Question

An isosceles prism of angle ${120}^o$ has a refractive index 1.44. Two parallel monochromatic rays enter the prism parallel to each other in air as shown in Fig 13.76. The rays emerging from the opposite faces :

• A. are parallel to each other
• B. are diverging
• C. make an angle of $2si{n}^{-1}\left(0.72\right)$ with each other
• D. make an angle of $2\left[si{n}^{-1}\right(0.72)-{30}^o]$ with each other

Answer 1

Answer: (D)

make an angle of $2\left[si{n}^{-1}\right(0.72)-{30}^o]$ with each other

no refraction takes place as it is incident normal
$i=r=0$

$r^{{}^{\prime }}=A-r=30-0=30$

apply Snell's law at the second surface

${\mu }_{1}sin{\alpha }_1={\mu }_{2}sin{\alpha }_2$

$1.44\times sin30=1\times sin{i}_e$

$sin{i}_e=\frac{1.44}{2}$

the deviation is $si{n}^{-1}0.72$

the angle between two rays is $2si{n}^{-1}0.72$

option $D$ is correct