A small object is placed on the principal axis of concave spherical mirror of radius `20 cm` at a distance of `30 cm.` By how much will the position of the image alter only after mirror, when a parallel-sided slab of glass of thickness `6 cm` and refractive index `1.5` is introduced between the centre of curvature and the object? The parallel sides are perpendicular to the principal axis.

Answer

A, C, D

Explanation

Case1 `1/v+1/u=1/f`
`:. 1/(v_1)-1/30=1/(-10)`
`:. v_1=-15 cm`
CaseII Shift `=(1-1/mu)t=(1-1/1.5)6=2 cm`
`:. 1/(v_2)-1/28=1/(-10)`
`:. v_2=-15.55 cm`
`:. Deltav=0.55 cm`