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, $$d = 4\sqrt{3} cm$$ and $$\theta_{1} = \theta_{2} = \cos^{-1}(\frac{n_{2}}{2n_{1}})$$, where refractive index of the block $$n_{2} > $$ refractive index of the outside medium $$n_{1}$$, then the thickness of the block is ________cm.