Addition chain

The equation for the magnetic flux in a magnetic circuit, sometimes known as Hopkinson's law, is:

$\mathcal{ℱ}=\mathrm{\Phi }\mathcal{ℛ}$

where Φ is the magnetic flux and $\mathcal{ℛ}$ is the reluctance of the magnetic 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: ℱ = NI
                   where N is no of turns in the coil,
                         I is electric current through the circuit

     2: ℱ = Φℛ
                   where Φ is magnetic flux
                         ℛ is reluctance

     3: ℱ = Hl
                   where H is magnetizing force
                         l is mean length of solenoid, circumference of toroid

References

• The Penguin Dictionary of Physics, 1977, ISBN 0-14-051071-0

• A textbook of ELECTRICAL TECHNOLOGY,2008,ISBN 81-219-2440-5