A monochromatic light is incident from air on a refracting surface of a prism of angle 750 and refractive index n0 =3 . The other refracting surface of the prism is coated by a thin film of material of refractive index n as shown in figure. The light suffers total internal reflection at the coated prism surface for an incidence angle of θ≤600 . The value of n2 is