A luminous object is separated from a screen by distance d. A convex lends is placed between the object and the screeen such that it forms a distinct image on the screen. The maximum possible focal length of this convex lens is.

Options

A. 4d
B. 2d
C. `(d)/(2)`
D. `(d)/(4)`

Answer

D

Explanation

Focal length of a convex lens by displacement method is given as, `f=(a^(2)-b^(2))/(4a)`
Where, a= distance between the image and object and b=distance between two position of lens
Here, a=d and to form a distinct image b=0, so the mamimum possible focal length is d/4.