Question

A cup with refractive index n2 = 1.8 has outer radius b = 6.0 cm and inner radius a = 4.0 cm. It is filled with a liquid with refractive index n3 = 1.3. In the surrounding medium with n1 = 1.0,a ray of light travels along a trajectory that is at a perpendicular distance y from the center of the cup. The ray enters the cup and, reaching the liquid interface at the critical angle, undergoes total internal reflection. Determine the distance y