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What is the full form of EMF

EMF: Electromotive Force

EMF stands for Electromotive Force. The electrical action generated by a non-electrical source, expressed in volts, is referred to as electromotive force in the fields of electromagnetism and electronics. Batteries, which transform chemical energy into electrical energy, or generators, are examples of devices (referred to as transducers) that produce an EMF (which converts mechanical energy). When describing electromotive force, a comparison to hydraulic pressure is occasionally utilised.

EMF Full Form

The electromagnetic energy that would be performed on an electric charge (in this case, an electron) if it travelled once around the loop is known as the EMF in electromagnetic induction. When a two-terminal device (such as an electrochemical cell) is viewed as a Thévenin's equivalent circuit, the equivalent EMF may be computed as the voltage between the two terminals. The instrument may produce an electric current if an external circuit is attached to the terminals, making it the voltage source for that circuit.


Electrochemical cells, thermoelectric gadgets, solar cells, photodiodes, power generators, transformers, and even Van de Graaff generators are examples of equipment that may produce EMF. When magnetic field variations pass through a surface in nature, EMF is produced. An electrical grid, for instance, experiences currents when the Earth's magnetic field shifts during a geomagnetic storm because the magnetic field's lines move and cross the conductors.

By turning accumulated chemical energy into electromagnetic potential energy, chemical activities at the electrodes of a battery create the charge difference that leads to a potential difference (voltage) between the terminals. You might imagine a voltaic cell having an atomically scaled "charge pump" at each electrode.

A voltage differential between the generator terminals results from electromagnetic induction when a time-varying magnetic field inside the generation system produces an electric field. As electrons go from one terminal to the next within the generator, charge separation happens. In the scenario of an open circuit, an electric field arises but prevents further charge separation. Due to charge separation, the electrical voltage balances out the EMF. This voltage has the ability to drive current if a load is connected. Faraday's law of induction is the basic principle guiding the EMF in these electrical devices.


Alessandro Volta used the phrase "electric motor force" in 1801 "to speak of the battery's active component (which he had designed around 1798)". This is now referred to as the "electromotive force" in English.

In 1830, Michael Faraday discovered that the voltaic cell's "seat of EMF" is created by chemical processes occurring at each of the two electrode-electrolyte interfaces. This means that, contrary to what was previously believed, the reactions that drive the current are not a limitless source of energy. Charge separation proceeds in the open-circuit scenario until the electrical field created by the segregated charges is adequate to stop the reactions. Years ago, Alessandro Volta incorrectly believed that contact solely (without considering a chemical reaction) was the genesis of the electromagnetic field.

Notation and Units of Measurement

Electromotive force is frequently represented by the symbol ℰ (called Summation or Sigma).

If an electric charge Q travels through a device with no internal resistance and obtains energy W, the total emf for that instrument is the energy obtained per coulomb of charge or W/Q. EMF uses the SI unit of a volt, or a joule per coulomb, like other measurements of power per charge.

The statvolt, which is equivalent to one erg per electrostatic charge unit in the centimetre-gram-second system of measurements, measures electromotive force in electrical units.

Potential Difference

An EMF is another name for an electrical potential difference. In consideration of the difference between EMF and the potential it produces, the following examples show the more formal usage:

  1. Electrical potential does not contribute to the total EMF for a circuit as a whole, such as one with a resistor connected in series with a voltaic cell, because there is no potential difference when a course is completed (Kirchhoff's voltage law is an example). The battery's chemistry alone is responsible for the EMF, which results in charge separation and an electrical voltage that powers the current.
  2. The EMF in a circuit with an electrical generator driving current via a resistor arises purely from the generator's time-varying magnetic field, producing an electrical potential difference that goes to the wind (the applied electrical voltage and the ohmic IR drop are calculated as 0).
  3. The origin of the word "transformer emf" may be seen where a transformer connecting two circuits is treated as a source of the electromotive force for one of the circuits, just as if it were created by an electrical generator.
  4. Similar to a battery, a photodiode or solar cell can be considered an EMF source that produces electrical voltage through charge separation powered by light instead of a chemical reaction.
  5. Thermopiles, fuel cells, and thermocouples are other EMF-producing devices.

When there is an open circuit, the electric charge separated by the emf-producing mechanism produces an electric field that opposes the mechanism for separation. For instance, when the opposite electric fields at each electrode are strong enough to halt the reactions, the chemical process in a voltaic cell comes to an end. In so-called reversible cells, a stronger opposing field can turn around processes.

