Question
Two light beams fall on a transparent material block at point 1 and 2 with angle $\theta_{1}$ and $\theta_{2}$, respectively, as shown in figure. After refraction, the beams intersect at point 3 which is exactly on the interface at other end of the block. Given : the distance between 1 and $2, d=4 \sqrt{3} \mathrm{~cm}$ and $\theta_{1}=\theta_{2}=\cos ^{-1}\left(\frac{n_{2}}{2 n_{1}}\right)$, where refractive index of the block $\mathrm{n}_{2}>$ refractive index of the outside medium $n_{1}$, then the thickness of the block is
____________ cm .
____________ cm .
