Lenses are constructed by a material of refractive index 1.50. The magnitudes of the radii of curvature are 20 cm and 30 cm. Find the focal lengths of the possible lenses with the above specifications.

Refractive index ==1.5

Magnitudes of the curvature are = 20 cm and 30 cm

Lens makers’ formula:

There are 4 types of possible lens:

Case1: biconvex lens:

Case 2: biconcave lens;

Case 3: concave – concave lens:

Case 4: convex-convex lens: