(a) An object is seen through a simple microscope of focal length `12cm`. Find the angular magnification produced if the image is formed at the near point of the eye which is `25cm` away from it.
(b) A `10D` lens is used as a magnifier. Where shold the object be placed to obtain maximum angular magnification for a nirmal eye (near point `= 25cm)`?

Explanation

(a) `f = 12cm, D = 25 cm`
`m = 1+(D)/(f) = 1+(25)/(12) = 3.08`
(b) `P = 10 D`
`f = (100)/(P) = (100)/(10) = 10 cm`
For maximum angular magnification, image is formed at near point.
`u =- u, v =- D =- 25 cm, f = 10 cm`
`(1)/(v) - (1)/(u) = (1)/(f)`
`(1)/(-25) - (1)/(-u) = (1)/(10)`
`(1)/(u) = (1)/(10) +(1)/(25) = (5+2)/(50)`
`u = (50)/(7) cm`