The changing magnetic field induces an electromotive force (EMF) voltage in the second wire by Faraday's law of induction.The two coils may be physically contained in a single unit, as in the primary and secondary windings of a transformer, or may be separated.An inductively coupled transponder consists of a solid state transceiver chip connected to a large coil that functions as an antenna.[citation needed] Reducing low-frequency magnetic fields may be necessary when dealing with electronics, as sensitive circuits in close proximity to an instrument with a power transformer may pickup the mains frequency.Electrical distribution line engineers use inductive coupling to tap power for cameras on towers and at substations that allow remote monitoring of the facilities.