An object is located on a wall, its image of equal size is to be obtained on a parallel wall with the help of a convex lens. The lens in placed at a distance ' d ' in front of the second wall. The required focal length of the lens is

Step-by-step solution

Size of the image is equal to the size of the object. Hence image distance will be equal to object distance. Also if object distance u=2 f , Image distance will be 2 f . aligned & u = v = d =2 f & u + v =2 ~d =4 f & f = d 2 aligned