A bulb is located on a wall. Its image is to be obtained on a parallel wall with the help of convex

Question

A bulb is located on a wall. Its image is to be obtained on a parallel wall with the help of convex lens. The lens is placed at a distance $d$ ahead of second wall, then required focal length will be\

Professor PC Thomas Classes · Answer

(b) : A real image is to be formed on the $2^{	ext {nd }}$ wall of the bulb placed on the first wall by the convex lens. The lens is placed at a distance of $d$ from the $2^{	ext {nd }}$ wall.\ Now, we know that to form a real image of an object on a screen by a convex lens, the distance between the source and the screen $(D)$ should be equal to $4 f$, where $f$ is the focal length of the lens.\ In that case, $u=v=D / 2=d$.\ $	herefore \quad f=D / 4=d / 2$\