inductance for magnetic core..
<-- Length----->
__ __ __
___________\ \___\ \___\ \_______
_______ \ \ \ \ \ \________
| \ \ \ \ \ \ |
| \ \ \ \ \ \ Core |<-Area
|_____\ \___\ \___\ \______|
\_\ \_\ \_\
Number
L_H = mu_r*mu_0_Area*Number^2/Length;
mu_0 = 4*pi*1E-7_H/m