Question

A biology student uses a simple magnifier to examine the structural features of an insect's wing. The wing is held 3.95 cm in front of the lens, and the image is formed 25.0 cm from the eye. (a) What is the focal length of the lens?

Answer 1

$f = \frac{1}{\frac{1}{x}- \frac{1}{x`}} = \frac{1}{\frac{1}{3.95}- \frac{1}{25}} = 4.69 \;cm$