What is the index of refraction of a medium if the critical angle is 40.0°, assuming the second medium is air?

Explanation:

The refractive index of a medium (n) is defined as angle of refraction per angle of incidence. When the angle of incidence in water reaches a certain critical value, the refracted ray lies along the boundary, having an angle of refraction of 90-degrees. This angle of incidence is known as the critical angle which was given to us; 40.0°.  Then we subtitute the value in the equation to get the R.I of the medium.