Explain lateral shift for the refraction from rectangular glass slab.

Explanation

For a rectangular slab, refraction takes place at two interfaces (air-glass and glass-air).
It is easily seen from figure that `r_2 = i_1`. i.e., the emergent ray is parallel to the incident ray there is no deviation but it does suffer lateral displacement/shift with respect to the incident ray.
Here, emergent ray is parallel to incident ray hence `i_1=r_2`. Thus, there is no deviation of incident ray but it experiences the lateral shift as compared to incident ray.
For more information :
If lateral shift is x, then
`x=txxi_2(1-n_1/n_2)`
where t = thickness of slab
`n_1` = refractive index of rarer medium (air)
`n_2` = refractive index of denser medium (glass)
`i_1` = incidence angle