A man with normal near point (25cm) reads a book with small print using a magnifying glass a thin convex lens of focal length 5cm. a) What is the closest and farthest distance at which he can read the book when viewing through the magnifying glass? b) What is the maximum and minimum magnifying power possible using the above simple microscope?

A man with normal near point (25cm) reads a book with small print usin

1.	A man with normal near point (25cm) reads a book with small print using a magnifying glass a thin convex lens of focal length 5cm. a) What is the closest and farthest distance at which he can read the book when viewing through the magnifying glass? b) What is the maximum and minimum magnifying power possible using the above simple microscope?
Answer» Solution :A for normal eye FAR and near points are `infty` and 25CM respectively so for magnifier `v_(max)=- infty and v_(mi N)=-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 =-25cm i.e., `(u)_(mi n)=5/(-(5//25)-1)=-25/6=-4.17 CM` and u will be maximum when v=max= `infty` i.e., `(mu)_(max)=5/((5/infty)-1)=-5cm` So the closest and farthest distances of the book from the magnifier (or eye) for clear viewing are 4.17cm and 5cm respectively b) As in case of simple magnifier `MP=(D//u)`. So MP will be minimum when u=max=5cm i.e, `(MP)_(mi n)=(-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]`