Question

A person suffering from myopia cannot see clearly beyond 1 m. What should be the focal length of the concave lens that will correct his vision?

• A. 1 m
• B. 2 m
• C. 4 m
• D. 0.5 m

Answer 1

The correct option is A

1 m

The rays coming from a point at a distance of 1 m from the eye, are focused on the retina. Parallel rays, after passing through the concave lens, should appear to come from that point. By the definition of the focus of a concave lens, the point is the focus of the concave lens used. So, the focal length of the concave lens should be 1 m.