Magnetomotive Force
How to Convert Ampere-turns to Gilberts
To convert from Ampere-turns (A·t) to Gilberts (Gi), you use the conversion factor that 1 Gilbert is approximately 0.79577 A·t. Therefore, to convert A·t to Gi, you divide by this factor.
Example:
Convert an MMF of 100 A·t to Gilberts.
100 A·t / 0.79577 ≈ 125.66 Gi
Answer: 100 Ampere-turns is equal to approximately 125.66 Gilberts.
The Driver of Magnetism: Understanding Magnetomotive Force
Magnetomotive force, or MMF, is the property in a magnetic circuit that produces a magnetic field. It is the magnetic analogue of electromotive force (EMF) or voltage in an electrical circuit. Just as voltage is the 'pressure' that drives an electric current through a resistance, magnetomotive force is the 'pressure' that drives magnetic flux through a magnetic reluctance. MMF is the phenomenon that gives rise to a magnetic field. In most practical applications, this force is generated by passing an electric current through a coil of wire.
The strength of the magnetomotive force is directly proportional to both the number of turns of wire in the coil and the magnitude of the electric current flowing through it. Doubling the current or doubling the number of turns in the coil will double the MMF. This principle is the foundation of all electromagnets, from small relays in electronic circuits to the massive superconducting magnets used in MRI machines and particle accelerators. Understanding MMF is essential for engineers and physicists who design and analyze magnetic circuits, transformers, electric motors, and other electromagnetic devices. The standard unit is the Ampere-turn, which directly reflects how MMF is created.
Relevant Formulas in Science and Mathematics
- Definition of MMF (Physics): For a coil, the magnetomotive force (Fₘ) is given by
Fₘ = NI, where 'N' is the number of turns of wire in the coil and 'I' is the electric current in Amperes. - Magnetic Circuit Law (Ohm's Law for Magnetism): This law relates MMF (Fₘ), magnetic flux (Φ), and magnetic reluctance (Rₘ):
Fₘ = ΦRₘ. This is analogous to Ohm's Law (V = IR). - Relationship to H-field: MMF is the line integral of the magnetic field strength (H-field) around a closed loop:
Fₘ = ∮ H ⋅ dl. This is a more general statement of Ampere's Law.
A Deep Dive into Common Magnetomotive Force Units
- Ampere-turn (A·t or A): This is the standard SI unit for magnetomotive force. It is often simply written as 'Amperes' as the 'turns' part is a dimensionless quantity, but 'Ampere-turn' is more descriptive. An MMF of 1 A·t is produced by a current of 1 Ampere flowing through a single loop of wire.
- Gilbert (Gi): The Gilbert is the unit of magnetomotive force in the older CGS (centimeter-gram-second) system of units. It is named after the English physician and natural philosopher William Gilbert, who was a pioneer in the study of magnetism. One Gilbert is approximately 0.79577 Ampere-turns. This unit is now largely obsolete but may be found in older texts on magnetism.