Q. The objective lens of a compound microscope produces magnification of 10. In order to get an overall magnification of 100 when image is formed at $25\ cm$ from the eye, the focal length of the eye lens should be
A) $4\ cm$
B) $10\ cm$
C) $\frac{25}{9}cm$
D) $9\ cm$
Explanation
(c) $m = m_{o} \times m_{e} \Rightarrow m = m_{o} \times \left( 1 + \frac{D}{f_{e}} \right)$
$\Rightarrow 100 = 10 \times \left( 1 + \frac{25}{f_{e}} \right) \Rightarrow f_{e} = \frac{25}{9}cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.