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Question
By properly combining two prisms made of different materials, it is possible to
(a) have dispersion without average deviation
(b) have deviation without dispersion
(c) have both dispersion and average deviation
(d) have neither dispersion nor average deviation
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Solution
(a) have dispersion without average deviation
(b) have deviation without dispersion
(c) have both dispersion and average deviation
Consider the case of prisms combined such that the refractive angles are reversed w.r.t. each other. Then, the net deviation of the yellow ray will be \[\delta_y = ( \mu_y - 1)A - ( \mu_y ' - 1)A'\]
And, the net angular dispersion will be \[\delta_y - \delta_r = \left( \mu_y - 1 \right)A\left( \omega - \omega' \right)\]
Thus, by choosing appropriate conditions, we can have the above mentioned cases.
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