Question

If the focal length of objective and eye lens are $1.2cm$ and $3cm$ respectively and the object is put $1.25cm$ away from the objective lens and the final image is formed at infinity. The magnifying power of the microscope is

• A. $150$
• B. $200$
• C. $250$
• D. $400$

Answer 1

Answer: (B)

$200$

$m_{\infty }=-\frac{v_0}{u_0}\times \frac{D}{f_e}$
From $\frac{1}{f_0}=\frac{1}{v_0}-\frac{1}{u_0}$
$\Rightarrow \frac{1}{(+1.2)}=\frac{1}{v_0}-\frac{1}{(-1.25)}\Rightarrow v_0=30cm$
$\therefore |m_{\infty }|=\frac{30}{1.25}\times \frac{25}{3}=200$