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Question
Can the dispersive power \[\omega = \frac{\mu_u - \mu_r}{\mu - 1}\] be negative? What is the sign of ω if a hollow prism is immersed into water?
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Solution
No, it cannot be negative, as the refractive index for violet light is always greater than that for red light. Also, refractive index is inversely proportional to \[\lambda^2.\] The sign of ω will be positive, as \[\mu\] is still greater than 1 and as \[\mu_v > \mu_r.\]
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