Question

A point source of light is located at the bottom of a steel tank, and an opaque circular card of radius is placed horizontally over it. A transparent fluid is gently added to the tank so that the card floats on the fluid surface with its center directly above the light source. No light is seen by an observer above the surface until the fluid is deep. What is the index of refraction of the fluid

Answer 1

Start by using the addition as a sign and use multiplying