Problem 77-1    Source:   Problem created by the author of the site.

A ferromagnetic core is shown in Figure 77-01.1 whose path length average is 60 cm. There is a thin 0.05 cm air gap in the core, which is one piece in the rest. The cross-sectional area of the core is 36 cm², the relative permeability of the core is 4800 and the coil wound in the core has 240 turns through which a current of 10 A circulates. Assume that the spread in the air gap increase the effective area of the cross section by 6%. Given this information, find

a) the total reluctance of the flow path (iron plus air gap).

b) what is the magnetic flux density in the air gap?

Problem 77-4    Source:   Example 1-2 - page 17 - CHAPMAN, Sthephen J, - Book: Fundamentos de Máquinas Elétricas - 5ª edição - Ed. McGraw-Hill - 2013.

A ferromagnetic core is shown in Figure 77-04.1 whose average path length is 40 cm . There is a thin air gap of 0.05 cm in the core, which is solid in the rest. The area of the straight section of the core is 12 cm², the relative permeability of the core is 4,000 and the coil wound around the core has 400 turns . Assume that the spread in the air gap increase the effective area of the straight section by 5%. Given that information, find:

a) the total reluctance of the flow path (iron plus air gap).

b) the current required to produce a flow density of 0.5 T in the air gap.