Electromagnetic Induction

Let us consider two solenoids \(A\) and \(B\), made from same magnetic material of relative permeability \(\mu_r\) and equal area of cross-section. Length of \(A\) is twice that of \(B\) and the number of turns per unit length in \(A\) is half that of \(B\). The ratio of self inductances of the two solenoids, \(L_A: L_B\) is