how to find refractive index

To find the refractive index of an object we can use the following methods

1.  we can use this elation, n = c/n,  were c is speed of light in vacuum and  v is speed of light in the medium
2.  for prism , it is the inverse of the angle of deviation
3.  for water isthe ratio of the real dept to that of the apparent depth n = real depth/ apparent depth