List of electromagnetism equations
This article summarizes equations in the theory of electromagnetism.
Definitions
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
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
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 m−n, 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 m2 C−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 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 Δφ,ΔV V = J C−1 [M] [L]2 [T]−3 [I]−1
Magnetic quantities
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 m−n
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−1 m−2
A m−1 s−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−1 m−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−1 m−1 = Wb m2 [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
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−1 m−1 [I]2 [T]3 [M]−2 [L]−2 Inductive reactance XL Ω−1 m−1 [I]2 [T]3 [M]−2 [L]−2 AC electrical impedance Z Ω−1 m−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
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
Electric fields
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
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
Electromagnetic induction
Physical situation Nomenclature Equations Transformation of voltage - N = number of turns of conductor
- η = energy efficiency
Electric circuits and electronics
Below N = number of conductors or circuit components. Subcript 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 ij of L 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
- Defining equation (physical chemistry)
- List of equations in classical mechanics
- List of equations in fluid mechanics
- List of equations in gravitation
- List of equations in nuclear and particle physics
- List of equations in quantum mechanics
- List of equations in wave theory
- List of photonics equations
- List of relativistic equations
- SI electromagnetism units
- Table of thermodynamic equations
Footnotes
- M. Mansfield; C. O'Sullivan (2011). Understanding Physics (2nd ed.). John Wiley & Sons. ISBN 978-0-470-74637-0.
Sources
- P.M. Whelan; M.J. Hodgeson (1978). Essential Principles of Physics (2nd ed.). John Murray. ISBN 0-7195-3382-1.
- G. Woan (2010). The Cambridge Handbook of Physics Formulas. Cambridge University Press. ISBN 978-0-521-57507-2.
- A. Halpern (1988). 3000 Solved Problems in Physics, Schaum Series. Mc Graw Hill. ISBN 978-0-07-025734-4.
- R.G. Lerner; G.L. Trigg (2005). Encyclopaedia of Physics (2nd ed.). VHC Publishers, Hans Warlimont, Springer. pp. 12–13. ISBN 978-0-07-025734-4.
- C.B. Parker (1994). McGraw Hill Encyclopaedia of Physics (2nd ed.). McGraw Hill. ISBN 0-07-051400-3.
- P.A. Tipler; G. Mosca (2008). Physics for Scientists and Engineers: With Modern Physics (6th ed.). W.H. Freeman and Co. ISBN 978-1-4292-0265-7.
- L.N. Hand; J.D. Finch (2008). Analytical Mechanics. Cambridge University Press. ISBN 978-0-521-57572-0.
- T.B. Arkill; C.J. Millar (1974). Mechanics, Vibrations and Waves. John Murray. ISBN 0-7195-2882-8.
- H.J. Pain (1983). The Physics of Vibrations and Waves (3rd ed.). John Wiley & Sons. ISBN 0-471-90182-2.
- J.R. Forshaw; A.G. Smith (2009). Dynamics and Relativity. Wiley. ISBN 978-0-470-01460-8.
- G.A.G. Bennet (1974). Electricity and Modern Physics (2nd ed.). Edward Arnold (UK). ISBN 0-7131-2459-8.
- I.S. Grant; W.R. Phillips; Manchester Physics (2008). Electromagnetism (2nd ed.). John Wiley & Sons. ISBN 978-0-471-92712-9.
- D.J. Griffiths (2007). Introduction to Electrodynamics (3rd ed.). Pearson Education, Dorling Kindersley. ISBN 81-7758-293-3.
Further reading
- L.H. Greenberg (1978). Physics with Modern Applications. Holt-Saunders International W.B. Saunders and Co. ISBN 0-7216-4247-0.
- J.B. Marion; W.F. Hornyak (1984). Principles of Physics. Holt-Saunders International Saunders College. ISBN 4-8337-0195-2.
- A. Beiser (1987). Concepts of Modern Physics (4th ed.). McGraw-Hill (International). ISBN 0-07-100144-1.
- H.D. Young; R.A. Freedman (2008). University Physics – With Modern Physics (12th ed.). Addison-Wesley (Pearson International). ISBN 0-321-50130-6.