Final answer:
The refractive index of the plastic can be found using Brewster's angle of 50 degrees and Snell's Law, resulting in the index being the tangent of 50 degrees. To find the Brewster’s angle for light in water reflected from crown glass, the refractive index of the crown glass is required.
Step-by-step explanation:
The question relates to the concept of Brewster's angle in physics. Brewster's angle is the angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent surface, with no reflection. According to Snell's Law and the Brewster's angle equation, the refractive index n of a material can be calculated using the formula n = tan(\theta_{B}), where \(\theta_B\) is Brewster's angle.
Given that Brewster's angle for light traveling in water and falling on a plastic block is 50 degrees, we can calculate the refractive index of the plastic using the formula:
n = tan(50 degrees)
For the part of the question regarding Brewster's angle for light traveling in water and reflected from crown glass, we would need the refractive index of crown glass to find Brewster's angle using the same Brewster's principle. Typically, the refractive index for crown glass is known from reference materials, and Brewster's angle can be calculated if this index is provided.