A narrow beam of light incident on a plane-parallel plate of thickness d = 20 cm with a refractive index n = 1.5 at an angle a = 60° to the normal is partially reflected from its first face and partially refracted. The refracted beam of light reaches the second face, here again it is partially refracted and leaves the plate, and partially reflected and goes to the upper face; here, refracting again, it comes out from the first face of the plate (Fig.). Find the displacement of the light beam emerging from the second face of the plate and the distance BD between the beams reflected from both faces.

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