Lateral shift through parallel slab (t = d sin(i−r)/cos r)

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t = d sin(i−r)/cos r

What each symbol means

SymbolWhat it stands for
dThickness of parallel-sided slab (m)
iAngle of incidence at first surface (from normal)
rAngle of refraction inside slab (from normal)
tLateral shift of emergent ray relative to incident line (m)

When to use this

Standard JEE / NCERT assumptions unless stated (paraxial, thin lens, coherent YDSE sources, etc.).