Suppose you illuminate two thin slits by monochromatic coherent light in air and find that they produce their first interference minima at ±35.20° on either side of the central bright spot. You then immerse these slits in a transparent liquid and illuminate them with the same light. Now you find that the first minima occur at ±19.46° instead. What is the index of refraction of this liquid?

Suppose you illuminate two thin slits by monochromatic coherent light in air and find that they produce their first interference minima at ±35.20° on either side of the central bright spot. You then immerse these slits in a transparent liquid and illuminate them with the same light. Now you find that the first minima occur at ±19.46° instead. What is the index of refraction of this liquid?