Ampere to EMU of current
A
EMU
Conversion History
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Quick Reference Table (Ampere to EMU of current)
| Ampere (A) | EMU of current (EMU) |
|---|---|
| 0.5 | 0.05 |
| 1 | 0.1 |
| 5 | 0.5 |
| 10 | 1 |
| 13 | 1.3 |
| 20 | 2 |
| 32 | 3.2 |
| 100 | 10 |
About Ampere (A)
The ampere (A) is the SI base unit of electric current, one of the seven fundamental units in the International System. Since the 2019 SI redefinition, one ampere is exactly the flow of 1/1.602176634×10⁻¹⁹ elementary charges per second, fixing the elementary charge precisely. In practice, a 100 W bulb at 240 V draws about 0.4 A; a domestic kettle draws 8–13 A; household ring circuits are protected at 20–32 A; car starter motors demand brief surges of 100–200 A. The ampere defines related units: one volt across one ohm yields one ampere (Ohm s law), and one ampere for one second transfers one coulomb of charge.
A smartphone fast charger delivers 2–5 A. A household circuit breaker protects wiring rated at 10–32 A.
Etymology: Named after André-Marie Ampère (1775–1836), French physicist and mathematician who formulated Ampère s circuital law relating magnetic fields to the electric currents that produce them. The ampere was adopted as a practical electrical unit at the International Electrical Congress in 1881.
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.
Ampere – Frequently Asked Questions
Why was the ampere redefined in 2019?
The old definition relied on a thought experiment — infinite parallel wires 1 meter apart — that was impossible to realize exactly in a lab. The 2019 redefinition fixed the elementary charge at exactly 1.602176634×10⁻¹⁹ coulombs, linking the ampere to a countable number of electrons per second and enabling more precise quantum-based measurements.
How many amps does a house use at peak?
A typical US home has a 200-amp service panel. Peak usage — oven, dryer, AC, and water heater all running — might hit 80–150 A across all circuits combined. The 200 A main breaker protects the service entrance cable. European homes typically have 32–63 A single-phase service at 230 V, delivering equivalent power.
Why do electricians say "it is the amps that kill you, not the volts"?
Current through the heart causes fibrillation and death — as little as 0.1 A at 50/60 Hz. But voltage drives that current through your body's resistance (~1,000–100,000 ohms depending on conditions). So you need enough voltage to push lethal current through skin resistance. Both matter; the saying is a simplification.
What happens inside a circuit breaker the instant current exceeds its rating?
A thermal-magnetic breaker has two trip mechanisms. For sustained overloads (e.g., 20 A on a 15 A breaker), a bimetallic strip slowly heats and bends until it releases the latch — taking seconds to minutes depending on the overload. For short circuits (hundreds of amps), an electromagnet yanks the latch open in milliseconds. The contacts separate and an arc forms; arc chutes — stacked steel plates — split the arc into segments, cool it, and extinguish it within one AC cycle (16–20 ms). Modern breakers can interrupt 10,000–65,000 A fault currents.
How does a clamp meter measure amps without touching the wire?
A clamp meter wraps a magnetic core around a current-carrying conductor. AC current creates an alternating magnetic field that induces a proportional voltage in the clamp's pickup coil. Hall-effect clamp meters can also measure DC. No electrical contact needed — you just close the jaws around the insulated wire.
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.