NOTE: This is not a homework problem, so do not shift it. The question is as follows, I am given a core having an air gap wounded by a coil, I am given area of core, gap. Length of core and gap. number of turns. Permeability of core and air gap and magnetic field in the core (I assume no leakage flux too) And I am required to find the inductance of the coil used. I had a formula L = N^2*MuCore*MuO*AreaCore/lengthCore I used it and got wrong answer. I realized that probably this formula was derived assuming no air gaps and that is why I got the answer wrongly. I changed to the formula L=N*Flux/Current and got the answer correctly (in fact book I am following also uses the same approach) But I realize that the formula L = N*Flux/Current was derived using the value of inductance written above (assuming that there is no air gap) So how does this time the new formula works? According to me L = N^2*MuCore*MuO*AreaCore*AreaGap/(LenCore*AGap + LGap*ACore) (answer seems to be wrong using above formula too) Any help is appreciated.