Question

A lady uses $+1.5\text{D}$ glasses to have normal vision from $25\text{cm}$ onwards. She uses a $20\text{D}$ lens as a simple microscope to see an object. The maximum magnifying power if she uses the microscope together with her glass is (Integer only)

Answer 1

Magnifying power of a simple microscope is given by:

$m=1+\frac{D}{f}$

It is given that when the lady uses $1.5\text{D}$ glasses then her least distance of distinct vision becomes $25\text{cm}$.

$\Rightarrow D=25\text{cm}\text{with her glass}$

$\therefore m=1+\frac{25}{f}$

$\text{Here,}\frac{1}{f}=20\text{D}$

$\Rightarrow m=1+20\times 25\times {10}^{-2}=6$

Correct Answer$:6$

Note : The focal length used in the magnification formula is the focal length of the lens used as a simple microscope.