What is normal shift and apparent shift

what is normal shift and apparent shift

1.Apparent shift:

The Apparent shift of the ray is the perpendicular distance between the incident and the emergent ray with reference to refraction of light through a glass slab.

2.Normal Shift (NS):

During refraction, the apparent shift in the position of the object along the normal is called normal

Consider denser medium ABCD of refractive index n1 and depth �t� surrounded by another medium of refractive index n2; assuming that (1) is denser and medium (2) is rarer like air.

NS= t [ 1 - n2/n1 ]

Apparent shift = Object distance from refracting surface � image distance from refracting surface.

?y (apparent shift) t = 1 - ?-1 where t is the object distance and ? = ?1/ ?2
� If there are a number of slabs with different refractive indices placed between the observer and the object.
Total apparent shift = ??yi