so, i'm taking up a course on electrical machine design and our professor gave us the equations for computing the different values required for a given specification. here is my problem: given these two equations: laD^2 = (W/N)(6.079x10^8)/(Byqr) --> eq. 1 and la = pi(D)(r)/(pK) --> eq. 2 where la = length of armature core (inches) D = diameter of armature core (inches) r = ratio of pole arc to pole face By = air gap density W = output of armature (watts) N = speed p = number of poles K = some constant ranging from 0.667 to 1 equation 1 came from W = Z*Ec*Ic where Z = total number of armature conductors Ec and Ic = voltage and current on the conductor Ec = 6.45(Bg)(la)(pi)(D)(r)(N)/60x10^8 where Bg = average flux density in the air gap under each pole (gauss) and Ic = q(pi)(D)/Z where q = specific loading substituting all Ec and Ic in W you can get equation 1. and then you can solve for D by combining the two equations. my question is where does the second equation came from??