Question

A convex lens of focal length 30 cm is kept parallel to a plane mirror at distance 15 cm from it. An object is placed at distance 60 cm from the lens. Find distance of final image from mirror.

• A. 15 cm
• B. 45 cm
• C. 30 cm
• D. 60 cm

Answer 1

Answer: (B)

45 cm

Answer 2

First, calculate the image formed by the convex lens using the lens formula. With the object at $u=-60$ cm and focal length $f=+30$ cm, the image is formed at $v=60$ cm from the lens. This image is located $60 - 15 = 45$ cm in front of the plane mirror. This image then acts as the object for the plane mirror. For a plane mirror, the image is formed as far behind the mirror as the object is in front. Therefore, the final image is formed 45 cm behind the mirror, making its distance from the mirror 45 cm.