A man with normal near point`(25cm)`reads abook with small print using a magnifyin g a thin convex lens of focal length`5cm` (a).What is the closet and fastest distance at which he can read the book when viewing through the magnifying glass ?(b)Wha tis the maximum and minimum`MP`possible using the above simple microscope?

Explanation

As for normal eyes and near point are`oo` and`25`cm resepctively ,so far magnifier`v_(max)=-oo and v_(min)=-25cm`.However ,for a lens as
`(1)/(v)-(1)/(u)=(1)/(f)`
`i.e,u=(f)/((f//v)-1)`
so u will be minimum when `v=min=-25`
`(u)_(min)=(5)/(-(5//25)-1)=-(25)/(6)=-4.17cm`
And u will be maximum when `v-max=oo`
SO the closest and fastest distance of the book from the magnifier (or eye) for clear viewing are`4.17cm and 5cm` respectively
So (b) As in case of simple magnifier `MP=(D//u)`.so`MP` will be minimum when u=max=5cm
`i.e, MP_(min)=(-25)/(-5)=5 [=(D)/(f)]`
And `MP` will be maximum when `u=min=(25//6)cm`
`MP_(max)=(25)/(-(25//6))=6[-1+(D)/(f)]`