An electromagnetic coil is a conductor of electricity that is in the shape of a coil, spiral, or helix, a series of wires wound around a core. It is used in devices where electric current interacts with a magnetic field (EMF). The coil design and shape enhance the strength of the magnetic field. The current from the coil generates a magnetic field. In cases where there is a time varying magnetic field, the interior of the coil has an EMF in the conductor.
When determining the direction of the magnetic field from a coil, the right hand, coffee mug, corkscrew, or right thumb rule is used, where the fingers represent the direction of the magnetic field lines of force, and the thumb, pointed upward, is the current. This same example can be used to determine the orientation and direction of the magnetic field.
The conducting material for an electromagnetic coil is wire, which is referred to as the winding. In the center of the coil is the core, magnetic axis, around which the wire is wound or looped. Though a core is not necessary for an electromagnetic coil, having one increases the strength of the field. The individual loops are a turn. Turns are insulated with a nonconductive material to keep them from passing current. Each end of the wrapped wire is left open and exposed to be attached to the circuit.
The strength of a coil is determined by the number of turns of wire, the number of wound wires, and the core. There are several varieties of cores made from metals or plastic. Four common cores types are iron, ferrite, toroidal, and laminated.
It is possible for any conductor to create a magnetic field around a conductor in accordance with Ampere’s Law. The coil shape significantly increases the strength of the magnetic field produced by the current. The strength of the field is further enhanced by increasing the number of windings around the core, which is an inductive or magnetic coupling.
In an inductively coupled winding, a time varying current applied to the outer winding produces a time varying winding in the other windings. The winding where the varying current is first applied is referred to as the primary, while the other windings are the secondary ones. This configuration is called a transformer.
An electromagnetic coil is an inductor that stores energy and is a passive electrical component since it has no gain and cannot control the flow of energy. Its purpose is to oppose changes in a circuit and block alternating current (AC), while letting direct current (DC) through. If there is a rapid rise in the flow of current, the electromagnetic field of an inductor inhibits and prevents the increase.
The most common form of an electromagnetic field is an inductor, which are found in radios to control interference and keeping it from being transmitted. In a transformer, two or more inductors are placed together to create overlapping magnetic fields.