Basic Electrical Theory
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.
N = 80, I = 6A, and NI = 480 At
Note that field intensity for Examples 2 and 3 is the same.
Figure 25 Different Physical Forms of Electromagnets
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
Reluctance is related to magnetomotive force, mmf, and flux, F, by the relationship shown in
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.