Ray Optics

JEE Main level, single correct, medium

239 of 295

Question 239 of 295

A thin prism with angle 5∘5^{\circ} of refractive index 1.72 is combined with another prism of refractive index 1.9 to produce dispersion without deviation. The angle of second prism is ____\_\_\_\_.

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Answer: (C) 4∘4^{\circ}

For dispersion without deviation, the condition is (μ1−1)A1+(μ2−1)A2=0(\mu_1 - 1)A_1 + (\mu_2 - 1)A_2 = 0.
Substituting values: (1.72−1)×5+(1.9−1)×A2=0(1.72 - 1) \times 5 + (1.9 - 1) \times A_2 = 0
0.72×5+0.9×A2=00.72 \times 5 + 0.9 \times A_2 = 0
3.6+0.9A2=03.6 + 0.9 A_2 = 0
A2=−4°A_2 = -4°
The magnitude of the second prism angle is 4°.

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