An unpolarised light is incident on a plate of refractive index 3  and the reflected light is found to be completely plane polarized.  The angles of incidence and refraction are respectively

Refractive index μ=3   ip=Tan−1(μ)        (  ∵μ=Tanip  ) ip=Tan−1(3) ip=600 ∴θp=ip=600 Angle of refraction r=900−tan−1(μ)        r=90−ip          (  ∵tan−1(μ)=ip )         =900−600 ∴  r=300