A flat piece of glass covers the top of a vertical cylinder that is completely filled with water. If a ray of light traveling in the glass is incident on the interface with the water at an angle of θa = 36.2°, the ray refracted into the water makes an angle of 49.8o with the normal to the interface. What is the smallest value of the incident angle ua for which none of the ray refracts into the water?

A flat piece of glass covers the top of a vertical cylinder that is completely filled with water. If a ray of light traveling in the glass is incident on the interface with the water at an angle of θa = 36.2°, the ray refracted into the water makes an angle of 49.8o with the normal to the interface. What is the smallest value of the incident angle ua for which none of the ray refracts into the water?