Question

What is the formula for finding the refractive index?

Answer 1

(sin i / sin r) where i = angle of incidence r = angle of refraction

Answer 2

The refractive index of a material is defined as \[n=\frac{ c }{ v }\]
where c is the speed of light in empty space and v is the speed of light in the material.
The other definition given in terms of angles of incidence and refraction is equivalent to the definition in terms of speeds.