<P> In optical instruments, dispersion leads to chromatic aberration; a color - dependent blurring that sometimes is the resolution - limiting effect . This was especially true in refracting telescopes, before the invention of achromatic objective lenses . </P> <P> In a conducting medium, permittivity and index of refraction are complex - valued . Consequently, so are the angle of refraction and the wave - vector . This implies that, while the surfaces of constant real phase are planes whose normals make an angle equal to the angle of refraction with the interface normal, the surfaces of constant amplitude, in contrast, are planes parallel to the interface itself . Since these two planes do not in general coincide with each other, the wave is said to be inhomogeneous . The refracted wave is exponentially attenuated, with exponent proportional to the imaginary component of the index of refraction . </P>

Relationship between critical angle of water and the glass is