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In electromagnetism and electronics, electromotive force (also electromotance, abbreviated emf, [1] [2] denoted ) is an energy transfer to an electric circuit per unit of electric charge, measured in volts. Devices called electrical transducers provide an emf [3] by converting other forms of energy into electrical energy. [3]
Lorentz force on a charged particle (of charge q) in motion (velocity v), used as the definition of the E field and B field. Here subscripts e and m are used to differ between electric and magnetic charges. The definitions for monopoles are of theoretical interest, although real magnetic dipoles can be described using pole strengths.
where is back EMF, is the constant, is the flux, and is the angular velocity. By Lenz's law, a running motor generates a back-EMF proportional to the speed. Once the motor's rotational velocity is such that the back-EMF is equal to the battery voltage (also called DC line voltage), the motor reaches its limit speed.
If ΔΦ B is positive, the direction of the emf is the same as that of the curved fingers (yellow arrowheads). If ΔΦ B is negative, the direction of the emf is against the arrowheads. [22] It is possible to find out the direction of the electromotive force (emf) directly from Faraday’s law, without invoking Lenz's law.
An EMF meter is a scientific instrument for measuring electromagnetic fields (abbreviated as EMF). Most meters measure the electromagnetic radiation flux density (DC fields) or the change in an electromagnetic field over time (AC fields), essentially the same as a radio antenna, but with quite different detection characteristics.
The magnetic field strength depends on the magnitude of the electric current, and therefore follows any changes in the magnitude of the current. From Faraday's law of induction, any change in magnetic field through a circuit induces an electromotive force (EMF) in the conductors, a process known as electromagnetic induction. This induced ...
Magnetic field must be strong enough to fully saturate the samples (or else inaccurate measurements will be taken) Magnetic field must be uniform across the sample space (otherwise the addition of field gradients [5] [7] will induce force that alter the vibration once again leading to inaccurate results
That is, the back-EMF is also due to inductance and Faraday's law, but occurs even when the motor current is not changing, and arises from the geometric considerations of an armature spinning in a magnetic field. This voltage is in series with and opposes the original applied voltage and is called "back-electromotive force" (by Lenz's law).