EMU of current to Gaussian electric current
EMU
G cgs
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
1 EMU (EMU of current) → 29979245817.809 G cgs (Gaussian electric current) Just now |
Quick Reference Table (EMU of current to Gaussian electric current)
| EMU of current (EMU) | Gaussian electric current (G cgs) |
|---|---|
| 0.1 | 2,997,924,581.7809 |
| 0.5 | 14,989,622,908.9045 |
| 1 | 29,979,245,817.809 |
| 5 | 149,896,229,089.045 |
| 10 | 299,792,458,178.09 |
| 30 | 899,377,374,534.27 |
| 100 | 2,997,924,581,780.9 |
About EMU of current (EMU)
The electromagnetic unit (EMU) of current equals exactly 10 amperes, numerically identical to the biot. It is the current unit native to the CGS electromagnetic (CGS-EMU) system, which dominated electrical physics from the mid-19th century until SI adoption in 1960. In CGS-EMU, the permeability of free space is defined as 1, giving the electromagnetic subsystem its characteristic form where magnetic force between parallel currents is expressed purely in dynes. The EMU of current appears in classical electrodynamics texts, historical measurement standards, and theoretical physics work using CGS-EMU conventions. All practical electrical measurement now uses SI amperes.
1 EMU of current = 10 A. A 50 A arc welding process carries 5 EMU. The unit is encountered primarily in pre-1960 scientific literature.
About Gaussian electric current (G cgs)
The Gaussian unit of electric current equals approximately 3.335641×10⁻¹⁰ amperes, derived from the Gaussian CGS system in which the speed of light c enters electromagnetic relations explicitly rather than through permittivity or permeability constants. One Gaussian current unit equals one statampere — one statcoulomb per second — and the SI conversion is I_SI = I_Gaussian × c_cm/s / 10, where c ≈ 2.998×10¹⁰ cm/s. The Gaussian system remains common in theoretical and computational physics, plasma physics, quantum electrodynamics, and astrophysics literature where its symmetric treatment of electric and magnetic fields simplifies equations.
1 Gaussian current unit ≈ 3.336×10⁻¹⁰ A. Plasma physics and astrophysics papers routinely quote electromagnetic quantities in Gaussian units rather than SI.
EMU of current – Frequently Asked Questions
What does EMU stand for and why was it created?
EMU stands for "electromagnetic unit." In the 1860s–1870s, physicists needed separate unit systems for electrostatic and electromagnetic phenomena because they had not yet unified them. The EMU system was built around magnetic force between currents, while the ESU system was built around Coulomb's electrostatic force. The ratio between them turned out to be the speed of light — a clue that led to Maxwell's equations.
Is the EMU of current the same as a biot?
Yes, exactly. Both equal 10 amperes. The biot is the named unit; "EMU of current" is the generic label. It is like saying "SI unit of force" versus "newton" — same thing, different label. The CGS-EMU system also has named units for other quantities: the gauss (magnetic field), the oersted (magnetising field), and the maxwell (magnetic flux).
Why did physics abandon the EMU system?
The EMU system was awkward for practical electrical engineering — 1 EMU of resistance (the abohm) equals 10⁻⁹ ohms, making everyday values absurdly large numbers. The SI system, adopted in 1960, unified mechanical and electrical units into one coherent framework with human-scale values. Practicality won over tradition.
Where might I encounter EMU of current in old scientific papers?
Pre-1960 physics journals, particularly in geomagnetism, plasma physics, and early electrical standards work, routinely use EMU. Geophysicists measuring Earth's magnetic field historically reported results in CGS-EMU units (gauss, oersted, EMU). Some geophysics reference data still has not been converted to SI.
How did the speed of light connect the EMU and ESU systems?
Weber and Kohlrausch discovered in 1856 that the ratio of the ESU to EMU charge was approximately 3×10¹⁰ cm/s — the speed of light. This was no coincidence: Maxwell showed that light is an electromagnetic wave, and the unit ratio reflects the fundamental coupling between electric and magnetic fields. One of the greatest insights in physics history, hidden in a unit conversion.
Gaussian electric current – Frequently Asked Questions
Why do astrophysicists prefer Gaussian units over SI?
In Gaussian units, electric and magnetic fields have the same dimensions, and Maxwell's equations look more symmetric — no ε₀ or μ₀ cluttering the formulas. When you study electromagnetic radiation in vacuum (starlight, cosmic rays, pulsar emissions), this symmetry is physically meaningful and simplifies calculations considerably.
What makes Gaussian CGS different from pure ESU or EMU?
Gaussian is a hybrid: it uses ESU conventions for electric quantities (charge, electric field, current) and EMU conventions for magnetic quantities (magnetic field, flux). This cherry-picking gives clean equations for both electrostatic and magnetic phenomena, at the cost of the speed of light appearing explicitly in equations linking electric and magnetic fields.
What happens to the fine-structure constant when you switch from SI to Gaussian units?
In SI, the fine-structure constant α = e²/(4πε₀ℏc) ≈ 1/137. In Gaussian units, ε₀ disappears and α simplifies to e²/(ℏc) — cleaner and more physically transparent. This is one reason particle physicists and quantum electrodynamics theorists favor Gaussian: fundamental constants combine more naturally, and the coupling strength of electromagnetism is immediately visible as α ≈ 1/137.
How do Gaussian units make Maxwell's equations look more elegant?
In Gaussian CGS, Maxwell's equations replace ε₀ and μ₀ with explicit factors of c, and the electric field E and magnetic field B end up with the same dimensions. The symmetric form ∇×E = −(1/c)∂B/∂t and ∇×B = (1/c)∂E/∂t reveals that E and B are equal partners in electromagnetic waves — a physical insight that SI's asymmetric constants obscure.
Why does Jackson's Classical Electrodynamics textbook use Gaussian units?
J.D. Jackson chose Gaussian units because they reveal the deep symmetry between electric and magnetic fields and make relativistic electrodynamics equations cleaner. His textbook, used in virtually every physics PhD program since 1962, cemented Gaussian as the "language" of theoretical electromagnetism. Later editions added SI appendices as a concession to modernity.