Physics Formulae/Electric Circuits Formulae

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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 | edit source]

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 | edit source]

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