Toroid (electromagnetism)

A toroid is a ring-shaped coil, often wound around a magnetic core, that produces a magnetic field largely confined within the ring.

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Ampère's circuital law: A law relating the magnetic field integrated around a closed path to the electric current enclosed by that path. A circular Amperian path inside an ideal toroid makes its field straightforward to calculate.
Electric current: The rate at which electric charge passes through a cross-section of a conductor. Current through the winding creates the toroid’s magnetic field.
Toroidal inductor: An inductor made with a winding arranged around a ring-shaped magnetic core. It is the common circuit component built from a toroidal coil.
E-core: A magnetic core shaped like the letter E, commonly paired with an I-shaped piece to form a magnetic circuit. Its openable core assembly contrasts with a toroid’s continuous ring.
Magnetic field: A physical field produced by electric currents and magnetic materials that exerts forces on moving charges and magnetic dipoles. The toroid’s geometry shapes where its magnetic field is concentrated.
Electromagnetic induction: The production of electromotive force by changing magnetic flux through a circuit. Changing current in a toroid changes its flux and induces voltage in its winding.
Toroidal transformer: A transformer whose primary and secondary windings are arranged around a ring-shaped core. Its closed core path supports efficient coupling with relatively low external leakage.
Pot core: A cup-shaped magnetic core that encloses a coil to reduce stray fields. It confines flux with an enclosing shell rather than a ring-shaped winding path.
Magnetic permeability: A measure of how a material responds to and supports a magnetic field. A high-permeability core strengthens the field produced by a given coil current.
Inductance: A circuit property that relates changing current to induced electromotive force and magnetic flux linkage. A toroid’s field geometry and core determine its inductance.