Biot to ESU of current
Bi
ESU
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
1 Bi (Biot) → 29979245368.43143491760654099167 ESU (ESU of current) Just now |
Quick Reference Table (Biot to ESU of current)
| Biot (Bi) | ESU of current (ESU) |
|---|---|
| 0.1 | 2,997,924,536.84314349176065409917 |
| 0.5 | 14,989,622,684.21571745880327049584 |
| 1 | 29,979,245,368.43143491760654099167 |
| 5 | 149,896,226,842.15717458803270495836 |
| 10 | 299,792,453,684.31434917606540991671 |
| 30 | 899,377,361,052.94304752819622975014 |
| 100 | 2,997,924,536,843.14349176065409916715 |
About Biot (Bi)
The biot (Bi) equals exactly 10 amperes and is the base unit of electric current in the centimeter-gram-second electromagnetic (CGS-EMU) system. It is defined as the current in a pair of parallel conductors 1 cm apart that produces a force of 2 dynes per centimeter length — the CGS-EMU analogue of the SI ampere definition. In the CGS-EMU system the biot plays the same foundational role the ampere plays in SI: all other electromagnetic CGS-EMU units are derived from it. The biot is essentially obsolete in modern practice, but it appears in older physics literature and classical electrodynamics textbooks alongside the dyne, gauss, and oersted.
A current of 1 Bi equals 10 A — roughly the draw of a domestic electric kettle. References to the biot appear primarily in historical or theoretical contexts, not modern instrumentation.
Etymology: Named after Jean-Baptiste Biot (1774–1862), French physicist who, with Félix Savart, established the Biot–Savart law describing the magnetic field generated by a steady electric current.
About ESU of current (ESU)
The electrostatic unit of current (ESU, also called the statampere) equals approximately 3.335641×10⁻¹⁰ amperes. It is the current unit of the CGS electrostatic system (CGS-ESU), in which Coulomb s law is written without a permittivity constant and electromagnetic quantities are derived from the statcoulomb (franklin). One statampere is the flow of one statcoulomb per second. The factor 3.336×10⁻¹⁰ arises because 1 A = (c/10) ESU, where c ≈ 3×10¹⁰ cm/s is the speed of light in CGS units. The CGS-ESU system was used in early electrostatics and vacuum tube physics but is entirely obsolete in applied engineering.
1 ESU of current ≈ 3.336×10⁻¹⁰ A — an extraordinarily small current. One ordinary ampere equals approximately 3×10⁹ ESU.
Biot – Frequently Asked Questions
Why is the biot exactly 10 amperes and not some other factor?
The CGS-EMU system defines its base units using centimeters, grams, and seconds instead of meters, kilograms, and seconds. The factor of 10 falls out naturally from the dimensional conversion: 1 Bi produces 2 dyn/cm force between wires 1 cm apart, and working through the CGS-to-SI conversion yields exactly 10 A.
Who was Jean-Baptiste Biot and why does he have a current unit?
Biot was a French physicist (1774–1862) who co-discovered the Biot–Savart law in 1820, describing how electric current generates a magnetic field in space. This was one of the foundational results linking electricity to magnetism. The CGS community honored him by naming their electromagnetic current unit after him.
Does anyone still use the biot in modern physics?
Essentially no. Even theorists who prefer CGS units typically use Gaussian units rather than pure CGS-EMU. The biot appears mainly in textbook conversion tables, historical physics papers, and graduate-level electrodynamics courses that teach multiple unit systems for pedagogical reasons.
How do I convert between biots and amperes?
Multiply biots by 10 to get amperes; divide amperes by 10 to get biots. A 30 A circuit carries 3 Bi; a 0.5 Bi current is 5 A. It is one of the simplest unit conversions in physics — just move the decimal point one place.
What is the Biot-Savart law and how does it relate to the biot unit?
The Biot-Savart law calculates the magnetic field produced by a small segment of current-carrying wire at any point in space. In CGS-EMU, it uses biots for current and gauss for the field. In SI it uses amperes and teslas. The law itself is fundamental — it is used to design MRI magnets, motors, and particle accelerators.
ESU of current – Frequently Asked Questions
Why is the ESU of current so absurdly small compared to an ampere?
The ESU system was designed to make Coulomb's electrostatic law simple (no constants), which means its charge unit (the statcoulomb) is tiny relative to the coulomb. Since current is charge per time, the statampere inherits that smallness. One ampere is about 3 billion statamperes — the speed of light (in cm/s) divided by 10 shows up in the conversion.
What is a statampere and is it the same as an ESU of current?
Yes, the statampere and the ESU of current are exactly the same unit: approximately 3.336 × 10⁻¹⁰ A. "Statampere" is the named form; "ESU of current" is the descriptive form. The "stat-" prefix comes from "electrostatic," just as "ab-" prefix in the EMU system comes from "absolute."
What role did the ESU system play in the discovery that light is electromagnetic?
When Weber and Kohlrausch measured the ratio of ESU to EMU charge in 1856, they got a number suspiciously close to the speed of light — about 3×10¹⁰ cm/s. Maxwell realized this was no coincidence: it meant electromagnetic disturbances propagate at light speed, proving light itself is an electromagnetic wave. A unit conversion exercise led to one of the greatest discoveries in physics.
What practical problem did the ESU system solve for 19th-century telegraph engineers?
Telegraph cables behaved like long capacitors — charge stored along the line distorted signals over transatlantic distances. The ESU system, built around Coulomb's law, made capacitance calculations straightforward: no permittivity constants, just geometry and charge. William Thomson (Lord Kelvin) used ESU-based analysis to diagnose and fix signal distortion on the first transatlantic telegraph cables in the 1860s.
Why were electrostatic and electromagnetic measurements historically done in separate labs?
Electrostatic experiments (rubbing rods, Leyden jars, spark gaps) involved high voltages and tiny charges, while electromagnetic work (coils, galvanometers, telegraph lines) involved low voltages and large currents. The equipment, techniques, and even the physicists were different. Each community built units natural to their measurements — ESU for electrostatics, EMU for electromagnetics — and it took decades after Maxwell to unify them into one coherent SI framework.