Electromagnetic coil

Either an electric current is passed through the wire of the coil to generate a magnetic field, or conversely, an external time-varying magnetic field through the interior of the coil generates an EMF (voltage) in the conductor.

[3] The advantage of using the coil shape is that it increases the strength of the magnetic field produced by a given current.

Conversely, a changing external magnetic flux induces a voltage in a conductor such as a wire, due to Faraday's law of induction.

[3][4] The induced voltage can be increased by winding the wire into a coil because the field lines intersect the circuit multiple times.

[3] The direction of the magnetic field produced by a coil can be determined by the right hand grip rule.

The end of a magnetic core from which the field lines emerge is defined to be the North pole.

[5] The hole in the center of the coil is called the core area or magnetic axis.

The winding is often wrapped around a coil form made of plastic or other material to hold it in place.

These are coils used to translate time-varying magnetic fields to electric signals, and vice versa.

The magnetic field lines ( green ) of a current-carrying loop of wire pass through the center of the loop, concentrating the field there
In a coil of multiple turns of wire the magnetic field of the turns adds in the center of the coil, creating a strong field. This drawing shows a cross section through the center of the coil. The crosses are wires in which current is moving into the page; the dots are wires in which current is emerging from the page.
Diagram of typical transformer configurations
Field coil electromagnet on the stator of an AC universal motor .
Canon AF-10 Date old camera shutter driver coil.
Transformer
The sensor coil of a metal detector .