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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