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

`f_(o)=1.2cm, f_(e)=3cm, D=+25cm`
When final image formed at infinity
`m=(v_(o))/(u_(o))((D)/(f_(e)))" …(i)"`
`(1)/(f_(o))=(1)/(v_(o))-(1)/(u_(o))`
`rArr" "(1)/(v_(o))=(1)/(f_(o))+(1)/(u_(o))=(1)/(1.2)-(1)/(1.25)=(1)/(30)`
`v_(o)=+30cm`
`m=((30)/(1.25))((25)/(3))=200`