Question

A man can see upto 5 metre clearly. To see clear upto 10 m, the focal length of lens will be

• A. +20 metre
• B. -5 metre
• C. +10 metre
• D. -10 metre

Hint:

For correcting vision, use the lens formula \(\frac{1}{f} = \frac{1}{v} - \frac{1}{u}\), where \(v\) is the object distance and \(u\) is the image distance.

Answer 1

The Correct Option is B

The focal length of a lens required to correct vision can be calculated using the lens formula. For a person who can only see 5 metres clearly, the lens should have a focal length of -5 metres to correct vision to 10 metres.