Electric and magnetic fields
They are a form of radiation produced where electricity is used or naturally present. Electric fields are created by differences in voltage, magnetic fields are created when electric current flows. An electric field will exist even when there is no current flowing; if current does flow, the strength of the magnetic field will vary with power consumption but the electric field strength will be constant. The term "emf" is also used for "electromotive force" which is the energy per unit electric charge (measured in volts) that is imparted by an energy source, such as an electric generator or a battery.