Q- An achromatic doublet consists of a biconvex positive lens of refractive index μ_{1} in contact with a plano concave lens of refractive index μ_{2}. All curved surfaces have a radius of curvature R = 25 cm.

(a) If μ_{1red} = 1.49 what is the focal length of the biconvex lens for red light?

(b) If μ_{2red} = 1.54 what is the focal length of the plano convex lens for red light?

(c) What is the focal length of the doublet for red light?

(d) If μ_{1blue} = 1.52 what must be the value of μ_{2blue} for the combination to be achromatic?