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

Options

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

Answer

D

Explanation

Given, v=-75cm
u=-25cm
We know that, lens formula we have
`(1)/(f)=(1)/(v)-(1)/(u)`
`(1)/(f)=(-1)/(75)+(1)/(25)`
`(1)/(f)=(1)/(25)-(1)/(75)`
`(1)/(f)=(3-1)/(75)`
`(1)/(f)=(2)/(75)`
Focal length of a glass, `f=(75)/(2)=37.5cm`