Seems to be almost a textbook task from a freshmen class. But I am truly puzzled.

Electromagnet has a coil of tightly wound 100 turns of copper wire around a cylinder core with relative permeability of 600. Size of the core is : width (diameter) 30mm, length 10mm (wire wound around it's wide diameter, it is wider than long). Voltage applied 12v resulting in measured current 0.2A - this should make the wire fully defined for the purpose of solving this problem. For simplicity sake number of the wire layers can be ignored.

How to go about finding field intensity and flux density ?

  • \$\begingroup\$ Is this applied voltage a DC or AC voltage? \$\endgroup\$
    – G36
    Apr 14, 2018 at 17:51
  • \$\begingroup\$ please consider DC. When it eventually comes to AC PWM I'll replace it with RMS value according to duty cycle. \$\endgroup\$ Apr 14, 2018 at 19:35

1 Answer 1


I am not sure that this model is practical as the coil would be a single layer of 42 awg wire (7.06e-5 meters dia. compared to the iron core of 30mm) and the mmf is about only 20 amp-turns. The flux density in the core is a maximum of .009 tesla at the od and .003 near the center. The field is a maximum of .005 tesla very near the core but diminishes rapidly away from the core.

I modeled this in Finite Element Analisys (FEA) software. I don't know of a reliable equation for solving this inductor because the flux densities vary widely depending upon location in the core or field. Incidently, 0.2 amps is too high to run in 42 awg wire continuously.


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