A plano convex lens of material of refractive index $\mu_1$ exactly fits into a plano concave lens of…
A plano convex lens of material of refractive index $\mu_1$ exactly fits into a plano concave lens of material of refractive index $\mu_2$. If $R$ is the radius of curvature of the curved surfaces of the lenses and the plane surfaces of the lenses are parallel, the focal length of the combination is