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

Here `P_(1)=1.5 D`: d = 25 cm `P_(2) = 20 D` (a) With glasses
Focal length of glasses,
`f_(1)=(100)/(P_(1))=(100)/(1.5)=(200)/(3)cm`
u=-25cm,v= ?
As `(1)/(v)-(1)/(u)=(1)/(f_(1))`
`therefore` `(1)/(v)=(1)/(f_(1))+(1)/(u)=(3)/(200)=(1)/(25)=(3-8)/(200)=(5)/(200)`
v=-40cm
`M=1+(d)/(f_(2))=1+(40)/(100//20)=9`
(b) Without glasses
`M=1+(d)/(f_(2)=1+(25)/(100//20)=6`