Question

The convex lens used in a simple microscope produces a magnification of 5. The image is formed at the least distance of distinct vision. What is the focal length of the lens?

• A. 6.25 cm
• B. 4.25 cm
• C. 10.25 cm
• D. 5.85 cm

Answer 1

The correct option is A 6.25 cm

Given magnification $m=5$

Image is formed at least distance of distinct vision (i.e., $D=25cm)$

$\therefore m=1+\frac{D}{f}$

$5=1+\frac{25cm}{f}$

$4=\frac{25cm}{f}$

$f=\frac{25}{4}cm=6.25cm$