Magnetic Circuits:

A magnetic circuit could be compared along with an electric current in that EMF, or voltage, generates a current flow. An ampere-turns (NI), or the magnetomotive force (F_m or mmf), will produce a magnetic flux Φ show in the Figure.  The mmf could be compared along with EMF and the flux ( ) could be compared to current.  Equation (1-16) is the mathematical representation of magnetomotive force derived by using Ohm's Law, I= E/ R.

Φ =   F_M/R = mmf/R                        (1-16)

where

Φ =   magnetic flux, Wb

Fm = magnetomotive force (mmf), At

R  = reluctance,     At/Wb

Figure: Magnetic Current with Closed Iron Path

Equation (1-17) is the mathematical representation for reluctance.

R = L/µA                                           (1-17)

Where

R = reluctance, At/Wb

L = length of coil, m

µ = permeability of magnetic material (T-m)/At

A = cross sectional area of coil, m²

Example: A coil has a reluctance of 3 x 10⁶ At/Wb and an mmf of 600 At, Find out the total flux      .

Solution:

 Φ = mmf/R

 Φ = 600At/ 3 x 10⁶   At/Wb = 200 x 10^-6   Wb = 200µWb