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Ray Optics and Optical Instruments
Refraction through a Glass Slab and Dispersion
1 question from 1 paper, each with its answer.
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Concepts tested
- Dispersion in a parallel-sided slab
All Questions
2004 AIPMT 1 question
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A beam of light composed of red and green rays is incident obliquely at a point on the face of a rectangular glass slab. When coming out on the opposite parallel face, the red and green rays emerge from :-The refractive index of glass is different for different colours: $\mu_{green} \gt \mu_{red}$ (by Cauchy's relation, $\mu$ is larger for shorter wavelengths).
At the first face, both rays have the same angle of incidence $i$, but by Snell's law $\sin i = \mu \sin r$, the green ray is bent more (smaller $r$) than the red ray. So the two rays travel in different directions inside the slab.
Because they travel along different paths, they strike the second face at two different points.
At the second face (parallel to the first), each ray emerges at an angle equal to the original angle of incidence $i$, since a parallel slab produces only a lateral shift and no deviation.
So the red and green rays emerge from two points, propagating in two different parallel directions (both parallel to the incident beam).