<P> An electromagnetic coil is an electrical conductor such as a wire in the shape of a coil, spiral or helix . Electromagnetic coils are used in electrical engineering, in applications where electric currents interact with magnetic fields, in devices such as electric motors, generators, inductors, electromagnets, transformers, and sensor coils . 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 . </P> <P> A current through any conductor creates a circular magnetic field around the conductor due to Ampere's law . The advantage of using the coil shape is that it increases the strength of magnetic field produced by a given current . The magnetic fields generated by the separate turns of wire all pass through the center of the coil and add (superpose) to produce a strong field there . The more turns of wire, the stronger the field produced . Conversely, a changing external magnetic flux induces a voltage in a conductor such as a wire, due to Faraday's law of induction . The induced voltage can be increased by winding the wire into a coil, because the field lines intersect the circuit multiple times . </P>

When does a wire in an electric circuit generate a magnetic field
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