Electromagnetic Units in Various CGS Systems
| Quantity | Symbol | SI unit | ESU unit | EMU unit | Gaussian unit |
|---|---|---|---|---|---|
| electric charge | q | 1 C | = (10−1 c) statC | = (10−1) abC | = (10−1 c) Fr |
| electric current | I | 1 A | = (10−1 c) statA | = (10−1) abA | = (10−1 c) Fr·s−1 |
| electric potential voltage |
φ V |
1 V | = (108 c−1) statV | = (108) abV | = (108 c−1) statV |
| electric field | E | 1 V/m | = (106 c−1) statV/cm | = (106) abV/cm | = (106 c−1) statV/cm |
| magnetic B field | B | 1 T | = (104 c−1) statT | = (104) G | = (104) G |
| magnetic H field | H | 1 A/m | = (4π 10−3 c) statA/cm | = (4π 10−3) Oe | = (4π 10−3) Oe |
| magnetic dipole moment | μ | 1 A·m² | = (103 c) statA·cm² | = (103) abA·cm² | = (103) erg/G |
| magnetic flux | Φm | 1 Wb | = (108 c−1) statT·cm² | = (108) Mx | = (108) G·cm² |
| resistance | R | 1 Ω | = (109 c−2) s/cm | = (109) abΩ | = (109 c−2) s/cm |
| resistivity | ρ | 1 Ω·m | = (1011 c−2) s | = (1011) abΩ·cm | = (1011 c−2) s |
| capacitance | C | 1 F | = (10−9 c2) cm | = (10−9) abF | = (10−9 c2) cm |
| inductance | L | 1 H | = (109 c−2) cm−1·s2 | = (109) abH | = (109 c−2) cm−1·s2 |
In this table, c = 29,979,245,800 ≈ 3·1010 is the speed of light in vacuum in the CGS units of cm/s.
One can think of the SI value of the Coulomb constant kC as:
This explains why SI to ESU conversions involving factors of c2 lead to significant simplifications of the ESU units, such as 1 statF = 1 cm and 1 statΩ = 1 s/cm: this is the consequence of the fact that in ESU system kC=1. For example, a centimetre of capacitance is the capacitance between a sphere of radius 1 cm in vacuum and infinity. The capacitance C between two concentric spheres of radii R and r in ESU CGS system is:
- .
By taking the limit as R goes to infinity we see C equals r.
Read more about this topic: Centimetre–gram–second System Of Units
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