When the device is not connected to a load, the separated electric charge generates an electric voltage difference that, in many instances, may be measured between the device's terminals with a voltmeter. The EMF itself cannot be directly measured using the external potential difference when the cell charges or discharges since some voltage are dissipated inside the source. However, if the internal resistance 'r' has previously been measured and the current 'I' and potential difference 'V' have been determined, the equation 'ℰ = V + Ir' may be deduced.

Potential difference differs from induced electromagnetic field (often called "induced voltage"). The route we travel from point A to point B has no bearing on the potential difference-the difference in the electric scalar potential-between the two sites. The voltmeter's location would be irrelevant if it consistently assessed the voltage difference between A and B. If a time-dependent magnetic field is applied, it is feasible that the measurement made by a voltmeter between locations A and B will depend on the voltmeter's position.

Consider, for instance, an indefinitely long solenoid that generates a changing flux inside of itself using an AC. Two resistors are wired in a circle around the solenoid outside of it. They are linked at the top & bottom at points A and B. The resistor on the left is 100 ohms, while the resistor on the right is 200 ohms. According to Faraday's law, the induced voltage is V, and the current is I = V/(100 + 200). The potential difference across the 100-Ohm load resistance and the 200-Ohm resistor are, respectively, 100 I and 200 I due to the two resistors' connections on both ends, but V(AB) is evaluated with the voltmeter towards the left of the solenoid, and V(AB) noted with the voltmeter to the right of the solenoid, and they are not the same.


Voltaic Cells

Around 1792, Volta invented the voltaic cell, which he first demonstrated on March 20, 1800. Volta accurately recognised the function of diverse electrodes in creating the voltage, but he wrongly discounted the electrolyte's potential contribution. "That is to say, in a sequence such that any one in the listing becomes positive when in touch with any one that succeeds, but negative by interaction with any one that precedes it," said Volta when he arranged the metals in a "tension series". A shared symbolic convention in a circuit diagram (-||-) would include a long electrode one and a small electrode 2 to signify that electrode 1 dominates. According to Volta's rule about opposing electrode EMFs, ten electrodes (such as zinc and nine other elements) may be combined to make 45 different kinds of voltaic cells (10 × 9/2).

Electromagnetic Induction

The creation of a rotating electric field by a time-varying magnetic field is known as electromagnetic induction. The motion of a magnet about a circuit, the motion of a circuit in relation to some other circuit (at least one of which must be conducting an electric current), or altering the electric current in a stationary circuit can all result in a time-dependent magnetic field.

According to Faraday's law of induction, the electromagnetically induced EMF for a particular circuit is solely governed by the rate at which the magnetic flux flows through the circuit.

Every time the flux connections change, an EMF is generated in the coil or conductor. There are two different sorts of modifications, depending on how they are made: Static induction occurs when a conductor is moved inside a static magnetic field to alter the flux linkage. The electromotive force generated by motion is also referred to as motional EMF. When the variation in flux linkage originates from a shift in the magnetic field surrounding the fixed conductor, the EMF is dynamically induced. Transformer EMF is a common name for the electromotive force produced by a magnetic field that changes over time.

Contact Potentials

Thermodynamic equilibrium dictates that one of the solids assumes a larger electrical potential than others when solids of two distinct materials are in contact. The term "contact potential" refers to this approach. What is sometimes referred to as a Contacting EMF or Galvani potential is created when dissimilar metals come into contact. The magnitude of the potential difference between two solids at charge neutrality is commonly stated as a difference between their individual Fermi levels, where the Fermi level (another name for the chemical potential of an energy functional) specifies the energy necessary to remove an electron from a body and transfer it to a common location (such as ground).

Such a transfer will take place if there is an energy benefit to moving an electron from one element to the other. One body gains electrons from the transfer, while the other loses electrons, resulting in charge separation. A voltage differential between the bodies as a result of this charge transfer partially cancels the potential resulting from the contact, and equilibrium is finally established.

The EMF is the initial variance in Fermi levels that existed before contact. Because a charge transfer would occur if a continuous current were to be driven through a load connected to the contact potential's terminals, the steady current is not possible. Once equilibrium is reached, there is no mechanism to maintain this transfer and, thus, a current.

Why does the contact potential not count as one of the potential drop contributions in Kirchhoff's law of voltages? The conventional response is that each circuit comprises a specific junction or diode, and all contact potentials are caused by wire and other factors surrounding the circuit. Since all the contact potentials add up to zero, Kirchhoff's law allows for their disregard.

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