An object is placed 21 cm in fron of a concave mirror of radis of curvature 20 cm.A glass slab of thicknes 3 cm and refractive index 1.5 is palced close to the mirror in the space between the object and the mirror. Find the position of the final image fromed. The distance of the nearer surface of the slab from the mirror is 10 cm.

Explanation

Shift by slab x = `d (1- (1)/(mu)) = 3(1- (1)/(1.5)) = 1"cm"`
for image formed by mirror `u= -(21-1) "cm" = -20"cm"`.

`(1)/(u) + (1)/(v) + (1)/(f) implies (1)/(-20) + (1)/(v) = (1)/(-10) implies v = -20"cm"`
shift in the direction of light `v - (20+1) = -21"cm"`.