1. Speed of Light :- Light is composed of photons and photons travels only c = 3 x 108 m/s At the speed And travels fastest in vacuum C=3 10 8 In air =c/1.0003 In water =c/1.33 In glass=c/1.5

2. Index of Refraction 1- Absolute Index of Refraction of material :-is defined n=speed of light in vacuum/speed of light in the material =c/v 2- Small's Law index of refraction of material :- ni sinθ=nt sinθ Refraction :- When a ray of light is transmitted obliquely through the boundary between two material of unlike index of refraction the ray bends.

3. Component of refraction

4. Property of the refraction :- 1- If n1 ˃ n2 the ray refract bends toward the normal as it enters the second material 2- If n1 ˂ n2 the ray refract bends away from the normal components refraction.- 1-Angle of incidencei 2-Angle of refracted t(transmission ) The incident and refracted rays and the normal all lie in the same plane

6. Snell’s law:- ni sin i =nt sint Critical Angle :- Critical Angle c The condition of Critical Angle ;- 1- ray passes from a material of higher index of refraction to one of lower index 2- i<t and t =90 then i = c