Magnetomotive force

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In physics, the magnetomotive force is a quantity appearing in the equation for the magnetic flux in a magnetic circuit, sometimes known as Hopkinson's law:

 \mathcal{F} = \Phi \mathcal{R} ,

where Φ is the magnetic flux and is the reluctance of the circuit. It can be seen that the magnetomotive force plays a role in this equation analogous to the voltage V in Ohm's law: V = IR.

Magnetomotive force is analogous to electromotive force, emf (= difference in electric potential, or voltage, between the terminals of a source of electricity, e.g., a battery from which no current is being drawn) since it is the cause of magnetic flux in a magnetic circuit; i.e.,

  1. = NI
    where N is the number of turns in the coil and
    I is the electric current through the circuit
  2. = Φℛ
    where Φ is the magnetic flux and
    is the reluctance
  3. = Hl
    where H is the magnetizing force (the strength of the magnetizing field) and
    l is the mean length of a solenoid or the circumference of a toroid

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