Let us consider two solenoids A and B, made from same magnetic material of relative permeability μ_r and equal area of cross-section. Length of A is…

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