The focal length of objective and eye lens of a microscope are `4 cm` and `8 cm` respectively. If the least distance of distinct vision is `24 cm` and object distance is `4.5 cm` from the objective lens, then the magnifying power of the microscope will be

Options

A. 18
B. 32
C. 64
D. 20

Answer

B

Explanation

For objective lens,
`(1)/(f_(o))=(1)/(v_(o))-(1)/(u_(o))`
or `(1)/(4)=(1)/(v_(o))-(1)/((-4.5))rArr |v_(o)|=36 cm`
`therefore` Magnifying power, `|M|=(v_(o))/(u_(o))(1+(D)/(f_(e )))=(36)/(4.5)(1+(24)/(8))=32`