A point light source is kept in front of a convex mirror at a distance of 40 cm. The focal length of the mirror is 40 cm. Find the position of image.

u = 40 cm (negative)

f = 40 cm (positive)

Mirror formula:

⇒ – 1\over u + 1\over v = 1\over 40

⇒ 1\over v = 1\over 40 + 1\over u

⇒ 1\over v = 2\over 40

⇒ 1\over v = 1\over 20

⇒ v = 20 cm

Hence, the image is formed 20 cm behind the mirror.