Question

An object is placed perpendicular to the principal axis of concave lens of focal length 30 cm. Find the position of an image when the object is at a distance 20 cm from the lens.Solve the given problem.(Ans: v = -12 cm)

Answer 1

Focal length(f) = 30 cm. (negative)

Object distance(u) = 20 cm. (negative)

Using the Lens Formula,

1/f = 1/v - 1/u

⇒ 1/-30 = 1/v - 1/-20

⇒ 1/v = 1/-30 + 1/-20

⇒ 1/v = 3/-60

⇒ v = -20 cm.

Hence, the image is formed at the distance of 20 cm on the same side of the lens.

Hope it helps.