A ray of light travelling in glass $\left( {{\rm{\mu }} = \frac{3}{2}} \right)$ is incident on a horizontal glass air surface at the critical angle ${{\rm{\theta }}_c}$. If thin layer of water $\left( {{\rm{\mu }} = \frac{4}{3}} \right)$ is now poured on the glass air surface, the angle at which the ray emerges into air the water-air surface is<br /> 