What happens when a ray of light strikes the surface of separation between the two media at right angle?

When light enters the boundary of two surfaces at right it passes normally without deviation.
This is because here angle of incidence at the boundary of two mediums is zero.
By Snell’s law 
$\begin{array}{l}\frac{\sin i}{\sin r}=\mu \\ \because i=0=>\sin i=0\\ \sin r=\frac{\sin i}{\mu }\\ =>\sin r=0\\ =>r=0\\ \text{We see angle of refraction also becomes 0}\text{.}\\ \text{Thus light ray doesn't deviate from the normal at the boundary. }\end{array}$