# Magnetic circuit

**Hopkinson's lawMagnetic Circuitsair gapOhm's law for magnetic circuits**

A magnetic circuit is made up of one or more closed loop paths containing a magnetic flux.wikipedia

118 Related Articles

### Magnetic field

**magnetic fieldsmagneticmagnetic flux density**

Magnetic circuits are employed to efficiently channel magnetic fields in many devices such as electric motors, generators, transformers, relays, lifting electromagnets, SQUIDs, galvanometers, and magnetic recording heads.

The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits.

### Magnetomotive force

**MMF**

Similar to the way that electromotive force (EMF) drives a current of electrical charge in electrical circuits, magnetomotive force (MMF) 'drives' magnetic flux through magnetic circuits.

In physics, the magnetomotive force (mmf) is a quantity appearing in the equation for the magnetic flux in a magnetic circuit, often called Ohm's law for magnetic circuits.

### Electromagnet

**electromagnetselectro-magnetelectromagnetic**

Magnetic circuits are employed to efficiently channel magnetic fields in many devices such as electric motors, generators, transformers, relays, lifting electromagnets, SQUIDs, galvanometers, and magnetic recording heads. The flux is usually generated by permanent magnets or electromagnets and confined to the path by magnetic cores consisting of ferromagnetic materials like iron, although there may be air gaps or other materials in the path.

In many practical applications of electromagnets, such as motors, generators, transformers, lifting magnets, and loudspeakers, the iron core is in the form of a loop or magnetic circuit, possibly broken by a few narrow air gaps.

### Magnet keeper

**keeper platekeeperkeepers**

A magnet keeper, also known historically as an armature, is a bar made from soft iron or steel, which is placed across the poles of a permanent magnet to help preserve the strength of the magnet by completing the magnetic circuit; it is important for magnets that have low magnetic coercivity, such as alnico magnets (0.07T).

### Magnetic reluctance

**reluctancemagnetic reluctancesmagnetic resistance**

where \mathcal{F} is the magnetomotive force (MMF) across a magnetic element, \Phi is the magnetic flux through the magnetic element, and \mathcal{R} is the magnetic reluctance of that element.

Magnetic reluctance, or magnetic resistance, is a concept used in the analysis of magnetic circuits.

### John Hopkinson

**HopkinsonHopkinson, JohnJohn Hopkinson, the physicist**

This law is often called Hopkinson's law, after John Hopkinson, but was actually formulated earlier by Henry Augustus Rowland in 1873.

Hopkinson's law, the magnetic counterpart to Ohm's law, is named after him.

### Magnetic flux

**fluxfluxes definition of flux used in electromagnetism**

where \mathcal{F} is the magnetomotive force (MMF) across a magnetic element, \Phi is the magnetic flux through the magnetic element, and \mathcal{R} is the magnetic reluctance of that element. A magnetic circuit is made up of one or more closed loop paths containing a magnetic flux.

### Permeance

The inverse of reluctance is called permeance.

A magnetic circuit almost acts as though the flux is conducted, therefore permeance is larger for large cross-sections of a material and smaller for longer lengths.

### Inductor

**inductorscoilinductive**

In practice this equation is used for the MMF of real inductors with N being the winding number of the inducting coil.

A higher magnetic field and inductance can be achieved by forming the core in a closed magnetic circuit.

### Gyrator–capacitor model

**Magnetic capacitancegyrator-capacitor modelMagnetic reactance**

This relationship is part of an electrical-magnetic analogy called the gyrator-capacitor model and is intended to overcome the drawbacks of the reluctance model.

The gyrator–capacitor model - sometimes also the capacitor-permeance model - is a lumped-element model for magnetic fields, similar to magnetic circuits, but based on using elements analogous to capacitors (see magnetic capacitance) rather than elements analogous to resistors (see magnetic reluctance) to represent the magnetic flux path.

### Ohm's law

**ohmicOhmohmic losses**

In electronic circuits, Ohm's law is an empirical relation between the EMF \mathcal{E} applied across an element and the current I it generates through that element.

### Magnetic complex reluctance

Magnetic complex reluctance (SI Unit: H −1 ) is a measurement of a passive magnetic circuit (or element within that circuit) dependent on sinusoidal magnetomotive force (SI Unit: At·Wb −1 ) and sinusoidal magnetic flux (SI Unit: T·m 2 ), and this is determined by deriving the ratio of their complex effective amplitudes.[Ref.

### Pickup (music technology)

**pickuppickupsguitar pickup**

Reluctance can also be applied to variable reluctance (magnetic) pickups.

### Electric motor

**motorelectric motorsmotors**

Magnetic circuits are employed to efficiently channel magnetic fields in many devices such as electric motors, generators, transformers, relays, lifting electromagnets, SQUIDs, galvanometers, and magnetic recording heads.

### Electric generator

**generatorgeneratorselectrical generator**

Magnetic circuits are employed to efficiently channel magnetic fields in many devices such as electric motors, generators, transformers, relays, lifting electromagnets, SQUIDs, galvanometers, and magnetic recording heads.

### Transformer

**power transformerelectrical transformerprimary winding**

### Relay

**relayslatching relayelectric relay**

### SQUID

**superconducting quantum interference devicesuperconducting quantum interference devicesDC SQUID**

### Galvanometer

**D'Arsonval galvanometertangent galvanometernull detector**

### Recording head

**record headheadheads**

### Magnet

**permanent magnetmagnetspermanent magnets**

The flux is usually generated by permanent magnets or electromagnets and confined to the path by magnetic cores consisting of ferromagnetic materials like iron, although there may be air gaps or other materials in the path.

### Electromotive force

**EMFelectromotive force (EMF)ℰ**

Similar to the way that electromotive force (EMF) drives a current of electrical charge in electrical circuits, magnetomotive force (MMF) 'drives' magnetic flux through magnetic circuits. In electronic circuits, Ohm's law is an empirical relation between the EMF \mathcal{E} applied across an element and the current I it generates through that element.

### Magnetic monopole

**magnetic monopolesmagnetic chargemonopole**

The MMF represents the potential that a hypothetical magnetic charge would gain by completing the loop.