Question

You're using a convex lens with f = 10.0 cm to study an insect. How far from the insect should you hold the lens to get an upright image magnified by a factor of 19? Express your answer to two significant figures and include the appropriate units.

Answer 1

Image being upright for a convex lens implies that it is a virtual image.

$f = 10 cm$

Since the magnification $M = v/u=-1.9$

$v = -1.9\times u$

where f is the focal length, v is the image distance and u is the objecct distance. Substituing in the lens formula,

$\frac{1}{u}+\frac{1}{v}=\frac{1}{f}$

Substituing and solving, we get

$u=4.74cm$