Question

A concave lens always gives a virtual image. In optical lenses worn by humans which of the following statements is true ?

• A. The lens can never be concave.
• B. In some cases the lens can be concave if the focal length is much larger than 2.5 cm.
• C. All focal length concave lenses are possible
• D. All focal length convex lenses are possible.

Answer 1

The correct option is B In some cases the lens can be concave if the focal length is much larger than 2.5 cm.

In optical lens (for eye defects) concave lens is used focal length must be much larger than 2.5 cm if it is equal or less than 2.5 cm then it means that the power point is at approximately 2.5 cm, which is not possible.