A ray of light passes through four transparent media with refractive index n1, n2, n3 and n4 as shown. The surfaces of all media are parallel
If the emergent ray DE is parallel to incident ray AB, then1
n1 = n4
2
n2 = n4
3
n3 = n4
4
\({n_1} = \frac{{{n_2} + {n_3} + {n_4}}}{3}\)