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. 150
B. 200
C. 250
D. 400

Answer

B

Explanation

When final image is formed at infinity, then magnifying power
`M_(oo)=-(v_(o))/(u_(o))xx(D)/(f_(e ))`
From, `(1)/(f_(o))=(1)/(v_(o))-(1)/(u_(o))`
`(1)/(+1.2)=(1)/(v_(o))-(1)/((-1.25))`
`rArr " " v_(o)=30 cm`
`therefore " " |M_(oo)|=(30)/(1.35)xx(25)/(3)=200`