A point object O is placed at a distance of `20 cm` from a convex lens of focal length `10 cm` as shown in the figure. At what distance x from the lens should a convex mirror of focal length `60 cm,` be placed so that final image coincide with the object?

Options

A. 10cm
B. 15cm
C. 20 cm
D. final image can never coincide with the object in the given conditions

Answer

C

Explanation

`(1)/(v)- (1)/(20)= (1)/(10) implies v = 20 "cm"`
`therefore` R for mirror = 2f = `2 xx 60 = 120 "cm"`
`therefore x = 20 +R = 20 + 120 = 140 "cm"`