If the focal length of objective and eye lens are `1.2 cm` and `3 cm` respectively and the object is put `1.25cm` away from the objective lens and the final image is formed at infinity. The magnifying power of the microscope is

Options

A. 200
B. 100
C. 400
D. 150

Answer

A

Explanation

Given : `f_(0)=1.2cm, f_(e)=3.0cm`
`u_(0)=1.25cm, M_(oo)=?`
From `(1)/(f_(0))=(1)/(v_(0))-(1)/(u_(0)) rArr (1)/(1.2)=(1)/(v_(0))-(1)/((-1.25))`
`rArr" "(1)/(v_(0))=(1)/(1.2)-(1)/(1.25)rArr v_(0)=30cm`
Magnification at infinity,
`M_(oo)=-(v_(0))/(u_(0))xx(D)/(f_(e))=(30)/(1.25)xx(25)/(3)`
`(because D=25cm" least distance of distinct vision")=200`
Hence the magnifying power of the compound microscope is 200