Question

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

Answer 1

Answer: (C)

$\frac{25}{9}$cm

Answer 2

$m = m_{o} \times m_{e} \Rightarrow m = m_{o} \times \left( 1 + \frac{D}{f_{e}} \right)$

$\Rightarrow 100 = 10 \times \left( 1 + \frac{25}{f_{e}} \right) \Rightarrow f_{e} = \frac{25}{9}\mspace{6mu} cm$