A transformer is a passive component that transfers electrical energy from
one electrical circuit to another circuit, or multiple circuits. A varying
current in any coil of the transformer produces a varying magnetic flux in the
transformer's core, which induces a varying electromotive force (EMF) across
any other coils wound around the same core. Electrical energy can be
transferred between separate coils without a metallic (conductive) connection
between the two circuits. Faraday's law of induction, discovered in 1831,
describes the induced voltage effect in any coil due to a changing magnetic
flux encircled by the coil.