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Two small angled prisms A and B deviate ...

Two small angled prisms A and B deviate the blue rays by `6^(@)and8^(@)` and the red rays by `4^(@)and6^(@)` respectively. Which prism has a greater dispersive power?

Text Solution

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(a) Angular dispersion = `A = 6^(@) - 4^(@) = 2^(@)`
Mean deviation of `A = (6+4)/(2) = 5^(@)`
Dispersive power of `A = (2)/(5) = 0.4`
(b) Angular dispersion of `B = 8^(@) - 6^(@) = 2^(@)`
Mean deviation of `B = (8+6)/(2) = 7^(@)`
Dispersive power of `B = (2)/(7) = 0.2857`
Hence, dispersive power of A is greater than that of B.
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