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  4. In a direct vision spectroscope, one uses a flint and a crown glass prism combination to get zero mean deviation but a finite dispersion. Which of the following is an acceptable diagrammatic representation? [C= crown , F= flint, V= violet, R= red ]

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Q. In a direct vision spectroscope, one uses a flint and a crown glass prism combination to get zero mean deviation but a finite dispersion. Which of the following is an acceptable diagrammatic representation? $[C=$ crown $, F=$ flint, $V=$ violet, $R=$ red $]$

Ray Optics and Optical Instruments

Solution:

In a prism combination for dispersion, without deviation, the yellow ray comes out undeviated. As $\mu_{V} > \mu_{R}$, violet deviates more than red. Since $\mu_{F} > \mu_{C}$ ' $A_{F} < A_{C}$ as the condition for no deviation is $(\mu_{F}-1) A_{F}$ $=(\mu_{C}-1) \cdot A_{C}$