Question

If we need a magnification of `375` from a microscope of tube length `15 cm` and an objective of focal length `0.5 cm`, what focal length eye lens should be used ?

Answer 1

`M = - 375, L = 15 cm, f_(0) = 0.5 cm, f_(e) = ?, d = 25 cm`
`M = (v_(0))/(-u_(0))(1 + (d)/(f_(e)))`
As focal length of objective lens is small `u_(0) ~~ f_(0)`. Also, as focal length of eye lens is small, `v_(0) ~~ L`
`:. M = (L)/(- f_(0))(1 + (d)/(f_(e)))` `- 375 = (15)/(- 0.5)(1 + (25)/(f_(e)))`
`(25)/(f_(e)) = (375)/(30) - 1 = 11.5 f_(e) = (25)/(11.5) = 2.2 cm`