An optometrist prescribes a corrective lens with a power of +1.5 D. The lens maker starts with

Question:

An optometrist prescribes a corrective lens with a power of +1.5 D. The lens maker starts with a glass blank that has an index of refraction of 1.6 and a convex front surface whose radius of curvature is 20 cm. To what radius of curvature should the other surface be ground? Is the surface convex or concave?