Part 1 of question: Consider the case when light passes from one medium into another medium that has a lower index of refraction, for instance, from glass to water. Is there an angle of incidence for which the refracted angle is 90 degrees? If there is, derive an expression for this angel in terms of the two indicies of refraction.
Part 2 of question: will there be any refraction of light waves if the metal slit is placed on the rear glass plate directly behind the ethced line on the front plate?