Calculate the focal length of a reading glass of a person, if the distance of distinct vision is 75cm.

Options

A. 25.6 cm
B. 37.5 cm
C. 75.2 cm
D. 100.4 cm

Answer

B

Explanation

The least distance of distinct vision for normal eyes is 25cm, if object is at `u=-25cm`, its image is formed `v=-75cm` for the defected eye.
The required focal length of reading glass.
`rArr" "(1)/(f)=(1)/(v)-(1)/(u)=(1)/(-75)+(1)/(25)`
`rArr" "(1)/(f)=(-2+6)/(150)=(4)/(150)`
`f=37.5cm`