question_answer

A point source S is placed at a distance of 21 cm from a convex mirror of focal length 12 cm. What is the distance (in cm) of a converging lens of focal length 10 cm from mirror, placed between the source and the mirror to get the final image on the source itself-

A) 12 cm              

B) 10 cm

C) 6 cm                

D) 5 cm

Correct Answer: C

Solution :

\[\frac{1}{x+24}+\frac{1}{-(21+x)}\,\,=\,\,\frac{1}{10}\] \[x\,\,=\,\,6\,cm\]