A convex lens, of focal length 30 cm, a concave lens of focal length 120 cm, and a plane mirror are arranged as shown. For an object kept at a distance of 60 cm from the convex lens, the final image, formed by the combination, is a real image, at a distance of:

Step-by-step solution

From lens formula for convex lens, we have 1 f = 1 v - 1 u ⇒ 1 30 = 1 v + 1 60 ⇒ 1 60 = 1 v Applying lens formula to concave lens, we have 1 f = 1 v - 1 u ⇒ 1 - 120 = 1 v - 1 40 ,   ∵ u = + 40   cm ⇒ v = 60   cm Virtual object 10 cm behind plane mirror. Hence real image 10 cm in front of mirror. Hence 60 cm from convex lens.