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What Is Electromotive Force?

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  • Written By: Andrew Kirmayer
  • Edited By: Shereen Skola
  • Last Modified Date: 05 December 2014
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Electromotive Force (EMF) is the difference in voltage between the terminals of a battery, generator, thermocouple or other electrical device. It is typically defined as electrical potential energy, which allows current to pass from one end of a circuit to another. Charge differences are usually created when particles called electrons collect at one terminal and there are fewer of them at the other end. Amperes, voltage, and internal resistance are calculated mathematically to determine electromotive force, which is generally less than the total voltage of the system.

Voltaic cells often have distinct electromotive forces. These are generally triggered by chemical reactions where the surface of an electrode and an electrolytic substance meet. Induced electromotive force is commonly used at power generating facilities, and is often accomplished by using a coil or conductor. Magnetic fields and the shape of the electrical circuit also affect induction, which can be static, if the magnetic field doesn’t change, or dynamic if the field around a conductor changes.

Electrical cells made of nickel-cadmium, nickel metal-hydride, lead-acid, as well as lithium-ion can produce an electromotive force. The concept was named by Alessandro Volta, the inventor of the battery. While it first referred to the force needed to separate different charges, electromotive force was revised to characterize the strength of an electric field in the 1860s. It is typically generated by batteries, based on the placement of oppositely charge metal parts within the devices.

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A thermocouple generally has V-shaped metal components that produce an EMF when heated. Water heaters and fireplaces often work this way, while generators make use of it by coiling a wire around a magnet. Chemical and magnetic forces can have an effect, as well as mechanical and gravitational influences. Induction by means of rotors in a power building affect electromotive force, while heating and cooling elements of a thermoelectric device create a temperature difference that impacts EMF as well.

The electromotive force of a power source is often determined by the strength of external measures, based on their unit of charge. It can ultimately be defined by how this gets an electrical charge around the complete circuit, based on the use of one source. In the 21st century, technology such as nanomagnets is being combined with electromotive force in research. This could lead to magnetic sensors that are highly sensitive, as well as new varieties of batteries based on magnetic and quantum technology.

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