Ray Optics

JEE Main level, numerical answer, medium

260 of 295

Question 260 of 295

A deviation of 2∘2^{\circ} is produced in the yellow ray when prism of crown and flint glass are achromatically combined. Taking dispersive powers of crown and flint glass are 0.020.02 and 0.030.03 respectively and refractive index for yellow light for these glasses are 1.51.5 and 1.61.6 respectively. The refracting angles for crown glass prism will be ________∘^{\circ} (in degree)
(Round off to the Nearest Integer)

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Answer: 12

ω1=0.02;μ1=1.5;ω2=0.03;μ2=1.6{\omega }_{1}=0.02;{\mu }_{1}=1.5;{\omega }_{2}=0.03;{\mu }_{2}=1.6
Achromatic combination

∴θnet=0∴{\theta }_{net}=0
θ1−θ2=0{\theta }_{1}-{\theta }_{2}=0
θ1=θ2{\theta }_{1}={\theta }_{2}
ω1δ1=ω2δ2{\omega }_{1}{\delta }_{1}={\omega }_{2}{\delta }_{2}
and
δnet=δ1−δ2=2∘{\delta }_{net}={\delta }_{1}-{\delta }_{2}=2^{\circ}
δ1−ω1δ1ω2=2∘{\delta }_{1}-\dfrac{{\omega }_{1}{\delta }_{1}}{{\omega }_{2}}=2^{\circ}
δ1(1−ω1ω2)=2∘{\delta }_{1}\left(1-\dfrac{{\omega }_{1}}{{\omega }_{2}}\right)=2^{\circ}
δ1(1−23)=2∘{\delta }_{1}\left(1-\dfrac{2}{3}\right)=2^{\circ}
δ1=6∘{\delta }_{1}=6^{\circ}
δ1=(μ1−1)A1{\delta }_{1}=\left({\mu }_{1}-1\right){A}_{1}
6∘=(1.5−1)A16^{\circ}=\left(1.5-1\right){A}_{1}
A1=12∘{A}_{1}=12^{\circ}

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