Gilbert to Biot
Gi
Bi
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
1 Gi (Gilbert) → 0.0795774999999996047 Bi (Biot) Just now |
Quick Reference Table (Gilbert to Biot)
| Gilbert (Gi) | Biot (Bi) |
|---|---|
| 0.1 | 0.00795774999999996047 |
| 0.5 | 0.03978874999999980235 |
| 1 | 0.0795774999999996047 |
| 2 | 0.1591549999999992094 |
| 5 | 0.39788749999999802349 |
| 10 | 0.79577499999999604699 |
| 100 | 7.95774999999996046988 |
About Gilbert (Gi)
The gilbert (Gi) equals 10/(4π) amperes — approximately 0.7958 A — and is the CGS-EMU unit of magnetomotive force (MMF) rather than a general-purpose current unit. In magnetic circuit analysis, MMF drives magnetic flux through a reluctance, analogously to how voltage drives current through resistance. A single-turn coil carrying 1 Gi of MMF passes 0.7958 A. In SI, magnetomotive force is measured in ampere-turns (A·T). The gilbert is obsolete but historically significant in transformer design, relay engineering, and magnetic circuit analysis dating from the late 19th century through the 1960s.
A relay coil requiring 2 Gi of MMF to actuate needs about 1.6 A·turn in SI terms. Vintage transformer and relay datasheets from the 1940s–1960s often specify MMF in gilberts.
Etymology: Named after William Gilbert (1544–1603), English physician and natural philosopher who authored De Magnete (1600), the first systematic scientific study of magnetism and electricity, establishing that the Earth itself acts as a giant magnet.
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.
Gilbert – Frequently Asked Questions
Why is the gilbert approximately 0.7958 amperes and not a round number?
The gilbert equals 10/(4π) amperes because the CGS-EMU system uses a different form of Ampere's law where the factor 4π appears explicitly rather than being absorbed into μ₀. This "unrationalised" form distributes 4π differently in the equations, producing the 1/(4π) factor when converting to SI's "rationalised" system.
What is magnetomotive force and how is it different from regular current?
MMF is the magnetic analogue of voltage — it drives flux through a magnetic circuit the way EMF drives current through an electrical circuit. For a coil, MMF = N × I (turns times current). A 100-turn coil carrying 1 A has 100 ampere-turns of MMF. In CGS, that same MMF would be about 125.7 gilberts.
Who was William Gilbert and why does he deserve a unit?
Gilbert (1544–1603) was physician to Queen Elizabeth I and author of De Magnete (1600), the first true scientific investigation of magnetism. He demonstrated that Earth is a magnet, distinguished magnetic from electrostatic attraction, and coined the word "electricus." He did all this 87 years before Newton's Principia — a genuine pioneer of experimental science.
Where would I find gilberts used today?
Practically nowhere in new designs. You might encounter gilberts in vintage relay and transformer datasheets from the 1940s–1960s, in older American and European magnetic component catalogs, or in classic electrical engineering textbooks. Any modern magnetic circuit analysis uses ampere-turns (A·T) for MMF.
How do I convert gilberts to ampere-turns?
Multiply gilberts by 10/(4π) ≈ 0.7958 to get ampere-turns. Wait — that is backwards. Multiply gilberts by 0.7958 to get amperes for a single-turn coil. For MMF conversion: 1 gilbert = 0.7958 ampere-turns. So a relay spec of 5 Gi needs about 4 ampere-turns to actuate — for instance, 4 turns at 1 A or 8 turns at 0.5 A.
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.