Definition and Concept of Electromotive Force
– Electromotive force (emf) is the conversion of other forms of energy into electrical energy.
– Emf is not a physical force but rather a potential difference that drives electric charges.
– ISO/IEC standards have deprecated the term ’emf’ in favor of ‘source voltage’ or ‘source tension’.
– An electronic-hydraulic analogy compares emf to the mechanical work done to water by a pump, resulting in a pressure difference.
– Emf can be defined as the electromagnetic work done on an elementary electric charge traveling around a closed loop of a conductor.
Devices that Generate Electromotive Force
– Electrochemical cells, thermoelectric devices, solar cells, photodiodes, and electrical generators can provide emf.
– Magnetic field fluctuations can induce emf in electrical grids during geomagnetic storms.
– Batteries achieve charge separation through chemical reactions, converting chemical potential energy into electromagnetic potential energy.
– Voltaic cells can be thought of as having a charge pump that moves positive charges from low potential to high potential.
– Electrical generators create an electric field via electromagnetic induction, resulting in a potential difference between terminals.
Historical Background of Electromotive Force
– Alessandro Volta introduced the term ‘force motrice électrique’ in 1801 to describe the active agent of a battery.
– Michael Faraday established that chemical reactions at electrode-electrolyte interfaces provide the seat of emf for voltaic cells.
– Volta’s earlier opinion that contact alone was the origin of emf was proven incorrect.
– Faraday’s law of induction governs the emf in electrical machines.
– The term ‘electromotive force’ is the English translation of Volta’s original term.
Notation and Units of Measurement for Electromotive Force
– Electromotive force is often denoted by the symbol ‘E’.
– In a device without internal resistance, the net emf is the energy gained per unit charge passing through the device.
– The SI unit for emf is the volt, equivalent to a joule per coulomb.
– Electromotive force in electrostatic units is measured in statvolts.
– The emf in an open-circuit case can be mathematically expressed as the difference in electric scalar potential between two terminals.
Relationship of Electromotive Force with Voltage and Magnetic Flux
– Emf and voltage are related but not the same phenomenon.
– The induced emf in a loop is not a voltage in the sense of a difference in electric scalar potential.
– The self inductance of a loop and the magnetic flux determine the emf in a coil.
– The emf in a coil can be localized to a specific region, known as an inductor.
– The emf in a loop can be calculated using the line integral of the electric field along the conductor and the center line. Source: https://en.wikipedia.org/wiki/Electromotive_force
In electromagnetism and electronics, electromotive force (also electromotance, abbreviated emf, denoted or [citation needed]) is an energy transfer to an electric circuit per unit of electric charge, measured in volts. Devices called electrical transducers provide an emf by converting other forms of energy into electrical energy. Other electrical equipment also produce an emf, such as batteries, which convert chemical energy, and generators, which convert mechanical energy. This energy conversion is achieved by physical forces applying physical work on electric charges. However, electromotive force itself is not a physical force, and ISO/IEC standards have deprecated the term in favor of source voltage or source tension instead (denoted ).
An electronic–hydraulic analogy may view emf as the mechanical work done to water by a pump, which results in a pressure difference (analogous to voltage).
In electromagnetic induction, emf can be defined around a closed loop of a conductor as the electromagnetic work that would be done on an elementary electric charge (such as an electron) if it travels once around the loop.
For two-terminal devices modeled as a Thévenin equivalent circuit, an equivalent emf can be measured as the open-circuit voltage between the two terminals. This emf can drive an electric current if an external circuit is attached to the terminals, in which case the device becomes the voltage source of that circuit.
Although an emf gives rise to a voltage and can be measured as a voltage and may sometimes informally be called a "voltage", they are not the same phenomenon (see § Distinction with potential difference).
