Reluctance

Basic Electrical Theory MAGNETISM Example 3: The 20 cm coil used in Example 1 with the same current is now wound around an iron core 40 cm in length. Find the field intensity. Solution: N = 80, I = 6A, and NI = 480 At H 480 At 0.4 m 1200 At m Note that field intensity for Examples 2 and 3 is the same. Figure 25 Different Physical Forms of Electromagnets Reluctance Opposition to the production of flux in a material is called reluctance, which corresponds to resistance. The symbol for reluctance is R, and it has the units of ampere-turns per weber (At/wb). Reluctance is related to magnetomotive force, mmf, and flux, F, by the relationship shown in equation (1-15). (1-15) R mmf F Reluctance is inversely proportional to permeability (µ). Iron cores have high permeability and, therefore, low reluctance. Air has a low permeability and, therefore, a high reluctance. Rev. 0 Page 35 ES-01