A light beam in the air strikes a flat layer of pure quartz of thickness t placed in contact with a thick layer of turpentine oil. The beam is incident on the air-quartz interface at an angle of 28° with respect to the normal to the surface and emerges at angle θ_r in the turpentine. Determine θ_r. The refractive indices of quartz and turpentine are 1.54 and 1.47 respectively.