In the diagram on the right, an incident plane wave in the direction of the ray IO strikes the interface between two media of refractive indices n 1 and n 2 at point O. Part of the wave is reflected in the direction OR, and part refracted in the direction OT. The angles that the incident, reflected and refracted rays make to the normal of the interface are given as θ i, θ r and θ t, respectively. The relationship between these angles is given by the law of reflection : θ θ i = θ θ r , and Snell's law : n 1 sin ⁡ ⁡ θ θ i = n 2 sin ⁡ ⁡ θ θ t .