A prism with an optimal refractive angle of 6.0 degrees (Considered a small angle) is placed in the air. Project an arrow, parallel white light beam at the side of the prism in a direction perpendicular to the bisectoral plane of the refractive index, very close to the edge of the prism. Place a screen E behind the prism, perpendicular to the direction of the incident beam and 1.2m from the bisector plane of the refractive angle. The refractive index of the prism for red light is and for purple light is. The width from red to purple of the continus spectrum on the screen is