EMFs

EMF is an acronym with two common meanings in physics and engineering. It can refer to electromotive force, a driving potential in circuits, or to electromagnetic fields, the electric and magnetic fields surrounding charges and currents. Context usually clarifies the intended meaning, and the two senses are connected by fundamental electrodynamics.

Electromotive force (EMF) is the work done per unit charge around a closed circuit. It is generated by chemical reactions in a battery or by induction when magnetic flux changes. In a circuit, EMF is not always equal to the terminal voltage because of internal resistance. The SI unit is the volt (V).

Electromagnetic fields describe the spatial distribution of electric and magnetic influences produced by charges and currents. The electric field is measured in volts per meter, and the magnetic field in tesla. Static fields arise from steady charges, while time-varying fields propagate as electromagnetic waves. The term EMF also appears in everyday contexts to denote exposure to such fields, for example from power lines or wireless devices.

Exposure limits for public and occupational settings are specified by safety guidelines. Standards from ICNIRP and national bodies distinguish between frequency bands and field components. Low-frequency fields from household devices are generally considered safe within limits; higher-frequency fields can cause heating at sufficient intensities.

Applications span energy conversion, electrical machines, transmission systems, and sensing. Understanding EMFs involves Faraday's law, Kirchhoff's laws, and the interaction of fields with matter. The term remains broad, and its meaning depends on the technical context.