question_answer

The distance between a convex lens and a plane mirror is 10 cm. The parallel rays incident on the convex lens after reflection from the mirror form image at the optical centre of the lens. Focal length of lens will be

A)            10 cm

B)            20 cm

C)            30 cm

D)            Cannot be determined

Correct Answer: B

Solution :

                                                              From the figure, Using property of plane mirror Image distance = Object distance               f ? 10 = 10 \[\Rightarrow f=20\text{ }cm\]