Question

The near vision of an average person is 25 cm. To view an object with an angular magnification of 10, what should be the power of the microscope?

Answer 1

It is given, that least distance of distinct vision of an average person (i.e., D) is 25 cm, in order to view an object with magnification 10,

Here, v = D = 25 cm and u = f

But the magnification ${\displaystyle m=\frac{v}{u}=\frac{D}{f}}$

⇒ ${\displaystyle f=\frac{D}{m}=\frac{25}{10}}$ = 2.5 cm = 0.025 m

But power ${\displaystyle P=\frac{1}{f(\text{in} m)}=\frac{1}{0.025}}$ = 40 D

This is the required power of lens.