Basic Electrical Theory MAGNETISMExample 3: The 20 cm coil used in Example 1 with the same current is now wound aroundan iron core 40 cm in length. Find the field intensity.Solution:N = 80, I = 6A, and NI = 480 AtH480 At0.4 m1200 AtmNote that field intensity for Examples 2 and 3 is the same.Figure 25 Different Physical Forms of ElectromagnetsReluctanceOpposition to the production of flux in a material is called reluctance, which corresponds toresistance. 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 inequation (1-15).(1-15)RmmfFReluctance 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
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