A glass U-tube with refractive index n = 1.52 is constructed by bending a glass rod into a U-shape, where the curved parts of the tube are two arcs of a semicircle. A collimated beam of light falls perpendicularly on the flat surface A. Determine the minimum value of the ratio " for which all light entering the glass through surface A will emerge from the glass through surface B. Leave your answer to 3 significant figures. R d A B