99 Percentile Qs Bank for JEE MainPhysicsRay Optics
A plano-convex lens of focal length 10   cm is silvered at its plane face. The distance d at which an object must be placed in order to get its image on itself is
Options
- A5   cm
- B20   cm
- C10   cm
- D2 . 5   cm
Correct answer
C. 10   cm
Step-by-step solution
If the object and the image coincide in the shown combination in the question, it will behave like a converging mirror. So, applying mirror formula to the combination 1 f = 1 v + 1 u     . . . 1 where, u ,   v are the positions of the object and image, respectively and f is the focal length. Here, u = v = - d , Hence, substituting in equation ( 1 ) , 1 f = 1 - d + 1 - d = - 2 d For the combination, 1 f = 2 f l + 1 f m     . . . 2 where, f l ,   f m are the focal lengths of the lens and