A plano convexlensfits exactly into a plan » concave lens. Their plane surfaces are parallel to each other. If lenses are madeofdifferent materials of refractive indices j1, and po and R is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is:

A

$$\frac{2R}{(\mu_{2}-\mu_{1})}$$

B

$$\frac{R}{2(\mu_{1}+\mu_{2})}$$

C

$$\frac{R}{2(\mu_{1}-\mu_{2})}$$

D

$$\frac{R}{(\mu_{1}-\mu_{2})}$$