An object is placed on the principal axis of convex lens of focal length 10 cm as shown. A plane mirror is placed on the other side of lens at a distance of 20 cm . The image produced by the plane mirror is 5 cm inside the mirror. The distance of the object from the lens is ____ cm .

Step-by-step solution

Given here: Focal length of convex lens, f = 10   cm Now, as seen in figure, image from lens is formed at point I 1 , whose location is 5   cm from mirror. Thus, I 1 is at 15   cm from lens. Using lens equation, we have 1 v - 1 u = 1 f Putting the value, 1 15 - 1 - u = 1 10 ⇒ 1 u = 1 10 - 1 15 ⇒ u = 10 × 15 10 - 15 Thus, object is placed at 30   cm from lens.