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

For objective lens `(1)/(f_(o))=(1)/(v_(o))-(1)/(u_(o))`
`implies (1)/(v_(o))=(1)/(f_(o))+(1)/(u_(o))=(1)/(4)+(1)/(-5)=(1)/(20)impliesv_(o)=20cm`
Now `M=(v_(o))/(u_(o))(1+(D)/(f_(e)))=(20)/(5)(1+(20)/(10))=12.`