Magnetic Circuits and Induction

What are reluctance and permeance in the magnetic circuits? Derive their expressions in any type of magnetic circuits.

An iron ring of mean length 1.2 m and cross sectional area of 0.005 m² is wound with a coil of 900 turns. If a current of 2 A in the coil produces a flux density of 1.2 T in the iron ring, calculate: i) The mmf ii) Total Flux in the ring iii) The magnetic field strength iv) The relative permeability of iron at this flux density.

Define the term magneto motive force and magnetizing force for magnetic circuit. A ring has mean diameter of 21 cm and a cross sectional area of 10 cm². The ring is made up of semicircular section of cast iron and cast steel, with each joint having a reluctance equal to an air gap of 0.2 mm. Find the ampere turns required to produce a flux of 0.8 mWb. The relative permeability of cast steel and cast iron are 800 and 166 respectively.