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


    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


    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