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Contents

   



(Top)
 


1 Definitions  



1.1  Initial quantities  





1.2  Electric quantities  





1.3  Magnetic quantities  





1.4  Electric circuits  





1.5  Magnetic circuits  







2 Electromagnetism  



2.1  Electric fields  





2.2  Magnetic fields and moments  







3 Electric circuits and electronics  





4 See also  





5 Footnotes  





6 Sources  





7 Further reading  














List of electromagnetism equations







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From Wikipedia, the free encyclopedia
 


This article summarizes equations in the theory of electromagnetism.

Definitions

[edit]
Lorentz force on a charged particle (ofcharge q) in motion (velocity v), used as the definition of the E field and B field.

Here subscripts e and m are used to differ between electric and magnetic charges. The definitions for monopoles are of theoretical interest, although real magnetic dipoles can be described using pole strengths. There are two possible units for monopole strength, Wb (Weber) and A m (Ampere metre). Dimensional analysis shows that magnetic charges relate by qm(Wb) = μ0 qm(Am).

Initial quantities

[edit]
Quantity (common name/s) (Common) symbol/s SI units Dimension
Electric charge qe, q, Q C = As [I][T]
Monopole strength, magnetic charge qm, g, p Wb or Am [L]2[M][T]−2 [I]−1 (Wb)

[I][L] (Am)

Electric quantities

[edit]
Continuous charge distribution. The volume charge density ρ is the amount of charge per unit volume (cube), surface charge density σ is amount per unit surface area (circle) with outward unit normal , d is the dipole moment between two point charges, the volume density of these is the polarization density P. Position vector r is a point to calculate the electric field; r is a point in the charged object.

Contrary to the strong analogy between (classical) gravitation and electrostatics, there are no "centre of charge" or "centre of electrostatic attraction" analogues.

Electric transport

Quantity (common name/s) (Common) symbol/s Defining equation SI units Dimension
Linear, surface, volumetric charge density λe for Linear, σe for surface, ρe for volume.

C mn, n = 1, 2, 3 [I][T][L]n
Capacitance C

V = voltage, not volume.

F = C V−1 [I]2[T]4[L]−2[M]−1
Electric current I A [I]
Electric current density J A m−2 [I][L]−2
Displacement current density Jd A m−2 [I][L]−2
Convection current density Jc A m−2 [I][L]−2

Electric fields

Quantity (common name/s) (Common) symbol/s Defining equation SI units Dimension
Electric field, field strength, flux density, potential gradient E N C−1 = V m−1 [M][L][T]−3[I]−1
Electric flux ΦE N m2C−1 [M][L]3[T]−3[I]−1
Absolute permittivity; ε F m−1 [I]2 [T]4 [M]−1 [L]−3
Electric dipole moment p

a = charge separation directed from -ve to +ve charge

C m [I][T][L]
Electric Polarization, polarization density P C m−2 [I][T][L]−2
Electric displacement field, flux density D C m−2 [I][T][L]−2
Electric displacement flux ΦD C [I][T]
Absolute electric potential, EM scalar potential relative to point

Theoretical:
Practical: (Earth's radius)

φ ,V V = J C−1 [M] [L]2 [T]−3 [I]−1
Voltage, Electric potential difference ΔφV V = J C−1 [M] [L]2 [T]−3 [I]−1

Magnetic quantities

[edit]

Magnetic transport

Quantity (common name/s) (Common) symbol/s Defining equation SI units Dimension
Linear, surface, volumetric pole density λm for Linear, σm for surface, ρm for volume.

Wb mn

A m(−n + 1),
n = 1, 2, 3

[L]2[M][T]−2 [I]−1 (Wb)

[I][L] (Am)

Monopole current Im Wb s−1

A m s−1

[L]2[M][T]−3 [I]−1 (Wb)

[I][L][T]−1 (Am)

Monopole current density Jm Wb s−1m−2

A m−1s−1

[M][T]−3 [I]−1 (Wb)

[I][L]−1[T]−1 (Am)

Magnetic fields

Quantity (common name/s) (Common) symbol/s Defining equation SI units Dimension
Magnetic field, field strength, flux density, induction field B T = N A−1m−1 = Wb m−2 [M][T]−2[I]−1
Magnetic potential, EM vector potential A T m = N A−1 = Wb m3 [M][L][T]−2[I]−1
Magnetic flux ΦB Wb = T m2 [L]2[M][T]−2[I]−1
Magnetic permeability V·s·A−1·m−1 = N·A−2 = T·m·A−1 = Wb·A−1·m−1 [M][L][T]−2[I]−2
Magnetic moment, magnetic dipole moment m, μB, Π

