An object is placed at 4 cm from the first focus of a non-equiconvex lens and its real image is form

Question

An object is placed at 4 cm from the first focus of a non-equiconvex lens and its real image is formed at 16 cm from the second focus. The focal length of the lens is

Professor PC Thomas Classes · Answer

$f^2=x_1 x_2$ where $x_1$ and $x_2$ are the distance of the object and image measured from the foci $F_1$ and $F_2$ of the lens. $ 	herefore \quad f=\sqrt{(4)(16)}=8 \mathrm{~cm} $