A 600 line/mm diffraction grating is in an empty aquarium tank. The index of refraction of the glass walls is n_glass = 1.50. A helium-neon laser (λ = 633 nm) is outside the aquarium. The laser beam passes through the glass wall and illuminates the diffraction grating.
a. What is the first-order diffraction angle of the laser beam?
b. What is the first-order diffraction angle of the laser beam after the aquarium is filled with water (n_water = 1.33)?