Question

the distance between a convex lens and plane mirror is 10 cm. the parallel rays incident on the convex lens after reflection from the mirror form an image at the optical centre of the lens.find the focal length of the lens.

Answer 1

$$\begin{gathered} Weknowlensformula,\frac{1}{f}=\frac{1}{v}-\frac{1}{u} \\ thedis\tan cebetweenlensandtheplanemirroris10cm. \\ theimagedis\tan cefromthelensisv=0,afterreflectionfromthemirror. \\ Sou=-10cm \\ puttingthesevaluesintheformulaoflens, \\ \frac{1}{f}=\frac{1}{0}-\frac{1}{-10} \\ orf=10cm.1/0meansimageisformingatinfinityafterreflection. \end{gathered}$$