]-1
Terminal Voltage for

Power Supply

  V = J C-1 [M] [L]2 [T]-3 [I]-1
Load Voltage for Circuit   V = J C-1 [M] [L]2 [T]-3 [I]-1
Internal Resistance of

Power Supply

    Ω = V A-1 = J s C-2 [M][L]2 [T]-3 [I]-2
Load Resistance of

Circuit

    Ω = V A-1 = J s C-2 [M][L]2 [T]-3 [I]-2
Electromotive Force (emf), Voltage across

entire circuit including power supply, external

components and conductors

    V = J C-1 [M] [L]2 [T]-3 [I]-1
Electrical Conductance     S = Ω-1 [T]3 [I]2 [M]-1 [L]-2
Electrical Conductivity, Scalar     Ω-1 m-1 [I]2 [T]3 [M]-2 [L]-2
Electrical Conductivity, Tensor     Ω-1 m-1 [I]2 [T]3 [M]-2 [L]-2
Electrical Power     W = J s-1 [M] [L]2 [T]-3
emf Power     W = J s-1 [M] [L]2 [T]-3
Resistor Power Dissipation     W = J s-1 [M] [L]2 [T]-3
Resistors in Series  
Resistors in Parallel  
Ohm's Law Scalar form

 

Vector Form

 

Tensor Form, general applies to all points in a conductor

 

Kirchoff's Laws emf loop rule around any closed circuit

 

Current law at junctions

 

AC Quantitites edit

Quantity (Common Name/s) Common Name/s Quantity (Common Name/s) Quantity (Common Name/s) Quantity (Common Name/s)
Resistive Load Voltage     V = J C-1 [M] [L]2 [T]-3 [I]-1
Capacitive Load Voltage     V = J C-1 [M] [L]2 [T]-3 [I]-1
Inductive Load Voltage     V = J C-1 [M] [L]2 [T]-3 [I]-1
Capacitive Reactance     Ω-1 m-1 [I]2 [T]3 [M]-2 [L]-2
Inductive Reactance     Ω-1 m-1 [I]2 [T]3 [M]-2 [L]-2
AC Impedance    

 

Ω-1 m-1 [I]2 [T]3 [M]-2 [L]-2
Phase Constant     dimensionless dimensionless
AC Circuit Resonant

Pulsatance

    s-1 [T]-1
AC Peak Current     A [I]
AC Root Mean

Square Current

    A [I]
AC Peak Voltage     V = J C-1 [M] [L]2 [T]-3 [I]-1
AC Root Mean

Square Voltage

    V = J C-1 [M] [L]2 [T]-3 [I]-1
AC emf, Root Mean Square     V = J C-1 [M] [L]2 [T]-3 [I]-1
AC Average Power     W = J s-1 [M] [L]2 [T]-3
Capacitive Time Constant     s [T]
Inductive Time Constant     s [T]
RC Circuits RC Circuit Equation

 

RC Circuit Capacitor Charging

 

RL Circuits RL Circuit Equation

 

RL Circuit Current Rise

 

RL Circuit, Current Fall

 

LC Circuit LC Circuit Equation

 

LC Circuit Resonance

 

LC Circuit Charge

 

LC Circuit Current

 

LC Circuit electrical potential energy

 

LC circuit magnetic potential energy

 

RLC Circuits RLC Circuit Equation

 

RLC Circuit Charge