Two definitions are possible:

using pole strengths,

using currents:

a = pole separation

N is the number of turns of conductor

A m2 [I][L]2
Magnetization M A m−1 [I] [L]−1
Magnetic field intensity, (AKA field strength) H Two definitions are possible:

most common:

using pole strengths,[1]

A m−1 [I] [L]−1
Intensity of magnetization, magnetic polarization I, J T = N A−1m−1 = Wb m−2 [M][T]−2[I]−1
Self Inductance L Two equivalent definitions are possible:

H = Wb A−1 [L]2 [M] [T]−2 [I]−2
Mutual inductance M Again two equivalent definitions are possible:

1,2 subscripts refer to two conductors/inductors mutually inducing voltage/ linking magnetic flux through each other. They can be interchanged for the required conductor/inductor;


H = Wb A−1 [L]2 [M] [T]−2 [I]−2
Gyromagnetic ratio (for charged particles in a magnetic field) γ Hz T−1 [M]−1[T][I]

Electric circuits

[edit]

DC circuits, general definitions

Quantity (common name/s) (Common) symbol/s Defining equation SI units Dimension
Terminal Voltage for

Power Supply

Vter V = J C−1 [M] [L]2 [T]−3 [I]−1
Load Voltage for Circuit Vload V = J C−1 [M] [L]2 [T]−3 [I]−1
Internal resistance of power supply Rint Ω = V A−1 = J s C−2 [M][L]2 [T]−3 [I]−2
Load resistance of circuit Rext 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 E V = J C−1 [M] [L]2 [T]−3 [I]−1

AC circuits

Quantity (common name/s) (Common) symbol/s Defining equation SI units Dimension
Resistive load voltage VR V = J C−1 [M] [L]2 [T]−3 [I]−1
Capacitive load voltage VC V = J C−1 [M] [L]2 [T]−3 [I]−1
Inductive load voltage VL V = J C−1 [M] [L]2 [T]−3 [I]−1
Capacitive reactance XC Ω−1m−1 [I]2 [T]3 [M]−2 [L]−2
Inductive reactance XL Ω−1m−1 [I]2 [T]3 [M]−2 [L]−2
AC electrical impedance Z

Ω−1m−1 [I]2 [T]3 [M]−2 [L]−2
Phase constant δ, φ dimensionless dimensionless
AC peak current I0 A [I]
AC root mean square current Irms A [I]
AC peak voltage V0 V = J C−1 [M] [L]2 [T]−3 [I]−1
AC root mean square voltage Vrms 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 τC s [T]
Inductive time constant τL s [T]

Magnetic circuits

[edit]
Quantity (common name/s) (Common) symbol/s Defining equation SI units Dimension
Magnetomotive force, mmf F,

N = number of turns of conductor

A [I]

Electromagnetism

[edit]

Electric fields

[edit]

General Classical Equations

Physical situation Equations
Electric potential gradient and field

Point charge
At a point in a local array of point charges
At a point due to a continuum of charge
Electrostatic torque and potential energy due to non-uniform fields and dipole moments

Magnetic fields and moments

[edit]

General classical equations

Physical situation Equations
Magnetic potential, EM vector potential
Due to a magnetic moment

Magnetic moment due to a current distribution
Magnetostatic torque and potential energy due to non-uniform fields and dipole moments

Electric circuits and electronics

[edit]

Below N = number of conductors or circuit components. Subscript net refers to the equivalent and resultant property value.

Physical situation Nomenclature Series Parallel
Resistors and conductors
  • Ri = resistance of resistor or conductor i
  • Gi = conductance of resistor or conductor i
  • Charge, capacitors, currents
    • Ci = capacitance of capacitor i
  • qi = charge of charge carrier i
  • Inductors
    • Li = self-inductance of inductor i
  • Lij = self-inductance element ijofL matrix
  • Mij = mutual inductance between inductors i and j
  • Circuit DC Circuit equations AC Circuit equations
    Series circuit equations
    RC circuits Circuit equation

    Capacitor charge

    Capacitor discharge

    RL circuits Circuit equation

    Inductor current rise

    Inductor current fall

    LC circuits Circuit equation

    Circuit equation

    Circuit resonant frequency

    Circuit charge

    Circuit current

    Circuit electrical potential energy

    Circuit magnetic potential energy

    RLC Circuits Circuit equation

    Circuit equation

    Circuit charge

    See also

    [edit]

    Footnotes

    [edit]
    1. ^ M. Mansfield; C. O'Sullivan (2011). Understanding Physics (2nd ed.). John Wiley & Sons. ISBN 978-0-470-74637-0.

    Sources

    [edit]

    Further reading

    [edit]
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    This page was last edited on 31 March 2024, at 14:57 (UTC).

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