Question

Magnification of a compound microscope is $30$. Focal length of eyepiece is $5\, cm$ and the image is formed at a distance of distinct vision $25\, cm$. The magnification of the objective lens is :

• A. 6
• B. 5
• C. 7.5
• D. 10

Answer 1

Answer: (B)

5

Answer 2

The image formed in a microscope at least distance of distinct vision
(D = $25\, cm$ ) has magnification
$M=M_{o} \times M_{e}$
where My is magnification of objective lens and $M_{e}$ that of eyepiece.
Also, $M=M_{o}\left(1+\frac{D}{f_{e}}\right)$
Given, $f_{e}=5\, cm,\, D=25\, cm,\, M=30$
$\therefore 30=M_{o} \times\left(1+\frac{25}{5}\right)$
or $M_{o}=\frac{30}{6}=5$