The general rule for the relationship between the angles of incidence and refraction is called Snell's law: n1sinθ1=n2sinθ2. The n refers to the material's "index of refraction." It turns out that while all wavelengths of light travel at the same speed in vacuum, they are slower when traveling through a medium. The index of refraction is defined as n = c/v, where c is the speed of light in vacuum (2.998*10^8 m/s) and v is its speed in the medium. So it's dimensionless, and since v is always less than c, then n is always greater than 1. It is only exactly 1 in vacuum. Even in air, n = 1.0003, but this is close enough to 1 that we just say it's 1. What is the c (speed of light) if n1 = 1 and n2 = 1.33?