Electromagnetism - Units

Units

Electromagnetic units are part of a system of electrical units based primarily upon the magnetic properties of electric currents, the fundamental SI unit being the ampere. The units are:

  • ampere (electric current)
  • coulomb (electric charge)
  • farad (capacitance)
  • henry (inductance)
  • ohm (resistance)
  • tesla (magnetic flux density)
  • volt (electric potential)
  • watt (power)
  • weber (magnetic flux)

In the electromagnetic cgs system, electric current is a fundamental quantity defined via Ampère's law and takes the permeability as a dimensionless quantity (relative permeability) whose value in a vacuum is unity. As a consequence, the square of the speed of light appears explicitly in some of the equations interrelating quantities in this system.

SI electromagnetism units
Symbol Name of Quantity Derived Units Unit Base Units
I Electric current ampere (SI base unit) A A (= W/V = C/s)
Q Electric charge coulomb C A·s
U, ΔV, Δφ; E Potential difference; Electromotive force volt V kg·m2·s−3·A−1 (= J/C)
R; Z; X Electric resistance; Impedance; Reactance ohm Ω kg·m2·s−3·A−2 (= V/A)
ρ Resistivity ohm metre Ω·m kg·m3·s−3·A−2
P Electric power watt W kg·m2·s−3 (= V·A)
C Capacitance farad F kg−1·m−2·s4·A2 (= C/V)
E Electric field strength volt per metre V/m kg·m·s−3·A−1 (= N/C)
D Electric displacement field Coulomb per square metre C/m2 A·s·m−2
ε Permittivity farad per metre F/m kg−1·m−3·s4·A2
χe Electric susceptibility (dimensionless) - -
G; Y; B Conductance; Admittance; Susceptance siemens S kg−1·m−2·s3·A2 (= Ω−1)
κ, γ, σ Conductivity siemens per metre S/m kg−1·m−3·s3·A2
B Magnetic flux density, Magnetic induction tesla T kg·s−2·A−1 (= Wb/m2 = N·A−1·m−1)
Φ Magnetic flux weber Wb kg·m2·s−2·A−1 (= V·s)
H Magnetic field strength ampere per metre A/m A·m−1
L, M Inductance henry H kg·m2·s−2·A−2 (= Wb/A = V·s/A)
μ Permeability henry per metre H/m kg·m·s−2·A−2
χ Magnetic susceptibility (dimensionless) - -

Read more about this topic:  Electromagnetism

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