Question

An object is 3cm in front of a convex lens with 2cm focal length.

Find: a) the image distance

B)the magnification.

C)the image description: real or virtual? erect or inverted?

Answer 1

Given:

$d_o=3\:\rm cm$

$f=-2\:\rm cm$

The thin lens equation says

$$\frac{1}{d_0}+\frac{1}{d_i}=\frac{1}{f}$$

Hence:

a) the image distance

$$d_i=\frac{fd_o}{d_o-f}=\frac{-2*3}{3-(-2)}=-1.2\:\rm cm$$

b) the magnification

$$m=-\frac{d_i}{d_0}=0.4$$

c) virtual, direct.