Refraction

Refraction is the passage of light from one optical medium into another across a boundary. The angle of incidence $i$ (in the first medium) and angle of refraction $r$ (in the second medium) are both measured from the normal drawn at the point of incidence. Snell's law of refraction states: (a) the incident ray, refracted ray and normal are coplanar; and (b) $\dfrac{\sin i}{\sin r}=\dfrac{n_2}{n_1}$, the ratio of the refractive index of the second medium to that of the first -- equivalently, in the often more convenient product form, $n_1\sin i = n_2\sin r$. Passing from a rarer into a denser medium bends the ray towards the normal; passing from a denser into a rarer medium bends it away from the normal. At any real refracting surface, some light is always simultaneou …