A person uses `+ 1.5 D` glasses to have normal vision from `25 cm` onwards. He uses a `20 D` lens as a simple microscope to see an object. Calculate the maximum magnifying power, if he uses the microscope
(a) together with his glasses
(b) without the glasses.

Explanation

First calculate near point of lady
`f =(100)/(P(D)) = (100)/(3//2) = (200)/(3)cm`
`(1)/(-(N.P.)') -(1)/(-("distance of object")) = (1)/(f)`
`(1)/(-(N.P.)') - (1)/(-25) = (1)/(200//3)`
`(1)/(-(N.P)') = (3)/(200)-(1)/(25) = (3-8)/(200)=- (1)/(40)`
`N.P' = 40cm = D'`
Maximum magnifiying power of microscope
`m=1+(D)/(f),f:` focal length of microscope lens
`f = (100)/(20) = 5cm`
(a) Together with glass `D = 25cm`
`m=1+(D)/(f) = 1+(25)/(5)=6`
(b) Without glass
`m' =1+(D')/(f) = 1+(40)/(5) = 9`