A person is unable to see objects nearer than 50 cm. He wants to read a book placed at a distance of 25 cm. Find the nature, focal length and power of the lens he requires for his spectacles.

A person is unable to see objects nearer than 50 cm. He wants to read

1.	A person is unable to see objects nearer than 50 cm. He wants to read a book placed at a distance of 25 cm. Find the nature, focal length and power of the lens he requires for his spectacles.
Answer» Solution :This person has defect of Hypermetropia which is far SIGHTEDNESS that means the image is formed beyond the retina so it requires a convergent lens to get focused at retina. Now corrective measure is `u=-25cm` `V=-50cm` `(1)/(f)=(1)/(v)-(1)/(u)` `(1)/(f)=(1)/(-50)-(1)/(-25)` `=-(1+2)/(50)=(1)/(50)` `f=50cm` `P=(1)/(f)` `P=(100)/(50)=2D` Focal length = 50 CM. Power = 2 D