JEE MAIN - Physics (2023 - 30th January Evening Shift - No. 9)
A thin prism $P_1$ with an angle $6^{\circ}$ and made of glass of refractive index $1.54$ is combined with another prism $P_2$ made from glass of refractive index $1.72$ to produce dispersion without average deviation. The angle of prism $P_2$ is
$4.5^{\circ}$
$7.8^{\circ}$
$1.3^{\circ}$
$6^{\circ}$
Explanation
$$({\mu _1} - 1){A_1} = ({\mu _2} - 1){A_2}$$
$$ \Rightarrow (1.54 - 1)6 = (1.72 - 1){A_2}$$
$${A_2} = \left( {{{0.54} \over {0.72}} \times 6} \right) = {{18} \over 4} = \left( {{9 \over 2}} \right) = 4.5^\circ $$
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