A glass prism ' A ' deviates the red and blue rays through 10° and 12° respectively. A second prism ' B ' deviates them through 8° and 10° respectively. The ratio of their dispersive powers is (A to B) (a) 9: 13 (b) 4: 5 (c) 9: 11 (d) 8: 9

Answer: (c). Dispersive power ω = δb - δrδmean, with δmean = (δb + δr)/(2) Prism A: ωA = (12 - 10)/(11) = 2/11; prism B: ωB = (10 - 8)/(9) = 2/9 ωA: ωB = 2/11: 2/9 = 9: 11, so the answer is (c).

A glass prism ' A ' deviates the red and blue rays through 10° and… | MHT CET 2024 (15 May, Shift 2)

Q37MHT CET 2024 · 15 MAY · SHIFT 2Medium

Prism, Dispersion & Scattering

A glass prism ' A ' deviates the red and blue rays through $10^\circ$ and $12^\circ$ respectively. A second prism ' B ' deviates them through $8^\circ$ and $10^\circ$ respectively. The ratio of their dispersive powers is (A to B)

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Answer: (c)

Dispersive power $\omega = \dfrac{\delta_b - \delta_r}{\delta_{\text{mean}}}$ , with $\delta_{\text{mean}} = \frac{\delta_b + \delta_r}{2}$
Prism A: $\omega_A = \frac{12 - 10}{11} = \frac{2}{11}$ ; prism B: $\omega_B = \frac{10 - 8}{9} = \frac{2}{9}$
$\omega_A : \omega_B = \frac{2}{11} : \frac{2}{9} = 9 : 11$ , so the answer is (c).

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Prism, Dispersion & Scattering question from MHT CET 2024 (15 May, Shift 2)

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