Question

A point object O is placed in front of a concave mirror of focal length 10 cm. A glass slab of refractive index μ = 3/2 and thickness 6 cm is inserted between object and mirror. Find the position of final image when the distance x shown in figure is 

(a) 5 cm

(b) 20 cm

Answer 1

As we have read in the above article the normal shift produced by a glass slab is,

for the mirror the object is placed at a distance (32 - Δx) = 30 cm from it. Applying mirror formula

(a) When x = 5 cm : The light falls on the slab on its return journey as shown. But the slab will again shift it by a distance Δx = 2 cm. Hence, the final real image is formed at a distance (15 + 2) = 17 cm from the mirror.

(b) When x = 20 cm : This time also the final image is at a distance 17 cm from the mirror but it is virtual as shown.