Gilbert to Milliampere
Gi
mA
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
1 Gi (Gilbert) → 795.77499999999604699 mA (Milliampere) Just now |
Quick Reference Table (Gilbert to Milliampere)
| Gilbert (Gi) | Milliampere (mA) |
|---|---|
| 0.1 | 79.5774999999996047 |
| 0.5 | 397.88749999999802349 |
| 1 | 795.77499999999604699 |
| 2 | 1,591.54999999999209398 |
| 5 | 3,978.87499999998023494 |
| 10 | 7,957.74999999996046988 |
| 100 | 79,577.49999999960469877 |
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 The gilbert is obsolete but historically significant in transformer design, relay engineering, and magnetic circuit analysis dating from the late 19th century through the 1960s.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 Milliampere (mA)
The milliampere (mA) equals one thousandth of an ampere (10⁻³ A) and is the practical unit for most consumer electronics and lighting circuits. USB 2.0 ports supply up to 500 mA; USB-C Power Delivery can reach 5,000 mA (5 A). A standard 5 mm indicator LED operates at 10–20 mA; mid-power LED drivers supply 100–350 mA. Human perception of electric shock begins near 1 mA; currents above 10 mA cause involuntary muscle contraction, and above 100 mA can be lethal. Wireless sensors, earphones, and small motors typically draw single-digit to low-hundreds of milliamperes.
A USB 2.0 port provides up to 500 mA for charging. A standard 5 mm indicator LED operates at around 20 mA.
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.
Milliampere – Frequently Asked Questions
How many milliamps is dangerous to a human?
The danger thresholds for 50/60 Hz AC are roughly: 1 mA (tingling), 10–20 mA (muscle lock — you cannot let go), 75–100 mA (ventricular fibrillation), and 200+ mA (cardiac arrest and burns). DC is somewhat less dangerous at the same current. Duration matters enormously — 100 mA for 1 second is more lethal than 100 mA for 10 ms.
Why is my phone charger rated in milliamps when it charges at 2 amps?
Battery capacity is rated in milliampere-hours (mAh), not milliamps. A 4,000 mAh battery holds 4,000 mA for one hour (or 2,000 mA for two hours). The charger delivers 2 A (2,000 mA) of current, and it takes about 2 hours to fill that 4,000 mAh battery from empty.
What is the milliamp draw of common household items?
A wireless earbud draws 5–15 mA during playback. A TV remote uses about 10 mA when pressing a button. An LED nightlight consumes 20–50 mA. A smoke detector in standby draws 10–30 μA (0.01–0.03 mA) — so low it runs on a 9V battery for years.
Why do LED specifications always mention 20 mA?
Standard 5 mm indicator LEDs were designed around a 20 mA operating point — bright enough to see clearly, low enough to avoid overheating the tiny die. All datasheet specs (luminous intensity, color, forward voltage) are measured at this "test current." High-power LEDs use 350 mA or 700 mA as their reference instead.
How does milliamp-hour (mAh) relate to milliamp (mA)?
Milliamp-hours measure charge capacity; milliamps measure current flow rate. A 2,000 mAh battery can deliver 2,000 mA for 1 hour, or 200 mA for 10 hours, or 20 mA for 100 hours — current times time equals capacity. Dividing mAh by mA gives approximate runtime in hours.