This is a simulation that you can download and run on your Windows computer. Below is a screen shot of the reflectance graph. If you decide to download and install the simulation program you will be able to adjust the knobs and buttons you see below.
As a beam travels from one material through a barrier and into another, part of it is reflected and the other part passes through. The ratio of reflected beam to the original beam is called "reflectance" denoted by "R".
Waves that have a perpendicular polarization have different values for R than do waves of parallel polarization. R also depends on the two indices of refraction of the materials on either side of the barrier.
There are two important angles being caluated in this model. The first is the Brewster angle. This is the angle at which a beam can penetrate a barrier with little or no reflection. The second is the critical angle. This is the angle at which a beam is completely reflected off of the barrier.
Try to figure out what values of N1 & N2 give you a criticle angle of 55 degrees. Be aware that some times the criticle angle disappears!