WBJEE 2014 Physics Solved Paper

A glass slab consists of thin u iform layers of progressively decreasing refractive indices RI (see figure) such that theRI of any layer is μ-mΔμ. Here μ and Δμ denote the RI of 0th layer and the difference in RI between any two consecutivelayers, respectively. The integer m = 0, 1, 2, 3..... denotes the numbers of the successive layers. A ray of light fromthe 0th layer enters the 1st layer at an angle of incidence of 30°. After undergoing the mth refraction, the ray emergesparallel to the interface. If μ = 1.5 and Δμ = 0.015, the value of m is