Watt per volt to Gilbert
W/V
Gi
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
1 W/V (Watt per volt) → 1.2566366121077 Gi (Gilbert) Just now |
Quick Reference Table (Watt per volt to Gilbert)
| Watt per volt (W/V) | Gilbert (Gi) |
|---|---|
| 0.1 | 0.12566366121077 |
| 1 | 1.2566366121077 |
| 5 | 6.2831830605385 |
| 10 | 12.566366121077 |
| 20 | 25.132732242154 |
| 100 | 125.66366121077 |
About Watt per volt (W/V)
The watt per volt (W/V) equals one ampere, derived from the power relationship P = IV rearranged as I = P/V. A device consuming 60 W at 120 V draws 0.5 W/V = 0.5 A. The W/V form is most useful when calculating branch currents from known power ratings and supply voltages — for appliance load calculations, transformer secondary currents, or power budget analysis on a circuit board. Numerically identical to the ampere, it provides an alternative view emphasising the power-per-volt character of current and is common in power electronics and electrical installation design.
A 100 W light bulb on a 230 V supply draws approximately 0.43 W/V. A 60 W laptop adapter at 20 V delivers 3 W/V to the device.
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 The gilbert is obsolete but historically significant in transformer design, relay engineering, and magnetic circuit analysis dating from the late 19th century through the 1960s.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.
Watt per volt – Frequently Asked Questions
Why would an electrician think in watts per volt?
When sizing circuits, electricians know the appliance power (watts from the nameplate) and the supply voltage (120 V or 230 V). Dividing watts by volts gives the current in amps — which is what determines wire gauge and breaker size. "1,800 W ÷ 120 V = 15 A, so I need a 20 A circuit" is daily electrician math.
Is watts per volt ever written on any product label?
No — product labels list watts, volts, and amps separately. The W/V expression lives in textbooks and engineering calculations. But every time you read "1,500 W, 120 V" on a space heater and mentally divide to get 12.5 A, you are computing watts per volt without calling it that.
Does the watts-per-volt calculation work for AC power?
Only approximately. For AC, real power (watts) = V × I × power factor. So I = W / (V × PF). A motor rated at 1,000 W with a power factor of 0.85 on 230 V actually draws 1,000 / (230 × 0.85) = 5.1 A, not the 4.35 A that simple W/V would suggest. Always account for power factor in AC circuits.
How does watts per volt help with USB power delivery calculations?
USB PD negotiates voltage levels (5 V, 9 V, 15 V, 20 V) and maximum power (up to 240 W). Dividing the negotiated power by voltage gives the cable current: 100 W at 20 V = 5 A, requiring a 5 A rated cable. At 5 V the same 100 W would need 20 A — which is why PD uses higher voltages.
What is the relationship between watts per volt and Ohm's law?
From P = IV and V = IR, you get I = P/V = V/R = P^(1/2)/R^(1/2). The W/V form is just one of many equivalent expressions for current. Which one you use depends on what you know: power and voltage gives W/V, voltage and resistance gives V/R (Ohm's law directly).
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.