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