Microampere to EMU of current
μA
EMU
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
1 μA (Microampere) → 1e-7 EMU (EMU of current) Just now |
Quick Reference Table (Microampere to EMU of current)
| Microampere (μA) | EMU of current (EMU) |
|---|---|
| 1 | 0.0000001 |
| 10 | 0.000001 |
| 50 | 0.000005 |
| 100 | 0.00001 |
| 500 | 0.00005 |
| 1,000 | 0.0001 |
About Microampere (μA)
The microampere (μA) equals one millionth of an ampere (10⁻⁶ A) and is the standard unit for quiescent and standby currents in battery-powered electronics. Operational amplifier input bias currents, photodiode outputs under dim light, and EEG scalp electrode signals all fall in the microampere range. Many modern microcontrollers in low-power run mode consume under 100 μA, enabling coin-cell operation for months. Analytical instruments such as pH meters and reference electrodes operate at microampere levels to avoid disturbing the solution being measured. Implantable cardiac pacemakers deliver stimulation pulses of several hundred microamperes.
A cardiac pacemaker delivers stimulation pulses of roughly 100–500 μA. A modern ARM microcontroller in active low-power mode draws around 50–200 μA.
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.
Microampere – Frequently Asked Questions
How long can a coin cell battery last at microampere currents?
A CR2032 coin cell has about 225 mAh capacity. At 10 μA continuous draw, it lasts roughly 225,000 / 10 = 22,500 hours — about 2.5 years. At 1 μA, theoretical life exceeds 25 years, though self-discharge limits practical life to about 10 years.
Can microampere currents be dangerous to humans?
Not from shock — the perception threshold is about 500 μA (0.5 mA) for DC and 1,000 μA for AC at 60 Hz. However, microampere currents applied directly to the heart (e.g., through a catheter) can cause ventricular fibrillation at as little as 50–100 μA, which is why medical device safety standards are so strict.
Why do pH meters need to operate at microampere levels?
A glass pH electrode has an internal resistance of 10–1,000 megaohms. Drawing more than a few microamperes would cause voltage drops across this resistance, shifting the reading. Modern pH meters use high-input-impedance amplifiers that draw under 1 μA to avoid disturbing the electrochemical potential being measured.
What is quiescent current and why is it measured in microamperes?
Quiescent current (Iq) is what an IC draws when powered on but doing nothing — no signal processing, no load driving. For battery-powered designs, low Iq is critical. A voltage regulator with 1 μA Iq wastes far less standby power than one with 100 μA, directly extending battery life in always-on devices.
How does a pacemaker deliver just a few hundred microamperes so precisely?
Pacemakers use constant-current output stages that regulate pulse amplitude to within ±5 μA. The pulse is typically 100–500 μA for 0.4–1.5 ms, just enough to depolarise heart tissue and trigger a contraction. Modern devices automatically adjust the current to the minimum needed, conserving the battery for its 8–12 year design life.
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.