A compound microscope has an eye piece of focal length `10 cm` and an objective of focal length `4 cm`. Calculate the magnifcation, if an object is kept at a distance of `5 cm` from the objective so that final image is formed at the least distance vision `(20 cm)`

Options

A. 12
B. 11
C. 10
D. 13

Answer

A

Explanation

`f_(e) = 10 cm , f_(o) = 4 cm , u_(o) = - 5 cm , D = 20 cm `
`(1)/(v_(o)) = (1)/(f_(o)) + (1)/(u_(o)) = (1)/(4) - (1)/(5) = (5- 4)/(20) `
`v_(o) = 20 `
m `= (v_(o) )/(u_(o)) xx (1 + (D)/(f_(e)) ) = (20)/(5) (1 + (20)/(10))` = 12.