Electrical Engineering ⇒ Topic : Magnetomotive force (m.m.f.).

Gaurav
 
Magnetomotive force (m.m.f.). lt is that force which drives or tends to drive the flux through a magnetic circuit. In short it is written as m.m.f. It is the product of number of turns (N) and current (I) in amperes in those turns, i.e., m.m.f. = Nl  
 
Sunita
 
MAGNETOMOTIVE FORCE (mmf) Consider a ring specimen of a conductor of mean radius r having a winding of N turns which are wound uniformly as shown in Fig. (1). Let the current in
FIGURE (1) Magnetic flux due to current ring in a coil having N turns the winding be I A. Then, the product of the current (I) and the number of turns on the winding (N) is known as the magnetomotive force (mmf) of the circuit,i.e. m.m.f = NI. The mmf in the magnetic circuit is analogous to the emf in the electric circuit. Emf in an electric circuit is responsible for the flow of current. But in a magnetic circuit mmf is responsible for the existence of flux in the magnetic medium. This mmf acts along the magnetic line of force whose length is l = 2 π r. Also the magnetic field intensity (H)= mmf/unit length NI/l where lis the mean length of the magnetic path. The above result can also be obtained using Ampere's circuit law, as below.  
 
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