When light passes at an angle to the normal from one material into another material in which its speed is different how does the angle with the normal change.
The refractive index n of a material is the factor by which the speed of light in the material is reduced as compared to the speed of light in vacuum. If the velocity of light in the material is Vm and Vc is the velocity of light in vacuum, Vm = Vc/n.
When light passes from one material with a refractive index n1 to another material with a refractive index n2, Snell's law applies to the angles made with the normal. n1*sin A1 = n2*sin A2 where A1 is the angle made with the normal in the first material from which it is moving out and A2 is the angle made with the normal in the material it is moving into.
If the velocity of light in the second material is higher it bends away from the normal and if the velocity in the second material is lower it bends towards the normal.