Answer
Infinity
Work Step by Step
Given:
Object distance $p=40\ cm$
Focal length of lens $f=+40\ cm$
Using the lens formula:
$\frac{1}{f}=\frac{1}{p}+\frac{1}{i}$
Where $i$ is the image distance
$\frac{1}{i}=\frac{1}{f}-\frac{1}{p}$
$\frac{1}{i}=\frac{p-f}{pf}$
$\frac{1}{i}=\frac{40-40}{40\times40}$
$\frac{1}{i}=0$
$i=∞$
Note: Since the object is placed at a distance equal to the lens’s focal length, the image will formed at infinity.
