Question

A compound microscope having $f_0=7\text{mm}$, $f_e=20\text{mm}$ and distance between the lenses is $20\text{cm}$. If image is formed at least distance of distinct vision then magnifying power? Answer the magnitude of nearest integer.

Answer 1

For eyepiece
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
$-\frac{1}{25}+\frac{1}{u_e}=\frac{1}{2}$
$u_e=\left(\frac{50}{27}\right)\text{cm}$
Now
$v_0=20-\frac{50}{27}=\frac{490}{27}$
We know that
$m_0=\frac{f_0-v_0}{f_0}=-25$
Therefore
$|MP|=m_0(1+\frac{D}{f_e})=337$