Question

A person is suffering from both near sightedness and far sightedness. His spectacles would be made of

• A. Two convex lenses with the upper lens having a larger focal length than the lower lens.
• B. Two concave lenses with the upper lens having a smaller focal length than the lower lens.
• C. A concave lens as the upper lens and a convex lens as the lower lens.
• D. A convex lens as the upper lens and a concave lens as the lower lens.

Answer 1

Answer: (C)

A concave lens as the upper lens and a convex lens as the lower lens.

A person suffering from myopia (near-sightedness) can see only nearby objects clearly and it is corrected by using a concave lens. Whereas a person suffering from hypermetropia (long-sightedness) can see only distant objects clearly and it is corrected by using a convex lens.

Thus if a person suffers from both, then he must be using a concave lens to see distant objects and a convex lens to see nearby objects (especially for reading). Hence his spectacles would be made of a concave lens as the upper lens and convex lens as the lower lens.