d) Why must both the objective and the eyepiece of a compound microscope have short focal lengths ?

Explanation

(d) Angular magnification of eye-piece is `[(25//f_(e) ) + 1] ( f_(e)" in cm")` which increases if `f_(e)` is smaller. Further, magnification of the objective is given by
`(v_(0))/(|u_(0)|)=(1)/((|u_(0)|//f_(0))-1)`
which is large when `|u_(0)|` is slightly greater than `f_(0)` . The microscope is used for viewing very close object. So `|u_(0)|` is small, and so is `f_(0)`.