what is  the formula for  finding lateral displacement?

 When a ray of light is incident obliquely on a parallel sided glass slab the emergent ray shifts laterally. The perpendicular distance between the direction of the incident ray and emergent ray is called "Lateral displacement" or“lateral shift’’.  

Lateral shift is directly proportional to the thickness of slab. The relation is,

Where,

d=lateral displacement,

t=thickness of slab,

r=angle of refraction.