EMU of current to Kiloampere
EMU
kA
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
1 EMU (EMU of current) → 0.01 kA (Kiloampere) Just now |
Quick Reference Table (EMU of current to Kiloampere)
| EMU of current (EMU) | Kiloampere (kA) |
|---|---|
| 0.1 | 0.001 |
| 0.5 | 0.005 |
| 1 | 0.01 |
| 5 | 0.05 |
| 10 | 0.1 |
| 30 | 0.3 |
| 100 | 1 |
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 Kiloampere (kA)
The kiloampere (kA) equals one thousand amperes and appears where extremely high currents are generated or measured. A typical lightning bolt carries a peak current of 20–30 kA, though extreme strokes can exceed 200 kA. Industrial arc furnaces melting steel draw 50–100 kA through graphite electrodes. Aluminum electrolysis cells in smelters operate at 150–500 kA of continuous DC current per pot. Rail electromagnetic launchers pulse at hundreds of kiloamperes. Resistance spot welding uses 5–30 kA pulses lasting milliseconds to join metal sheets.
A typical lightning bolt peaks at 20–30 kA. Aluminum smelting cells run continuously at 150–300 kA of electrolysis current.
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.
Kiloampere – Frequently Asked Questions
How does a spot welder push 10,000 amps through two sheets of metal?
A spot welder uses a large step-down transformer: high voltage at low current on the primary becomes very low voltage (1–2 V) at enormous current (5–30 kA) on the secondary. The copper electrode tips concentrate this current into a small spot, melting the metal in milliseconds. Total power is only 10–60 kW — it is the concentration that does the work.
What happens to a wire if you put a kiloampere through it?
A typical 14 AWG house wire rated for 15 A would vaporise almost instantly at 1 kA — the I²R heating would melt copper in milliseconds. Industrial busbars carrying kiloamperes are massive rectangular copper or aluminum bars, sometimes water-cooled, with cross-sections of 10–100 cm² to keep current density manageable.
How much current does a lightning bolt actually carry?
A typical negative cloud-to-ground stroke peaks at 20–30 kA for about 1–2 microseconds. Positive lightning (rarer, about 5% of strikes) can exceed 300 kA. The total charge transferred is only 1–5 coulombs because the pulse is so brief — enormous current, tiny duration.
Why do aluminum smelters need hundreds of kiloamperes?
Aluminum oxide dissolved in molten cryolite at 960 degrees C requires direct electrolytic reduction to separate aluminum metal. Each smelting pot runs at 4–5 V but needs 150–500 kA because the electrochemical reaction requires massive charge transfer. A single smelter may consume 1–2 GW — as much as a small city.
What protects electrical systems from kiloampere fault currents?
Circuit breakers rated for 10–200 kA interrupting capacity use arc-quenching chambers to extinguish the plasma arc that forms when contacts open under fault current. High-rupture-capacity (HRC) fuses have sand-filled ceramic bodies that absorb the arc energy. Without these devices, a short circuit on a utility feed would weld everything in the panel into slag.